NEW PROCESS FOR THE MANUFACTURE OF BEER.
§ I. Preliminary experiments 338
§ II. Method of estimating the oxygen held in solution in wort 353
§ III. On the quantity of oxygen existing in a state of solution in
brewers’ worts 364
§ IV. On the combination of oxygen with wort 371
§ V. On the influence of oxygen in combination on the clarification of
wort 381
§ VI. Application of the principles of the new process of brewing with
the use of limited quantities of air 387
APPENDIX 396
INDEX 403
INDEX TO PLATES.
I. Principal disease-ferments met with in wort and beer 6
II. Appearance under the microscope of the deposit from “turned” beer 20
III. _Torulæ_ in process of development 72
IV. _Mycoderma vini_ functioning as an alcoholic ferment.—Right half,
showing appearance of spores just sown; left half, their appearance
after an interval of submerged life 116
V. _Mucor_, vegetating submerged, in deficit of air 136
VI. Ferment of _mucor_ 138
VII. Yeast-cells—worn out and dissociated (left), after revival in a
sweet wort (right) 148
VIII. Fertile mould-cells from the outer surface of grapes 152
IX. Various examples of the mode of growth of mould-cells from the outer
surface of grapes 154
X. One of the ferments of acid fruits at the commencement of
fermentation in its natural _medium_ 166
XI. _Saccharomyces pastorianus_, in course of regular growth 168
XII. Ferment-cells from a spontaneous fermentation just starting 184
CHAPTER I.
On the Intimate Relation existing between the Deterioration of Beer, or
the Wort from which it is Made, and the Process of Brewing.
At the outset of these “Studies,” let us briefly consider the nature of
beer and the methods of its manufacture.
Beer is a beverage which has been known from the earliest times. It may
be described as an infusion of germinated barley and hops, which has
been caused to ferment after having been cooled, and which, by means of
“settling” and racking, has ultimately been brought to a high state of
clarification. It is an alcoholic beverage, vegetable in its origin—a
_barley wine_, as it is sometimes rightly termed.[1]
Beer and wine, however, differ widely in their composition. Beer is less
acid and less alcoholic than wine; it holds more ingredients in
solution, and the nature of these ingredients is by no means similar to
that of those which are found in wine.
These differences in the component parts of wine and beer give rise to
corresponding differences in the keeping qualities of the two liquids.
The small amount of acidity in beer, its poverty in alcohol, and the
presence of matter that is saccharine, or liable to become so, all
operate in imparting to beer a tendency to change, which wine does not
possess. That this unequal resistance to the aggression of diseases is
due to such differences, may be proved by the fact that wine could be
made much more liable to change than it actually is, by a diminution of
its acidity and its usual proportion of alcohol, or by increasing the
proportion of viscid or saccharine matters,[2] modifications which would
tend to assimilate its composition to that of beer.
We have remarked elsewhere that the pains devoted to the rearing of
vines, and to the ordinary operations of vinification, such as
_ouillage_,[3] sulphuring, and repeated rackings, as well as the use of
cellars and vessels hermetically closed, are entailed by the necessity
of counteracting and preventing the diseases to which wine is liable.
The same may be said, _a fortiori_, of beer, inasmuch as it is more
liable to change than wine. Manufacturers and retailers of this beverage
have to strive constantly with the difficulty of preserving it, or the
wort used in its manufacture. We may readily be convinced of this by
reviewing the usual processes of the art of brewing.
When the infusion of malt and hops, which is termed wort, is completed,
it is left to cool. It is next put into one or more casks or vats, in
which it is made to undergo alcoholic fermentation—the most important of
all the processes in brewing.
The cooling must be as rapid as possible. This is a condition of
success; otherwise, the wort may deteriorate, which will necessarily
lead to deterioration in the quality of the beer. As long as the wort is
at a high temperature it will remain sound; when under 70° C. (158° F.),
and particularly when at a temperature of from 25° C. to 35° C. (77° F.
to 95° F), it will be quickly invaded by lactic and butyric ferments.
Rapidity in cooling is so essential that to secure it recourse is had to
special apparatus.[4] Even in the preparation of wort, especially when
it is effected by successive mashings, in summer, deterioration is
imminent: in fact, it is not rare to see the wort becoming acid during
the _mashes_, if these are not accomplished with all possible celerity.
After the wort has been cooled, it is mixed with yeast. This is obtained
from a previous fermentation, and, after being thoroughly pressed, is
added at the rate of from one to two thousandth parts of the weight of
the wort, that is, from 100 to 200 grammes per hectolitre (about 4 oz.
to 8 oz. average for every 25 gallons). At first sight, this yeast seems
free from the possible diseases of the wort and beer; but this is by no
means the case.
Now, why do we add yeast to our wort? This practice is unknown in the
art of vinification. The must is always left to spontaneous
fermentation. Why should we not leave the wort to operate in the same
manner?
It would be a mistake to suppose that in the brewing of beer yeast is
added with the sole object of accelerating fermentation, and making it
more rapid. Rapidity in fermentation is a very questionable advantage,
and one which is not desired by brewers, who rather agree in
pronouncing it injurious to the quality of beer. It is in the easy
deterioration of the wort, or what is tantamount to it, in the
facility it affords to various spontaneous fermentations, that we find
an answer to these questions. The must, through its acidity, due to
the presence of bitartrate of potash—which seems to promote alcoholic
fermentation—through its proportion of sugar, and perhaps in
consequence of some other peculiarity of its composition, always
undergoes regular alcoholic fermentation. The diseases of wine, at the
commencement of its manufacture, show themselves, so to say, in a
latent state only. Therefore a vintage can be left, without
inconvenience, to spontaneous fermentation.
With wort the case is quite different. Under certain accidental
circumstances it is possible that alcoholic fermentation alone may take
place in a wort left to ferment spontaneously, and the quality of the
beer remain unimpaired, but such an event would be exceptional, and of
very rare occurrence. In most cases we should obtain an acid or putrid
liquid resulting from the production and multiplication of alien
ferments.
The addition of yeast is made in consequence of the necessity of
exciting through the whole bulk of wort, as soon as it is cold, a single
fermentation—viz., the alcoholic, the only one that can produce beer
properly so called.
The alcoholic ferments concerned in the production of beer will be found
represented in several of the engravings in this work. Other ferments we
may term “diseased”; these include all those that may occur
spontaneously—that is, whose germs have not been directly and
intentionally introduced—amongst the actual alcoholic ferments.
The expression, “diseased ferments,” is justified by the circumstance
that the propagation of these ferments is always accompanied by the
production of substances which are acid, putrid, viscous, bitter, or
otherwise unpalatable, a consideration of commercial rather than
scientific importance. From a physiological point of view, all these
ferments are of equal interest and importance. The botanist, as a man of
science, in contemplating nature, must give equal attention to all
plants, whether useful or noxious, since they are all governed by the
same natural laws, among which no order of merit could be established.
The exigencies of industry and health require, however, wide
distinctions.
[Illustration: Plate 1. Principal Disease-ferments met with in Wort and
Beer.]
The first engraving (Plate I.) represents the different diseased
ferments, together with some cells of alcoholic yeast, to show the
relative size of these organisms.
No. 1 of the engraving represents the ferments of _turned_ beer, as it
is called. These are filaments, simple or articulated into chains of
different size, and having a diameter of about the thousandth part of a
millimetre (about 1/25000 inch). Under a very high power they are seen
to be composed of many series of shorter filaments, immovable in their
articulations, which are scarcely visible.
In No. 2 are given the lactic ferments of wort and beer. These are
small, fine and contracted in their middle. They are generally detached,
but sometimes occur in chains of two or three. Their diameter is a
little greater than that of No. 1.
In No. 3 are given the ferments of putrid wort and beer. These are
mobile filaments whose movements are more or less rapid, according to
the temperature. Their diameter varies, but is for the most part greater
than that of the filaments of Nos. 1 and 2. They generally appear at the
commencement of fermentation, when it is slow, and are almost invariably
the result of very defective working.
In No. 4 are given the ferments of viscous wort, and those of ropy beer,
which the French call _filante_. They form chaplets of nearly spherical
grains. These ferments rarely occur in wort, and still less frequently
in beer.
No. 5 represents the ferments of pungent, sour beer, which possesses an
acetic odour. These ferments occur in the shape of chaplets, and consist
of the _mycoderma aceti_, which bears a close resemblance to lactic
ferments (No. 2), especially in the early stages of development. Their
physiological functions are widely different, in spite of this
similarity.
The ferments given in No. 7 characterize beer of a peculiar acidity,
which reminds one more or less of unripe, acid fruit, with an odour _sui
generis_. These ferments occur in the form of grains which resemble
little spherical points, placed two together, or forming squares. They
are generally found with the filaments of No. 1, and are more to be
feared than the latter, which cause no very great deterioration in the
quality of beer, when alone. When No. 7 is present, by itself or with
No. 1, the beer acquires a sour taste and smell that render it
detestable. We have met with this ferment existing in beer,
unaccompanied by other ferments, and have been convinced of its fatal
effects.
No. 6 represents one of the deposits belonging to wort. This must not be
confounded with the deposits of diseased ferments. The latter are always
visibly organized, whilst the former is shapeless, although it would not
always be easy to decide between the two characters, if several samples
of both descriptions were not present. This shapeless deposit interferes
with wort during its cooling. It is generally absent from beer, because
it remains in the backs, or on the coolers; or it may get entangled in
the yeast during fermentation and disappear with it.
Among the shapeless granulations of No. 6 may be discerned little
spheres of different sizes and perfect regularity. These are balls of
resinous and colouring matter that are frequently found in old beer, at
the bottom of bottles or casks; sometimes they occur in wort preserved
after Appert’s method. They resemble organized products, but are nothing
of the kind. We have remarked before, in “Studies on Wine,” that the
colouring matter of wine would settle, in course of time, in that form.
It is evident that the different ferments delineated in Plate I. are
worthy of thorough study, in consequence of the fermentations to which
they may give rise. Care must be taken to isolate the action of each of
them in fermentations which we may call pure—a condition of some
difficulty, but one that may be carried out by an adoption of the
methods explained in this work.
All these diseased ferments have a common origin. Their germs,
infinitesimal and hardly perceptible as they are, even with the aid of
the microscope, form a part of the dust conveyed through the air. This
dust the air is continually taking from or depositing upon all objects
in nature, so that the dust that clings to the ingredients from which
our beer is manufactured, may teem with the germs of diseased ferments.
During the process of fermentation, the occult power of diseased
ferments, although it may escape the observation of the brewer, is
manifested in a high degree.
During the last thirty years, or so, the art of brewing has undergone a
radical change, at least in Europe. This change has been effected by a
partial abandonment of the process of fermentation formerly used. Thirty
years ago only one kind of beer was known; there are nowadays two
distinct kinds—beer fermented at a high temperature, and beer fermented
at a low temperature. Each of these is subdivided into many varieties,
to which different names are given, according to their strength or
colour. This is the case in England, where we find porter, ale, pale
ale, stout, bitter beer, and other varieties of beer, although, as a
matter of fact, the English have but one kind of beer, all the English
beers being fermented at a high temperature.
Let us briefly examine the differences existing between the two kinds of
beer.
Formerly all beer was fermented at a high temperature. The wort, after
having been cooled in the backs, was run into a large vat, at a
temperature of about 20° C. (68° F.). Yeast was then added to it, and
when the fermentation began to show itself, in the formation of a light,
white froth, upon the surface of the liquid, the wort was run into
casks, having a capacity of from 50 to 100 litres (11 to 22 gallons)—75
litres being the commonest size. These casks were placed in cellars,
having a temperature of from 18° C. to 20° C. (64° F. to 68° F.). The
activity of fermentation soon produced a froth that grew thicker and
more and more viscous in proportion to the quantity of yeast it
contained. The yeast worked out of the bung-holes and dropped into a
vessel placed under the casks; there it was gathered for subsequent
operations. It always exceeded the quantity used in the first instance,
the ferment increasing greatly during the process of fermentation. The
increase in its weight varied with the weight of yeast used and the
composition of the wort. Under the ordinary conditions of brewing, where
the weight of the pitching yeast was about one thousandth part of the
weight of the wort, the increase is said to have been from five to seven
times the weight of the yeast; but such increase must naturally have
been determined by the quality of the wort, the quantity of hops used,
the action of oxygen, and the proportion of barm employed. The process
of fermentation lasted from three to four days. By that time the beer
was finished, and had become limpid, the fermentation having been
completed. The bungs could then be placed in the casks, and the beer be
delivered to the customer.[5] A certain amount of yeast still remained
in the casks, and caused the beer to become thick, in transit; but a few
days’ rest sufficed to restore its brilliancy, and render it fit for
drinking or bottling.
Here we have an explanation of the term “_high_ fermentation,” which has
been applied to the foregoing process. This process is conducted at a
high temperature, which, commencing at 19° C. or 20° C. (66° F. or 68°
F.), is raised to 20° C. or 21° C. (68° or 70° F.) by the action of
fermentation, which is always accompanied by an increase of heat.[6]
This is not, however, the only reason for the use of the term “_high_
fermentation.” We have just seen that the fermenting casks were so
arranged that most of the yeast produced during the process of
fermentation would rise to the upper part of the casks and work out of
the bung-holes. In this practical fact we have the actual origin of the
expressions “_high fermentation_” and “_high beer_,” which are used to
distinguish this peculiar fermentation and the quality of beer derived
from it.
As we have already observed, all beer was formerly produced by this mode
of fermentation, which even at the present time is still practised in
the breweries of Great Britain, where beer fermented at a low
temperature is absolutely unknown.
“Low fermentation” is a slow process, effected at a low temperature,
during which the yeast sinks to the bottom of the vats or casks. The
wort, after cooling, is run into open wooden vats. In cooling, the wort
is brought to as low a temperature as 8° C. (47° F.), or even 6° C. (43°
F.), at which point it is maintained by cones or cylinders (styled
_nageurs_, i.e., floats, by the French) floating in the fermenting vats.
These floats may be filled with ice if the outside temperature requires
it, as is invariably the case in summer.
The duration of this fermentation is ten, fifteen, or even twenty days.
The yeast, which is produced less abundantly than in the case of beer
fermented at a high temperature, is gathered after the beer has been
drawn off, and is partly used in subsequent fermentations.
The term “_low_ fermentation” is derived partly from the lowness of the
temperature during the fermenting process, and partly from the fact that
the yeast is gathered at the bottom, and not at the upper part of the
fermenting vessels.[7]
Beer fermented at a low temperature, of which there are several
varieties, differing in colour and quality, is of Bavarian origin.[8]
The preference of the public for this kind of beer, and the increased
facilities that such a beer affords the trade, are the two reasons why
its manufacture has so greatly increased. In Austria, Bavaria, Prussia,
and other Continental countries this new method of brewing is almost
exclusively adopted.
In the _Moniteur de la Brasserie_ of the 23rd April, 1871, may be found
the following significant remarks on the increase in the production of
beer fermented at a low temperature on the Continent: “The number of
breweries manufacturing _high_ beer is rapidly decreasing, whilst the
number of those producing _low_ beer is still more rapidly increasing.
There were in Bohemia, in 1860, 281 breweries in which high fermentation
was practised; in 1865, only 81 of these remained; in 1870, the number
had declined to 18. On the other hand, the number of breweries
practising _low_ fermentation increased from 135 in 1860 to 459 in 1865,
and in 1870 had risen to 831. In 1860 there were 620 breweries in which
the two methods were employed; in 1865 there were 486; in 1870 only 119
remained. The number of breweries at present existing in Bohemia amounts
to 968.”
In France, we are still in a period of transition; but year by year the
manufacture of “low beer” is increasing, to the evident detriment of its
competitor.
It is unnecessary to dwell upon certain differences existing between the
two kinds of beer, such as may be traced to the preparation and
composition of their respective worts. The brewing of “high beer,” by
hand or machinery, is effected in one operation; the brewing of “low
beer” is accomplished by successive mashings, the temperatures of which
are gradually raised. These differences, and others that result from the
longer boiling of the wort, in the “high fermentation” process, give
rise to diversities in the composition and colour of the worts, from
which circumstance “low beers” are sometimes termed _white beers_, in
contradistinction to the others, which have a deeper colour, and are
known as _dark beers_ (_bruns_). The name of Strasburg is generally
given to “low beer” in France, but sometimes it is called German beer.
It is easy to account for the changes introduced into the construction
and working of breweries by the new process of “low fermentation.” A low
temperature is essential not only to the manufacture but also to the
preservation of “low beer,” and must be secured by the use of
ice-cellars in which the temperature may be maintained at 5° R. or 6° R.
(43° F. or 45° F.), and even at 1°, 2°, or 3° R. (35° to 39° F.)
throughout the year. This necessitates an accumulation of ice and the
construction of cellars of enormous extent, for the storage of the beer.
“Low beer” is essentially a stock beer, especially if brewed in winter,
when due advantage is taken of the low temperature of the season. It is
kept in cold cellars until the spring or summer, when beer is consumed
in larger quantities. It is calculated that 100 kilos. (1·96 cwt.) of
ice is the average quantity used per hectolitre (22 gallons) of good
beer, between the cooling of the wort and the day of sale.[9]
In the manufacture of “high beer” we find none of these complications,
nor have we in that manufacture any similar difficulty of working or
expense of construction to contend against. The whole process of
brewing, including the delivery of the beer, does not take more than
eight days. Why should a mode of brewing so simple, so rapid, and
comparatively so inexpensive, have been abandoned by the greater part of
Europe in favour of a system disadvantageous to the brewer in so many
respects? It would be a mistake to suppose that the sole reason for such
a change might be found in the superior quality of “low beer.” That such
a superiority does exist is admitted as a fact by the majority of beer
drinkers; but taken by itself, this fact is not sufficient to account
for the radical transformation that has taken place in the manufacture
of beer, as is proved by the example of England, which, we believe, does
not possess as yet one single “low beer” brewery, from which
circumstance we may fairly suppose that the English have a decided
preference for “high beer.”
The principal advantage of working at a low temperature lies in the fact
that “low beer” is less liable to deterioration, and is less prone to
contract diseases than “high beer,” especially whilst it remains in the
brewery—a circumstance that places the brewer in a position vastly
superior to that which he occupied in former times. With the help of ice
the brewer can manufacture beer during winter and the early part of
spring, for consumption in summer.[10] “High beer,” on the other hand,
must be consumed within a short time of its production. The brewer is
thus compelled to manufacture it as it is wanted, and as orders are sent
in, the demand for it being in a great measure dependent upon the state
of the weather.
Conditions so unfavourable as these must necessarily operate
prejudicially against trade. Industry requires more stability and
uniformity, both in the production and the sale of its goods. “Low beer”
can be brewed in large quantities at any time to be delivered at any
other time, according to requirements; its manufacture, therefore, is
unattended by the inconveniences which we have just noticed.[11]
How is it that the use of ice and yeast operating at a low temperature
so greatly facilitates the preservation of our beer and enables us to
secure such striking advantages? The explanation is simple: the diseased
ferments, which we have pointed out, rarely appear at a lower
temperature than 10° C. (50° F.), and at that temperature their germs
cease to be active. The adoption of low temperatures by brewers is
mainly due to this physiological fact. On one occasion only have we met
with active _vibrios_ (No. 3, Plate I.), at a very low temperature;
these were forming with great difficulty in wort fermenting at 5° C.
(41° F.).
From this we see that the changes which the manufacture of beer has
undergone during the present century have been based mainly on the
diseases to which beer is liable, either during or after the process of
brewing. The fact that English brewers have not as yet adopted “low
fermentation” may be accounted for, in a great measure, by the
difficulty of enlarging existing breweries, in cities like London, to
the extent required for the new method of manufacture. Even in the event
of public taste demanding a “low beer,” English brewers will hesitate a
long time before converting their breweries. Such conversion would
impose upon them expenses and difficulties of a very serious nature. If
ever such a change should take place, it will probably be inaugurated
out of London. It is, however, worthy of remark that English brewers,
without adopting “low fermentation,” have introduced considerable
improvements in brewing, especially in the management of the temperature
during fermentation; this must be preserved within narrow and exact
limits, for fear of injury to the product. It might easily be shown that
these improvements have resulted from the liability of the beer to
contract diseases, although this fact may not have been recognized by
the brewers who have introduced them.
Besides the yeasts which belong to the two principal kinds of
fermentation, there exist many varieties of alcoholic ferment that
produce, each of them, a special kind of beer. Among these special beers
some are deficient in taste, others in aroma, others in brilliancy. Let
us suppose that in the manufacture of a beer with one of these yeasts,
from which a peculiar flavour is derived, a different and inferior
variety is accidentally mixed with that which we intend to use; in such
a case, the inferior variety, the product of which will possess an
inferior quality, will exercise such an influence on the brewing as to
induce the belief that disease must be present. The microscope, if
consulted, will reveal no special organism, nor any of those diseased
ferments of which we have given specimens. It is in the study of yeast
that we must endeavour to find the cause of the results we observe. This
point, which is of the greatest importance to brewers, will become
clearer as we proceed.
If we examine the practices of the beer trade, in its retail as well as
in its export branches, we shall find that many of them afford evidence
of the liability of the beer to deteriorate. We may cite some of these.
When taken out of the ice-cellars, the beer is kept in casks of small
capacity, that it may be the sooner consumed; when exposed to a high
temperature, the beer will not keep sound for any length of time, but
will speedily effloresce with _mycoderma vini_ or _mycoderma aceti_.
Beer which is intended for bottling should not be kept for more than a
month or six weeks. Even in bottling we may perceive the tendency of the
liquid to deteriorate.[12] It is necessary that the bottles, immediately
after being filled, should be laid on their sides for twenty-four or
forty-eight hours; they may then be placed upright; the reason for this
is that the air left between the cork and the beer might give rise to
the production of efflorescence. If we lay the bottles down on their
sides, the oxygen of this air will be absorbed by the oxidizable
substances in the liquid, and there will be little fear of germs
developing themselves when the bottles are placed upright. The bottles
should not, however, be left on their sides longer than forty-eight
hours; otherwise the supplementary fermentation may force the corks out.
Moreover, when the bottles stand upright the products of fermentation
collect at the bottom, and not at the sides.
Beer which is intended for keeping, if exported or conveyed some
distance off, must be surrounded with ice. Without this precaution it
will ferment too much or contract some disease.
“High beer” cannot stand travelling. This kind of beer should not be
exported unless the ordinary proportion of hops has been greatly
increased—hop oil acting in some respects as an antiseptic, and
preventing the beer from contracting diseases.[13] The export of English
beer to India and the Continent has fallen off of late years, or rather,
has not increased to the extent that was anticipated; in fact, this
trade has entailed great losses upon those engaged in it. It is said
that an English firm lost as much as £48,000 on one consignment, which
on its arrival in India was found to be all turned.
There are no breweries in hot countries, where beer would command a very
large sale. It is a well-known fact that beer is a remarkably pleasant
drink in tropical climates, provided its temperature be a few degrees
below that of the atmosphere, but the expenses of its production would
be enormous, on account of the immense quantity of ice that would be
required in its manufacture and for its preservation. It is in hot
countries that beer is most liable to deterioration.
Beer is said to be the beverage of northern regions, which are deprived
of the vine, by the rigour of their climate. In these regions man has
sought in the abundance of grain-fruit a substitute for grapes. To a
certain extent this is true; nevertheless, it is an undoubted fact that
beer was first brewed in Egypt, a very hot country, whence its
manufacture has spread over Europe. It was called Pelusian wine, from
Pelusium, a city on the banks of the Nile, which produced a beer that
was held in high esteem.[14]
Beyond a doubt, hot countries, even those in which the vine is
cultivated, would consume much beer, could it but stand their high
temperature.[15] A considerable quantity of beer is now brewed in
British India, but its manufacture entails an enormous outlay for ice.
The complications which result from the tendency of wort and beer to
deteriorate, underlie almost all the details of the process of brewing
and the sale of beer, and have been the cause of most of the changes and
improvements that have been effected in brewing, during the present
century.
Footnote 1:
This expression is found for the first time, it would appear, in
Theophrastus, B.C. 371. [See, however, Herodotus, Bk. II., chap. 77.
Speaking of some Egyptians he says, “They drink a kind of wine made
from barley (ὄινῳ δ’ ἐκ κριθέων πεποιημένῳ), for the grape does not
grow in that part of the country.” Herodotus wrote about 450 B.C.
Æschylus (480 B.C.) has a similar expression, Suppl. 953.—D. C. R.]
Footnote 2:
One of these modifications is a real source of serious danger to the
preservation of wine; for instance, during rainy years, at the time of
vintage, the grapes may happen to be covered with earthy matter,
consisting principally of carbonate of lime; this will dissolve in
wine and partly neutralize its acidity, and the wine will thus become
more liable to disease.
Footnote 3:
Transferring from one cask to another for the purpose of clarifying
the wine.
Footnote 4:
We shall hereafter revert to this rapidity in cooling, to show that
it is also of use in the subsequent clarification of beer.
Footnote 5:
In some breweries (at Lyons especially) fermentation at a high
temperature is practised in large vats at about 15° C. (59° F.). The
yeast which covers the surface of the liquid is skimmed off and stored
in flat tubs.
Footnote 6:
The initial temperature of the wort must be regulated by the quantity
of wort subjected to fermentation. In English breweries, where large
quantities are brewed at a time, the heat created by the action of
fermentation would produce a temperature sufficiently high to affect
the quality of the beer, if the yeast were added at 19° C. or 20° C.
The following are the temperatures at which the worts are pitched, in
the principal London breweries:—For common ale, 60° F. or 15·5° C.;
for pale ale, 58° F. or 14·4° C.; for porter, 64° F. or 17·8° C. The
fermentation is commenced in large vats; from these the beer is run
into vessels of a much smaller capacity, in which it completes its
fermentation by working off the yeast and cleansing itself.
For white beer of superior quality, the temperature during
fermentation must not rise beyond 72° F. or 22·2° C.; some brewers
never allow it to exceed 18°C. (65° F.). The temperature is lowered by
means of a current of cold water, which circulates through a coil
fixed in the vats or other fermenting vessels.
In the case of porter, the initial heat of which is 64° F. or 17·8°
C., the temperature in the vats sometimes rises to 78° F. or 25·5° C.;
but such an increase in temperature excites considerable apprehension.
We have seen a tun for pale ale, containing 200 barrels of 36 gallons,
pitched with 600 lbs. of fairly solid yeast. In forty-six hours the
attenuation was considered sufficient, and the beer, which from an
initial heat of 58·1° F. or 14·5° C., had risen to 72° F. or 22·2° C.,
was cleansed to working casks. The large vats in which the
fermentation is started may be considered as equivalent to the _cuves
guilloires_ of French breweries, the casks in which it is completed
and the yeast thrown off representing their 75-litre vessels,
improperly called _quarts_. Notwithstanding the enormous English beer
manufacture, and although the fermenting vat, as in making porter, for
instance, sometimes attains the capacity of 2,000 to 3,000 litres (400
to 600 gallons), the casks into which it is run are never larger than
15 to 20 hectolitres (300 to 400 gallons); and even at Burton, in the
celebrated breweries of Allsopp and Bass, the pale ale is finished in
casks of a capacity less than 10 hectolitres, and yet the average
turn-out of these immense works reaches 3,000 to 4,000 hectolitres
(60,000 to 80,000 gallons) of beer per day.
Footnote 7:
[The expressions “high” and “low” fermentation or beer strictly refer
to temperature, whereas the other expressions used (“top” or “bottom”)
refer to the behaviour of the yeast. The French words _haute_ and
_basse_ seem to look both ways.—D. C. R.]
Footnote 8:
It is said that the floating cones or cylinders filled with ice, which
enable brewers to manufacture beer at a low temperature, even in
summer, were first used in Alsace.
Footnote 9:
45 million kilos. of ice are annually consumed in the brewery of M.
Dreher, in Vienna. The brewery of Sedlmayer, at Munich, uses about 10
million kilos. (_Journal des Brasseurs_, 22nd June, 1873.)
Footnote 10:
It should, however, be borne in mind that these remarks on the
relative preservative powers of the two beers hold true on account of
three things—differences in the respective modes of brewing,
artificial cooling during the process of fermentation, and the storing
of the “low beer” in ice-cellars. In itself, perhaps, “low beer” is
more liable to change than “high beer;” that this does not actually
take place, is due to the employment of artificial cooling. A brewery
which has an average annual production of 10,000 hect. will use 8,000
cwt. of ice. If we add to this the ice used during the retail of the
beer, which is best drunk at 12° C. (54° F.), we shall arrive at the
total of 100 kilos. per hectolitre.
Footnote 11:
[In connection with the comparison here instituted by M. Pasteur
between the drinking and keeping qualities of the two kinds of beer,
it may be useful to draw the reader’s attention to a review by Dr.
Charles Graham of the French edition of this work, published in
_Nature_ for January 11th, 1877, page 216. At the same time we must
remark that Dr. Graham appears to have overlooked M. Pasteur’s
footnote, page 12, English edition:—“His assertion, that by bottom
fermentation store beers can be produced, whereas those produced by
top fermentation must be consumed at once and cannot be transported,
are certainly strange to an Englishman. So far from these unfavourable
comparisons being true in all cases, the exact opposite is generally
the case. Bavarian and other bottom fermentation beers are in fact
those which can neither be preserved nor transported without the
liberal employment of ice; even that sent from Vienna to London must
be kept cold artificially, in order to avoid rapid destruction. As
regards flavour, there are many who think a glass of Burton pale ale,
or of good old College rent ale, to be superior to any Bavarian beer.
The chief cause of the decline in the production of top fermentation
beers on the Continent has been the want of attention in the
fermentation process; whereas the English brewer, especially the
brewer of high-class ales, has been unremitting in his attention to
the temperature in fermentation and to the perfect cleansing of the
ale. Now, where such attention is given, it is not difficult to obtain
ales which will keep a few years. While objecting to our English
produce being so hastily depreciated by M. Pasteur, our brewers will
be the first to avail themselves of his biological researches, in
order to render their produce more stable and better flavoured,
without having recourse to the general adoption of the vastly more
costly system of bottom fermentation.”—D. C. R.]
Footnote 12:
To preserve bottled beer from deterioration, some bottlers employ, at
the moment of filling, a small quantity of bisulphite of lime. Others
heat the bottles to a temperature of 55° C. (131° F.) In the north of
Germany and in Bavaria, this practice has been widely adopted since
the publication of the author’s “Studies on Wine,” and some of M.
Velten’s writings. The process has been termed _pasteurization_ in
recognition of the author’s discovery of the causes of deterioration
in fermented liquors, and of the means of preserving such liquors by
the application of heat. Unfortunately this process is less successful
in the case of beer than in that of wine, for the delicacy of flavour
which distinguishes beer is affected by heat, especially when the beer
has been manufactured by the ordinary process. This effect would be
less felt in beer manufactured by the process which is advocated in
this work.
Footnote 13:
A convincing proof of the influence of hops on the ferment organisms
is contained in the fact that beer, even after being raised to 60° C.
or 70° C. (140° or 160° F.), will, if unhopped, readily take on the
butyric fermentation, from which, if hopped, it would remain perfectly
free.
Footnote 14:
For historical details, see _l’Encyclopédie_, Art. _Bière_.
Footnote 15:
As a wine-producing country France has been highly favoured by nature,
but the consumption of beer in France is increasing every year. In
1873 the quantity of beer, paying excise duties, amounted to 7,413,190
hect., which yielded to the Treasury the sum of 20,165,136 fr. These
figures are taken from a report published in 1875 by M. Jacquème,
inspector of finances, who remarks that the quantity of beer upon
which excise duties are paid represents, probably, not more than
one-third of the total production: two-thirds of the quantity brewed
evades the duties.
CHAPTER II.
On the Causes of the Diseases which affect Beer and Wort.
From our preceding observations it will be evident that the manufacture
of beer, the arrangement of breweries, and all the processes practised
by the brewer immediately depend upon this fact, that beer and wort are
fluids essentially liable to change. Thus it becomes a matter of extreme
importance that we should have an exact knowledge of the causes and
nature of the changes which affect our produce, and it may be that this
knowledge will lead us to regard the conditions of the brewing industry
from a novel point of view, and bring about important modifications in
the practices of the trade. We might vainly search the numerous works
which have been written on brewing for information respecting the
proposed subject of these studies. At the most we should find the
diseases to which beer is liable in the course of its manufacture, or
afterwards, vaguely hinted at; perhaps we might be favoured with certain
empirical recipes for disguising the evil effects of those diseases.
It will be our endeavour to demonstrate the truth of the proposition we
have already laid down, that every change to which wort and beer are
liable is brought about solely by the development of organic ferments,
whose germs are being perpetually wafted to and fro in the dust floating
through the air, or distributed over the surface of the different
materials and utensils used in brewing, such as malt, yeast, water,
coolers, vats, tubs, casks, shovels, workmen’s clothes, and innumerable
other things.
It is evident that this proposition bears a marked resemblance to the
one which we have demonstrated concerning the diseases of wine.[16]
By the expression _diseases_ of wort and beer, we mean radical changes
which so affect the nature of those liquids as to make them unpalatable,
especially if they are kept; such changes produce beer which is sharp,
sour, turned, oily, putrid, and otherwise bad. It would be unreasonable
to apply the term _disease_ to certain modifications in the quality of
beer, which may be produced by practices more or less commendable. Such
modifications, too, may result from want of skill in the brewer, from
the composition of the wort, from the specific nature of the yeast, or
from the inferior quality of ingredients. It is a well-known fact that
“low beer,” if manufactured according to the ordinary process, has not
that same delicacy of flavour which characterizes beer fermented at a
lower temperature than 10° C. (50° F.). Fermented at 10° C. (50° F.), or
12° C. (53° F.) or at a higher temperature, it loses the peculiar
properties which consumers prize. Nevertheless, in point of soundness it
may be as good a beer as one which has been fermented at 6° C. (43° F.),
or 8° C. (46° F.). One might say of the former beer that it is inferior
to the latter in estimation; but we could not rightly call it diseased,
for we are supposing a case in which disease does not actually exist.
§ I.—Every Unhealthy Change in the Quality of Beer coincides with a
Development of Microscopic Germs which are alien to the Pure Ferment of
Beer.
Our proposition concerning the causes of the diseases of wort and beer
might be demonstrated in several ways. The following is one of the
simplest:—Take a few bottles of sound beer, say, for instance, that
which is known in Paris as Tourtel’s, Grüber’s, or Dreher’s, from the
name of the brewer who manufactures it. Place some of these bottles in a
hot-water bath and raise the temperature to about 60° C. (140° F.).
Permit them to cool, and then place them by the side of the other
bottles that have not been heated. In every case, especially if we
conduct this experiment in summer, we shall find that in the course of a
few weeks—the length of time varying according to the temperature and
the quality of the beer—all the bottles which have not been heated will
have become diseased, in some cases even to the extent of being
undrinkable. Let us next examine, by way of comparison, the deposits in
the heated and non-heated bottles. We shall find associated with the
pure alcoholic ferment other organisms, filiform and for the most part
very slender, and either simple or articulated, as represented in Plate
II., the design of which is taken from actual deposits occurring in beer
that had been kept for some time at the ordinary temperature. A number
of bottles of beer which had been heated on October 8th, 1871, were
compared with those of an equal number of bottles of the same beer which
had not been heated. The examination took place on July 27th, 1872. The
beer, which had been heated to 55° C. (131° F.), was remarkably sound,
well flavoured, and still in a state of fermentation. As a matter of
fact, we have proved by exact experiments that alcoholic ferments,
heated in beer, can endure a temperature of 55° C. (131° F.), without
losing the power of germination; but the action is rendered somewhat
more difficult and slower. Diseased ferments, however, existing in the
same medium, perish at this temperature, as they do in the case of wine.
The beer which had not been heated, had undergone changes which rendered
it quite undrinkable. Its acidity, due to volatile acids, was higher
than that of the other beer in the proportion of 5 to 1. The beer which
had been heated contained ½ per cent. of alcohol more than the other.
[Illustration: Plate 2. Appearance under the Microscope of the Deposit
from “Turned” Beer.]
The deposits in the heated bottles also showed filaments of disease, but
in such minute quantity that it was necessary to search many fields of
the microscope to discover their existence. Those which we found after
the heating must have existed in the beer before that operation; the
heat had destroyed them, without sensibly altering their shape or size;
they could neither multiply nor continue to exert any influence upon the
components of the beer.[17]
From these experiments we may easily perceive, on the one hand, that
beers apparently sound to the taste do not contain these or any other
filiform ferments, save in a scarcely appreciable quantity; and, on the
other hand, that these same ferments appear with the first unfavourable
change in the quality of the beers, and that they exist more or less
abundantly in proportion to the intensity of disease.
In certain extremely rare cases it may happen—so, at least, we have been
assured, but we have not proved the fact ourselves—that beer may keep
sound in bottle, even without the preliminary heating. This exception
can only occur in the case of certain beers of a peculiar composition,
which are highly hopped, and are made during the favourable months of
November or December, out of the choicest materials, and fermented with
yeast that happens to be pure. In the deposit of such beer, even after a
lapse of several months or several years, we should find only the
ordinary alcoholic ferment, the slow action of which would merely cause
a gradual increase in the quantity of alcohol existing in the beer, and
a diminution in the proportion of dextrine. This beer might grow old, as
wine does, and remain perfectly sound.
Very often the whole work of the brewer is jeopardized by the
unsuspected presence of diseased ferments, a remedy for which is only
devised after the evil has evoked the complaints of customers. In such a
case the brewer avails himself of the kindness of some other brewer to
obtain a change of yeast—a custom which is recognized and valued in the
trade, since all managers of breweries have an interest in keeping it
up. The brewer whose produce is most satisfactory recognizes the fact
that unforeseen circumstances may compel him at any moment to change his
yeast.
We have frequently had occasion to show that this necessity for a change
of yeast depends, in most cases, on some change brought about by the
presence of diseased ferments, the multiplication of which has resulted
fortuitously from some unconscious neglect during the process of
brewing, or from climatic influences. When we reflect that yeast is a
living being, and that the medium which serves as its aliment, and the
water in which it lives, are remarkably well adapted for the development
of a vast number of other microscopic beings, the comparative purity of
yeast should surprise us even more than its deterioration does.
Now by means of microscopical observations we might often detect the
existence of the evil long before we are warned of it by a defective
working, which invariably entails great losses.[18]
In proof of this remark we may cite the following facts. In the month of
September, 1871, we were permitted to go through a large London brewery,
in which the microscopical study of yeast was altogether unknown. We
were allowed to make certain experiments in the presence of the managers
of the establishment. We first examined porter yeast, which was
collected in a channel that received the yeast as it worked out of the
fermenting vessels. One of the ferments of disease abounded in this
yeast, as may be seen in the accompanying sketch, which was taken on the
spot (Fig. 1). It was evident that the working of the porter was
extremely unsatisfactory, and had, perhaps, been so for a long time;
indeed, we were told that they had obtained a change of yeast from
another London brewery that same day. We made a point of examining this
yeast with the microscope. It was beyond comparison purer than the
preceding yeast.
[Illustration: Fig. 1.]
It is evident that if these brewers had been in the habit of using the
microscope they might have detected the unsoundness of their produce
before the time when they actually made the discovery, which, no doubt,
was forced upon them by the complaints of their customers, or some other
annoying circumstance, that led to their obtaining a change of yeast.
We next obtained permission to examine the yeast of the other beers
undergoing fermentation, especially those of white beers, such as ale
and pale ale.
In the sketch which we made of these yeasts one may detect the presence
of the filaments peculiar to turned beer (Fig. 2).
[Illustration: Fig. 2.]
We examined with much interest the ales which had immediately preceded
those undergoing fermentation, the yeast of which we had just
inspected. We were furnished with two kinds, both in casks, the one
fined, the other not fined. The latter was visibly turbid, and,
examining a drop of it, we discovered three or four filaments present
in every field of the microscope. The ale which had been fined was
nearly clear, but wanting in brilliancy; it contained about one
filament to the field. We asserted in the presence of the head brewer,
who had been summoned, that these ales were extremely liable to
change, that it was highly necessary to dispose of them without delay,
and that they were necessarily already faulty in flavour—a fact which
all admitted after some hesitation—attributable, of course, to the
natural reluctance which every manufacturer feels to own that his
produce is not above reproach. We were shown some of the finings used
in the brewery; they were swarming with the same filaments of
disease-organisms.
We then propounded to the managers certain questions on the subject of
the losses which a brewery may sustain from changes in its beer. We had
heard from several brewers that the selling price of beer differed so
greatly from the cost of its production solely in consequence of the
losses which the unavoidable waste of large quantities of beer was
constantly causing; several brewers have in our presence estimated these
losses at 20 per cent. of the total production, on the average.
At first the English brewers returned somewhat vague answers to our
questions; however, after what had taken place, they doubtless
recognized the fact that a mutual understanding between a savant and a
practical man may often be of considerable benefit to the latter, and in
the end they confessed to us that they had stowed away in their brewery
a large quantity of beer which had gone bad in cask a fortnight or so
after it was brewed. Having avowed thus much they expressed their great
anxiety to learn the cause of so serious a change in their beer, which
was quite undrinkable. We examined it under the microscope, without
being able to detect immediately any diseased ferments, but being aware
that the beer had probably been clarified, by remaining undisturbed for
a very long time, and that these ferments might have become inert and
precipitated to the bottom of the enormous vats containing the beer, we
examined the deposits which had formed at the bottom of these vats. They
were composed solely of filaments of disease-organisms, without even the
least trace of the globules of alcoholic yeast. The supplementary
fermentation of this beer had evidently been nothing but a diseased
fermentation.
The resemblance between these filaments and those which, in considerably
smaller proportion, accompanied the globules of alcoholic ferment in our
preceding observations, the change in the beer, which was almost as bad
as beer could possibly be, along with an abundance of filaments, and the
change, to a minor extent, in that beer which only presented a few
filaments in a field of the microscope, impressed those managers of the
brewery who were present with an entire belief in the theory which we
had been endeavouring to impress on their minds concerning the causes of
the badness of their beer. Some eight days afterwards we paid another
visit to this same brewery, and learnt that the directors had lost no
time in acquiring a microscope, and in procuring changes of yeast for
all the varieties of beer, which they had put in working since our first
visit.
There are some periods of the year—early spring, summer, and autumn, for
instance—when the working of a brewery is a matter of great difficulty.
The preservation of yeast becomes a subject requiring the most delicate
treatment, in consequence of the increase in the temperature. In the
early part of autumn the most important ingredients used in brewing are
of inferior quality; the deteriorating influences which have been at
work have covered them with a variety of parasites. All these
circumstances contribute to facilitate the development of diseased
ferments.
§ II.—The Absence of Change in Wort and Beer Coincides with the Absence
of Foreign Organisms.
The method which we have just pursued in demonstrating the existence of
a relation between the diseases of beer and certain microscopic
organisms can scarcely leave a doubt, it seems to us, as to the
correctness of the principles which we are advocating. In every case
where the microscope reveals in a yeast, especially a yeast which is in
a state of activity, products which are foreign to the composition of
alcoholic ferment, properly so called, the flavour of the beer is more
or less unsatisfactory, according to the abundance or nature of these
minute organisms. Moreover, when a finished beer of superior quality
loses in the course of time its agreeable flavour, and becomes sour, it
may readily be shown that the alcoholic ferment in the deposit existing
in bottles or casks, although originally pure, at least in appearance,
becomes gradually intermixed with these same filiform ferments or other
ones. These facts may be deduced from what precedes; nevertheless, some
prejudiced minds might perhaps urge that these foreign ferments are the
consequence of some diseased condition, produced by circumstances of
which we know nothing.
Although this gratuitous supposition may be difficult to sustain, we
shall endeavour to corroborate our preceding observations by the method
of experiment which will be seen to be the more decisive.
This method consists in proving that beer never possesses any unpleasant
flavour, so long as the alcoholic ferment, properly so called, is not
associated with foreign ferments; that this also holds good in the case
of wort, and that wort, liable to change as it is, may be preserved in a
state of purity, if it is kept under conditions that protect it from the
invasion of microscopic parasites, to which it presents not only
favourable nutriment, but also a field for development.
By employing this second method we shall, moreover, have the advantage
of proving with certainty a proposition that we just advanced, and
showing that the germs of these organisms proceed from the particles of
dust which the common air wafts about and deposits on every object, or
which are spread over the utensils and materials used in a brewery,
materials that are naturally charged with microscopic germs, which
various changes in the store-houses and maltings may multiply to an
indefinite extent.[19]
[Illustration: Fig. 3.]
Let us take a glass flask having a long neck (Fig. 3 A), and holding
from 250 c.c. to 300 c.c. (_i.e._, about 9 or 10 fl. oz.); let us put
into it some wort, hopped or not, and then draw out the neck of the
flask in the flame of a lamp, so as to give to it the shape B (Fig. 3);
let us next heat the liquid to the boiling point, when the steam will
rush with a hissing sound out of the curved end. We may then, without
further precaution, permit our flask to cool, or, as an additional
safeguard, we may introduce a small quantity of asbestos into the open
extremity, at the very moment when the flame is taken away from the
flask. Before introducing the asbestos, we may pass it through the
flame, and we may repeat this after it has been placed in the end of the
tube.[20] The air which first re-enters the flask must come in contact
with the heated glass and the hot liquid, and these will destroy the
vitality of any germs existing in such particles of dust as this air may
introduce. The re-entrance of the air will be effected very
gradually—sufficiently so to enable the drop of water which the air, as
it enters, forces up the curved tube, to catch all particles of dust.
Ultimately, the tube will become dry, but then the passage of the air
will proceed so slowly that every foreign particle will get deposited on
its interior sides.
Experience tends to prove that external particles of dust cannot find
their way into flasks of this pattern, having free communication with
the air, at all events within ten or twelve years—the longest time that
has been devoted to experiments of this kind; the liquid in the flasks,
if originally clear, will not become in the least degree contaminated,
either upon its surface or throughout its bulk, although the outside of
the flasks may be covered with a thick coat of dust. This is an
undeniable proof of the impossibility of particles of dust finding their
way inside such flasks.
Wort treated thus will preserve its purity for an indefinite time,
notwithstanding its extreme liability to rapid change when exposed to
the air, under conditions which cause it to come in contact with the
particles of dust that air contains. This also holds good in the case of
wine, beef-tea, the must of grapes, and, generally speaking, of all
liquids which are subject to putrefaction or fermentation, and which
possess the faculty, when their temperature is raised to about 100°C.
(212°F.), of destroying the vitality of those microscopic germs that are
found in dust.
A flask such as we have described (Fig. 3) is all that we require when
we have to demonstrate the facts that we have just reviewed, a more
detailed account of which may be found in our Memoir published in the
_Annales de Chimie et de Physique_, for 1862, under the title _Mémoire
sur les corpuscules organisés en suspension dans l’atmosphère. Examen de
la doctrine des générations spontanées._ The shape of the flask
represented in Fig. 4 only differs from that of the preceding one in
having a second little tube attached to the globular part of the flask;
this presents great advantages for different objects of study, and it
was adopted in the subsequent investigations detailed in this work.
This flask will permit us to study without difficulty every separate
kind of microscopic organism in the liquid best adapted to it without
fear, if we take reasonable precautions, that the subject of our study
may become associated with other organisms, the accidental presence of
which cannot fail to seriously affect the results of our observations.
Let us use one of those flasks in our experiment on yeast, at the same
time expressly assuming that the minute germs of yeast are free from all
contamination by foreign germs, an object which we shall learn how to
realize by a variety of methods in a subsequent chapter.
[Illustration: Fig. 4.]
Let us introduce some wort into our flask (Fig. 4); then, after we have
fitted an india-rubber tube to the little supplementary tube, let us
boil the liquid; the steam, finding an easier exit through the
india-rubber opening than through the drawn-out tube, will rush out
through the india-rubber tube, and thus, as it passes, destroy any germs
which may be adhering to the sides of the little supplementary tube. If
we close the india-rubber tube by means of a glass stopper, the steam
will immediately issue through the bent tube. On permitting the flask to
cool, it will then be ready for impregnation. If there were any fear
that some foreign germ of an unknown nature might have effected an
entrance during cooling, or had not been destroyed by the steam (which
is always a little super-heated, in consequence of the resistance which
it meets in escaping), we need only place the flasks on a warm stove,
and leave them there for a few days or a few weeks to ascertain whether
the liquid in them has undergone any change. We should then only use
those flasks which contain a sound liquid.
At the same time we must warn our readers that this cause of error does
not exist once in a thousand times, especially if we use an asbestos
stopper to prevent the entrance of little insects which are attracted by
the odour of the liquid, and which instinctively seek to enter at the
extremity of the tube, and to pass through it into the flask. In going
so far, and incurring such labour in search of their food, they condemn
themselves to certain death, for they are sure to be drowned, since it
would require an intelligence superior to that which they possess to
enable them to get out of the flask; the liquid, morever, could not fail
to undergo some change, in consequence of the particles of dust that the
insects would introduce into it.
After having passed the flame of a spirit-lamp quickly over the
india-rubber tube, the glass stopper, the curved tube, and even over the
fingers of the operator, we may withdraw the glass stopper, and
introduce the pure yeast by means of a glass pipette that has been
previously heated. This yeast is kept in a vessel also free from the
dust floating in the air. However few globules of yeast the glass tube
may take up, it is sure to introduce a hundred or a thousand times more
than is necessary for the impregnation of the liquid. The glass stopper
must then be replaced immediately, after having been again quickly
passed through the flame. In transferring our yeast from the vessel
containing it to the flask, by means of a glass pipette, it is exposed
to another cause of impurity, since we cannot avoid bringing it in
contact with the common air. If this risk frequently troubled us in our
experiments, we might banish it or minimize it by some new arrangement;
but this is unnecessary. We have suffered no inconvenience from this
cause, as there does not exist in the atmosphere anything like a
continuous supply of that from which the so-called _spontaneous_
generation arises, as was erroneously believed to be the case before the
publication of our Memoir in 1862, to which we have already alluded.
The following are the results of the experiments conducted in the manner
just described.
The yeast which we sowed, in ever so small a quantity, seemed to acquire
vigour, to bud, and to multiply. Soon, that is to say in the course of
twenty-four or forty-eight hours or longer, according to the
temperature, and, more especially, the degree of vitality in the
globules, we found that the sides of our flasks were covered with a
white yeasty deposit, and noticed on the surface of the liquid a fine
froth, which at first appeared like little islets formed by groups of
bubbles so minute that they would have been imperceptible had they not
been joined together. These patches increased in size, and gradually
attached themselves to each other, finally forming a thick froth. In the
course of two or three days this froth fell, the fermentation proceeded
less rapidly, and then ceased completely. The beer was finished. This
beer might be preserved for an indefinite period in the flask without
undergoing any change. The external air passes freely into and out of
the flask, as the pressure of the atmosphere and the temperature vary,
and the beer in the course of time becomes flat; it acquires age in much
the same manner as wine does, but it never contracts any taste of
disease, it never becomes sour, or sharp, or bitter, or putrid; it does
not even become covered with _mycoderma vini_ as is usually the case
with all beer exposed to the common air in the course of trade.
After some weeks, or perhaps months, a white ring may show itself on the
surface of the liquid on the glass. This is a crown formed by a mass of
young yeast globules, which grow there like a mould, by absorbing the
oxygen of the air as it enters the flask. The bulk of the yeast which
has been fermenting remains at the bottom of the liquid in the form of
an inert deposit. This inertness, however, is apparent rather than real;
the globules may be internally active, without any development of new
buds, and the effects of this working may cause them to become more and
more languid, and in the course of time may even destroy them.
The case is quite different when the yeast with which our wort is
impregnated, instead of being pure, is mixed to any extent whatsoever
with diseased ferments. Should there be any of these in the yeast with
which we impregnate our wort, even though their quantity were so
infinitesimal that the most skilful observer could scarcely discover
them with the microscope, they would multiply in the flask after the
beer had been finished, especially if the beer were left for a short
time on a stove. In this manner we may secure an excellent test of the
original purity of the yeast which we employ in the impregnation of our
wort.
Thus it may be seen that the absence of microscopic organisms that are
foreign to the nature of pure yeast may invariably be noticed in the
case of a beer which is sound, and which will remain sound for any
length of time, when in contact with pure air, at any temperature. We
may see, too, that the presence of these organisms may invariably be
detected in an unsound beer, the peculiar unsoundness of which depends
upon the peculiar species of the organisms contained in it. It would be
difficult to adduce clearer proofs than those which we have given as to
the intimate relation existing between these organisms and the
deterioration of beer. The relation between cause and effect, in the
succession of physical phenomena in general, is established by proofs
that are by no means more decisive.
Footnote 16:
A statement of this proposition, as far as it concerns beer, appeared
first in outline in the author’s _Etudes sur le vin_, published in
1866.
Footnote 17:
As the deposit in the heated bottles is, as a rule, inconsiderable, it
is necessary to exercise some precaution in collecting it. The bottles
are taken up; after some days’ rest they are decanted very carefully,
with as little shaking as possible, until not more than one or two
cubic centimetres (about a tea-spoonful) of the liquid remains at the
bottom. The bottles are then shaken vigorously, with the object of
collecting the whole of the deposit from the bottom and the sides into
this small quantity of liquid; a drop of this is then examined under
the microscope.
Footnote 18:
Since the publication of the author’s “Studies on the Diseases of
Wine, and the Dangers resulting to Wine and Beer from the Microscopic
Parasites found therein,” some intelligent brewers have derived
considerable profit from the application of the theories laid down in
that work.
Footnote 19:
If we put a handful of germinating barley from a maltster’s cistern
into a little water, and examine drops of the liquid, after it has
become turbid, under a microscope, we shall be amazed at the wonderful
number of strange microscopic organisms that swarm on the surface of
the grains and on the sides of the cistern. There is no doubt that
their presence is injurious to germination, inasmuch as they absorb
much oxygen; moreover, they acidify the grain and cause it to
deteriorate.
Footnote 20:
In these experiments the asbestos is only introduced by way of extra
precaution. Originally, in his early experiments in connection with
the subject of spontaneous generation, the results of which were
published in 1860-62, the author did not use it, and he observed no
ill effects resulting from the omission; now, however, he constantly
makes use of it. In studies of this kind novel precautions are never
thrown away; moreover, the presence of this asbestos is a sure bar to
the entrance of insects. The author has preserved for a long time a
flask, in the slender neck of which an insect is contained; he killed
it with a flame just as it was approaching the liquid. Quite recently,
M. Calmettes, a young engineer from the École Centrale, when engaged,
at Tantonville, in Tourtel’s brewery, in carrying out certain
practical experiments in connection with the process that will he
described in one of the later chapters of this work, wrote complaining
that his flasks had been suddenly invaded by a swarm of aphides,
scarcely larger than phylloxeras, and that many of them had even
penetrated into the inside of the curved tubes.
CHAPTER III.
On the Origin of Ferments properly so called.
The new process of brewing, which it is the principal object of this
work to explain, and which will follow as an immediate and inevitable
deduction from the novel facts herein demonstrated, cannot be fully
understood without a knowledge of all the principles upon which it is
founded. One of the most essential of these has reference to the purity
of our fermentation. We should gain but little from the use of a yeast
uncontaminated by any foreign germs if natural organic substances had
the power of organizing themselves by means of spontaneous generation,
or by some transformation which took place amongst them, or even by a
conversion of certain microscopic beings into certain others. Theories
of this kind are still warmly advocated, but, to our thinking, rather
from sentimental considerations or prejudice than from any basis of
serious experimental proofs.
Be this as it may, we must free our minds from all suppositions which
might qualify the exactness of the principles upon which our new process
is founded, or cause any doubt in the minds of our readers as to the
possibility of its application and the benefits to be derived from its
adoption.
§ I.—On the Conditions which cause Variations in the Nature of the
Organized Products existing in Infusions.
We have proved by experiment, in the preceding chapter, that a few
minutes’ boiling renders liquids, and more especially wort, absolutely
free from liability to change when in contact with pure air, that is,
air which contains none of the germs of organisms that are continually
floating about in the atmosphere.
What is true in the case of wort is equally so in the case of all
organic liquids; there is not a single one that could not be rendered
inaccessible to any subsequent change if it were brought, first of all,
to a suitable temperature, which would vary with the nature of the
liquids. Amongst them there are some which, like vinegar, lose their
tendency to change after having been rapidly raised to a temperature of
not more than 50° C. (122° F.); others, like wine, require a greater
heat. Wort, to which no hops have been added, should be subjected to a
temperature of not more than 90° C. (194° F.); milk to about 110° C.
(230° F.).[21]
It is easy to show that these differences in temperature, which are
required to secure organic liquids from ultimate change, depend
exclusively upon the state of the liquids, their nature, and, above all,
on the conditions that affect their neutrality, whether towards acidity
or alkalinity; for it is not difficult to observe that the least changes
in these respects lead to considerable variations in the temperatures
which we must employ.[22] We could adduce many examples of this. The
only difference between the nature of must and that of wine is caused by
fermentation. We may say the same thing of wort and beer, and, better
still, of new milk and sour milk. Must, to be secured from change,
requires a much higher temperature than wine does; similarly, wort
requires a much higher temperature than beer. Milk must be heated to
about 110° C. (230° F.), as we have just stated, but sour milk would
require 20° C. or 30° C. (36° F. or 54° F.) less. Wine, when fresh,
ceases to be liable to change after it has been brought to a temperature
below 100° C. (212° F.); it requires a temperature of more than 100° C.
in the presence of carbonate of lime.
As regards the explanation of the influence which acidity or alkalinity
exerts in diminishing or increasing the temperature required to protect
infusions and organic matters from ultimate change, although this is a
subject which claims special study, we are inclined to believe that
acidity permits, and alkalinity prevents, the penetration of moisture
into the interior of the cells of the germs belonging to infusions, so
that in heating the outer cases of these cells in an alkaline medium we
heat the germs in a dry state; and in heating the outer cases in an acid
medium we heat the germs when they are moist. We all know that these
conditions make a great difference in the resistance which bodies offer
to the action of heat. A particle of mould which, in a moist state,
cannot survive a temperature of from 60° C. to 100° C. (140° to 212°
F.), will preserve its fecundity even if heated to 120° C. (248° F.), if
it has been previously well dried.[23]
The nature of the spontaneous productions which we see appear in organic
liquids is affected to a remarkable extent by the smallest change in the
compositions of those liquids. Generally speaking, as we have often
proved in our former works, a feeble acidity is unfavourable to the
development of bacteria and infusoria, and, on the other hand,
favourable to the growth of mould. A liquid which is neutral or of
feeble alkalinity behaves in an exactly inverse manner.
Those who support the theory of spontaneous generation seek to find in
the natural differences between the organic productions of various
liquids which are simultaneously exposed to the same atmosphere, an
argument in favour of their doctrine. These differences, however, are
only an effect of the greater or less fitness of a peculiar liquid for a
certain kind of growth. When an acid organic liquid, such as the must of
grapes for example, is exposed freely to the air, it is besieged
simultaneously by spores of _mucedines_, as well as germs of _bacteria_,
_leptothrix_, _vibrios_, _&c._, but the latter germs are checked in
their development, if, indeed, they are not actually destroyed, by the
acidity of the liquid; and we should never find them there in their
adult state.
Most moulds, on the other hand, thrive in acid liquids, and therefore
they are generally found alone. If we began by saturating must with
carbonate of lime, previously dried or otherwise, we should observe
opposite phenomena; bacteria, lactic ferments and butyric vibrios would
invade our fields long before the spores of mould had time to grow,
since the germination of these proceeds very languidly in neutral or
alkaline liquids, and an infusion once occupied by a living organism has
much trouble in nourishing others; the early developments consume the
alimentary substances, especially the oxygen.
Differences as marked as these in the adaptability of certain liquids to
certain growths give rise to innumerable illusions, and are one of the
chief sources of error in the study of this subject. If we sow in an
acid liquid, such as must, an alcoholic ferment, the development of
which is not arrested by the acid character of our medium, it will
multiply there, and we shall have no difficulty in growing it over and
over again in the same acid medium. This being the case, let us suppose
that our alcoholic ferment is impure—let us say, mixed with filaments of
turned wine, which are due to a ferment checked in its development by
the peculiar qualities of the must. In repeating the growth of this
alcoholic ferment in the must the filaments which were, by supposition,
present in our first sowing, and which cannot reproduce themselves in
the must, or do so with great difficulty, will become very scarce in the
fields of our microscope; they will not, however, cease to exist, for
the repetition of our attempts to grow them only serves to spread the
original germs over a larger surface; and, although the eye fails to
detect them, they will only have become more difficult to discover. At
this point the experimentalist is in danger of falling into error, for
when he no longer perceives the foreign ferment he will be inclined to
believe that it has vanished, and that he may regard the alcoholic
ferment as being free from all impurity, without testing for the purity
by a direct experiment.
An example of this mistake is to be found in a recent work by M. Jules
Duval. This writer has published a theory according to which yeast
becomes transformed into lactic ferment, and likewise into other
ferments—that of urea, for example—the only condition of change,
according to M. Jules Duval, being that we should cultivate it in
suitable mediums. The proofs by which he supports his conclusion are
altogether inadmissible, and a simple glance at his experiments enables
us to detect innumerable causes of error. M. Duval believes that yeast
becomes transformed into lactic ferment from the fact that he obtained a
fermentation which furnished lactate of lime and lactic ferment from
some sour milk to which he had added some glucose, chalk, and phosphate
of ammonia before impregnating it with yeast; but he took no steps to
secure himself against introducing into his medium—which was, as a
matter of fact, well adapted to lactic fermentation, inasmuch as it was
a little alkaline—an alcoholic ferment containing impurities. This was
the crucial point in his experiments. M. Duval recognizes this, but he
deceives himself when he says, without proof:—“My alcoholic ferment is
pure, for I have grown it over and over again in must, preserved in
flasks prepared after the manner of those which M. Pasteur uses in his
experiments.” Here we have merely a simple assertion; a direct
experimental test might have proved that the yeast was impure.
Yeast cannot transform itself into lactic ferment. No matter what the
medium may be in which it is sown, _if it is actually pure_ it will
never present the least trace of lactic ferment or of any other
ferments. By certain changes in the nature of the medium, the
temperature, and other conditions, the cells of the ferment may become
oval, elongated, spherical, and larger or smaller in size, but they will
never produce the most minute quantity of lactic ferment or lactic acid.
The whole theory of the transmutation of ferments, which M. Duval has
published, is imaginary.[24]
We have asserted that the source from which we obtain our supply of the
substances that we expose to contact with the air may likewise furnish a
reason for the development of vegetable or animal organisms which make
their appearance in our infusions. This may be easily understood. If we
expose the infusions to temperatures more or less high, with the object
of destroying the vitality of the germs which they may contain, we
completely suppress all germs originating from two different
sources—those which the infusions may have acquired directly from the
atmospheric air, or from the dust upon our utensils, and those which may
have been introduced by the materials used in manufacturing our
infusions or decoctions, which materials must have been brought from
some distance. An infusion, after having been heated to a sufficient
degree, can harbour and nourish only such germs as are conveyed to it by
the air after the heating. These floating germs are far from being as
varied in their nature as it pleases those to believe who are tied down
by their arbitrary and faulty interpretation of the knowledge that we
have acquired, and the discussions in which we have taken part, during
the last fifteen years. Air, unless in violent agitation, can hold only
the most minute particles in suspension. The observations which have
been recorded concerning organisms of spontaneous growth found in
infusions, have always been made in sheltered places—in rooms or
laboratories, the atmosphere of which is, relatively speaking, very
still. For this reason, in liquids that have been subjected to heat, the
_flora_ and _fauna_—if we may use such an expression—are very poor, and
all the more so because, as we have recently had occasion to remark, a
great number of the organisms which would spring into existence of their
own accord, if they were allowed sufficient time for germination, are
kept back by others of a more rapid development. The truth of this is
evident from the fact that we may observe greater variations in the
nature and number of species of living organisms, if we divide one
infusion amongst several vessels which are immediately closed up again,
than if we leave our infusion in contact with an unlimited volume of
surrounding air. By this means we expose each portion of the liquid to
no other germs than those existing in a state of suspension in the
volume of air introduced into the vessels; and it so frequently happens
that we obtain a variety of germs which, coming into contact with a
liquid adapted to their nutrition, without having mixed with others,
finally multiply there, in consequence of no other organisms of greater
activity occurring to impede their slow and laborious propagation.
The nature of the products resulting from raw infusions—that is, those
obtained, without heating, from the maceration of organic substances,
such as leaves, fruits, grains, or the organs of plants or animals—is
much more varied. The reason of this is that such substances generally
carry with them not only the particles of dust existing in air that is
in motion, but also microscopic parasites, which find a congenial
resting-place on their surface or its vicinity. We may cite a few
accurate observations on this point, for the subject is one of great
interest.
If we boil an infusion of hay, and then expose it to contact with the
air in a room, all its productions will be derived from such germs as a
comparatively still air can carry about; thus, we shall very rarely find
any _colpoda_ in our infusion, for the germs of these infusoria,
consisting of rather large cells, can scarcely exist in a state of
suspension in motionless air, in spite of their extraordinary diffusion
in nature. On the other hand, we almost invariably find _colpoda_ in
macerations of raw hay. This difference is easily accounted for; the
particles of dust adhering to the surface of hay, especially that which
comes from marshy districts, contain the germ-cells of _colpoda_ in
abundance. The reason is obvious; rain falls on a meadow and forms
little pools of water about the roots of the herbs that grow there; this
water remains for some time, and very soon swarms with a multitude of
infusoria, especially _colpoda_. Dryness follows; the _colpoda_ becomes
encysted, and forms a dust that is wafted by the winds on to the blades
of grass, so that the mower will carry away not only his hay, but also
myriads of _colpoda_, as well as spores of _mucedines_ and other
organisms.[25]
The maceration of pepper will give us some infusoria hardly ever found
in other infusions, the reason of this being that such infusoria exist
where the pepper grows—in other words, their germs are exotic. That the
infusion of a special plant should give us special infusoria, is
scarcely more surprising than the discovery of a particular parasite or
insect existing on a particular plant, and not on others of a different
species that grow near it. Thus it happens that the ferment-germs of
must exist on the surface of grapes, whether detached or in clusters. It
is only natural that we should find the organ or the plant that is
destined later on to become the food of a parasite serving as a
habitation for the germs of that parasite.
§ II.—Experiments on Blood and Urine taken in their Normal State, and
Exposed to Contact with Air that has been Deprived of the Particles of
Dust which it Generally holds in Suspension.
Recourse to the application of heat, in the first place, is an excellent
means, as we have just seen, of procuring organic liquids free from all
disturbing germs; but there is a still more remarkable and instructive,
we may even say more unlooked for, method of securing this result, which
may be described as in some measure borrowed from the nature of things.
It consists in seeking purity in the natural liquids of animals and
plants. It is difficult to understand how the liquids circulating in the
organs of animal bodies, such as blood, urine, milk, amniotic fluid, and
so on, can possibly secrete the germs of microscopic organisms. There
would be excellent opportunities for these germs to propagate themselves
if they actually did exist in the liquids appertaining to the animal
economy. Life in all probability would become impossible in the presence
of such guests. A proof of this is to be found in the multitude of
diseases which many of the greatest minds of modern times attribute to
parasitic developments of this nature. Medical men of high authority
agree in thinking that the questions of contagion and infection will
find solutions from the obscurity in which they are now involved in a
careful study of ferments, and that hygienists and physicians should
labour to secure by every possible means the destruction of the germs of
ferments, and should strive to check _their_ development, and prevent
the evils which _they_ cause when developed. Great progress has already
been made in this direction, and we deem it a signal honour that our
researches on the subject have been considered, even by those by whom
this progress has been accomplished, as the source from which they
derived their first inspirations. We shall, doubtless, be excused by our
readers if we recall this fact in relating certain historical details
which are especially necessary in order that they may comprehend the
principles that we are endeavouring to explain in these “studies.”
It is a matter of regret to us, however, that the facts which we have
established should have been accredited with any importance beyond that
which is their due. The exaggeration of novel ideas invariably leads to
a reaction, which, again, overshooting the mark, brings into disrepute
even those points in which such ideas are perfectly just, or, at all
events, worthy of serious consideration. There are certain symptoms of
such a reaction in the case of our theories: they are evident in the
tendency of unreflecting minds to give a total denial to the fact that
certain diseases may be derived from certain ferments—organized and
living ferments—of the nature of those which have been discovered in the
course of the last twenty years. We should be guided by facts, whichever
side of the question we espouse, and by facts alone we should test the
truth of doubtful discoveries. We are but on the threshold of the
exploration of our subject, and we should strive to discover new facts
in connection with it, and should deduce from these, whatever they may
be, only such conclusions as they may strictly warrant. Unfortunately,
there is amongst physicians a tendency to generalize by anticipation.
Many of them are men of rare natural or acquired talent, endowed with
keen powers of intellect, and the art of expressing themselves fluently
and persuasively; but the more eminent they are, the more they are
occupied by the duties of their profession, and the less leisure they
have for the work of investigation. Urged on by that thirst for
knowledge which belongs to superior minds, and perhaps, in some measure,
through associating with the upper classes of society, which are
becoming more and more interested in science, they eagerly seize upon
easy and plausible theories, readily adapted for statement which is
general and vague just in proportion to the unsoundness of the facts on
which they are based. When we see beer and wine undergo radical changes,
in consequence of the harbour which those liquids afford to microscopic
organisms that introduce themselves invisibly and unsought into it, and
swarm subsequently therein, how can we help imagining that similar
changes may and do take place in the case of man and animals? Should we,
however, be disposed to think that such a thing must hold true, because
it seems both probable and possible, we must, before asserting our
belief, recall to mind the epigraph of this work: _the greatest
aberration of the mind is to believe a thing to be, because we desire
it_.
One of the most distinguished members of the Academy of Medicine, M.
Davainne, who was the first to give his attention to rigorous
experiments on the influence that organic ferments exercise on the
production and propagation of infectious diseases, declares that the
idea of his researches on _splenic fever_ and _malignant pustule_ was
suggested to him by his perusal of our work on butyric fermentation,
published in 1861. In 1850 this gentleman and M. Rayer discovered in the
blood of animals attacked by these diseases minute filiform bodies, to
which they paid little attention, and which M. Davainne recollected,
when he came across our Memoir. He had the foresight to conjecture—a
conjecture that was soon confirmed most decisively by his
researches—that the former disease, known under the name of _sang de
rate_, might be the production of a fermentation analogous to the
butyric, in which the minute filiform bodies observed by Rayer and
himself, in 1850, played the part which vibrios fill in butyric
fermentation. Within two years of this the first works of Messrs. Coze
and Feltz appeared. These clever and courageous experimentalists avowed
that their beautiful researches had been suggested to them by the
perusal of my work on putrefaction, published in 1863. We might also
quote the striking and admirably conceived experiments of Dr. Chauveau,
on castration.[26] We cannot, however, refrain from reproducing here a
letter addressed to us in 1874 by the celebrated Edinburgh surgeon, Mr.
Lister:—
“Edinburgh, Feb. 10, 1874.
“DEAR SIR,—Will you permit me to beg your acceptance of a pamphlet
which I forward to you by this post, and which describes certain
inquiries into a subject upon which you have thrown so much
light—the theory of germs and fermentation? It gives me pleasure to
think that you will peruse with some interest what I have written
about an organism that you were the first to study in your Memoir on
lactic fermentation. I do not know if you ever see the records of
British surgery. If you have perused them you may have observed from
time to time notices of the antiseptic system which I have been
endeavouring for the last nine years to bring to perfection. Permit
me to take this opportunity of offering you my most hearty thanks
for having demonstrated by your brilliant researches the truth of
the theory of putrefactive germs, and for having afforded me in this
manner the sole means of perfecting the antiseptic system.
“Should you ever come to Edinburgh I am sure that you will be truly
gratified to see in our hospital the extent to which the human race
has profited by your work. I need hardly add, that I should have
great satisfaction in showing you how greatly surgery is indebted to
you.
“Excuse the freedom which I have taken in addressing you, on the
grounds of our common love for science, and believe in the profound
esteem of yours, very sincerely, JOSEPH LISTER.”
The wad dressing of Dr. Alphonse Guérin, surgeon at the Hôtel-Dieu,
Paris, which has already rendered great assistance to surgery, and has
been the subject of a very favourable report at the Academy of Sciences
in Paris, was invented by its author in consequence of certain
reflections suggested to him by the perusal of our researches. The
commission which framed the report made, through M. Gosselin, some wise
reservations in the case of certain theoretical ideas which M. Guérin
had not sufficiently proved by experiment. We have no doubt, however,
that when the matter is thoroughly examined, facts will confirm the
truth of the wide views entertained by the surgeon of the Hôtel-Dieu.
Dr. Déclat has founded quite a new system for the treatment of
infectious diseases, which is based upon the use of one of the best
known antiseptics, phenic acid. His theory, which he affirms was
suggested to him by our studies on fermentations, is, that the diseases
which transmit themselves are, each of them, the product of a special
ferment, and that both medical and surgical professors of therapeutics
should make it their study to prevent exterior ferments from penetrating
into the liquids of our economy, or in the event of these ferments
having found their way into the system, to discover _antiferments_ for
their destruction, without effecting any change in the vitality of the
histological elements of the liquid or tissues.
There is no doubt that extreme caution must be exercised in dealing with
questions of this kind, as M. Sédillot has authoritatively remarked; but
at the same time it cannot be denied that the more such questions are
discussed with exactness, the more those celebrated practitioners who
originated them are confirmed in the ideas which first guided them. We
may give another example of this.
In 1874, in consequence of a communication addressed to the Academy of
Sciences by Messrs Gosselin and A. Robin, on the subject of ammoniacal
urine, we made the observation that we should endeavour to ascertain if,
in all such cases, the urinary fluids were not rendered ammoniacal by
the presence of the little ferment of the urea, which we have previously
noticed,[27] and which has since then been discussed with remarkable
intelligence by M. Van Tieghem, in the thesis which he maintained for
his doctor’s degree. The suggestion and the considerations that
justified it led to a discussion before the Academy of Medicine, in
which contrary opinions were maintained. We lost no time in submitting
these to the test of facts. We could not find a single person suffering
from ammoniacal urine, in whose case the little ferment which we
mentioned was not to be detected. Our predictions were thus completely
justified.
As early as 1864 the _Gazette Hebdomadaire de Médecine et de Chirurgie_
published an account of urine made ammoniacal in the bladder, the author
of which, Dr. Traube, makes the following observations:—“It was believed
that, in consequence of the retention of the liquid, and the resulting
distension of the bladder, that organ became irritated and produced a
larger quantity of mucus, and that this mucus was the ferment which
caused the decomposition of the urea, by virtue of a chemical action
peculiar to itself. This belief can no longer be held in presence of M.
Pasteur’s discoveries. This observer has demonstrated, in the most
conclusive manner, that ammoniacal fermentation, like alcoholic and
acetic, is produced by living beings, whose pre-existence in the
fermentable liquid is a necessary condition of the process. The
preceding fact offers a remarkable proof of M. Pasteur’s theory. In
spite of the long duration of the retention, alkaline fermentation was
not produced by an excessive secretion of the vesical mucus or of pus:
it only began from the moment when the germs of vibrios passed from the
outside into the bladder.”[28]
Finally, we may conclude with perfect truth that the liquids of our
economy, blood and urine, for instance, may afford a harbour to
different ferments, even in the inmost parts of the organs, when
external causes enable such ferments to find their way into those
liquids, and that diseases of greater or less gravity result from this
cause. On the other hand, it must be admitted that the bodies of animals
in a state of health afford no means of entrance to these external
germs. At the same time, direct experiment alone can convince the mind
as to the truth of this latter assertion. Let us take some of the
substances that are to be found inside living animals in perfect health,
and expose them, in the same condition in which life has formed them, to
contact with pure air.
[Illustration: Fig. 5.]
[Illustration: Fig. 6.]
For this purpose we must provide ourselves with a glass flask, joined to
a copper tap by means of an india-rubber tube, as shown in Fig. 5. The
two branches of the tap should be about twelve centimetres long (about
½-in.), the one which is free tapering off like the end of a pipe. In
order to destroy all germs which may exist in the flask, we must join
the free end of the copper tube to a platinum tube kept at a very high
temperature, after having carefully introduced into the flask a small
quantity of water, and expelled all the air by converting the water into
steam. Then as we allow the flask to cool, the air which re-enters it
will necessarily pass through the hot tube (Fig. 6).
[Illustration: Fig. 7.]
We may cause the water in the flask to boil at a temperature of more
than 100° C. (212° F.) by fitting to the free end of the platinum tube a
glass tube bent at right angles, which we plunge to any depth in a deep
vessel filled with mercury (Fig. 7). Whilst the water is boiling under
pressure, we must separate the tube which is plunged in the mercury; the
water in the flask will continue to boil at the ordinary pressure. We
must then leave the flask to cool. It will gradually become filled with
air that has been heated to a high temperature, more than sufficient to
burn up all the organic particles of dust which that air could have
contained. When the flask is cold we must close the tap and detach it,
and proceed to prepare other similar flasks. It will be advisable to
close the tap when the temperature of the flask is still a few degrees
above that of the surrounding atmosphere: this precaution will cause the
air in the cooled flask to have a lower pressure than that of the
external atmosphere.
During the interval which must elapse between the preparation and the
use of a flask, it is a good thing to keep the free branch of the tap
inclined towards the ground, to secure the inside of its tube from the
deposit of external particles of dust. Whether this precaution be
adopted or not, we must take care to heat this branch in the flame of a
spirit lamp just before we bring our flask into requisition.
If we have to study blood, we must take it from a living animal—a dog,
for example. We must expose a vein or an artery of the animal, and make
an incision into which the end of the free tap-branch, which has
previously been heated and allowed to cool, must be introduced and fixed
by a ligature in the vein or artery. On opening the tap, the blood will
rush into the flask; it must then be closed, and the flask placed in an
oven at a certain temperature. We have successfully accomplished these
manipulations, thanks to the kind help of our illustrious colleague and
friend, M. Claude Bernard.
The operation is nearly the same in the case of urine. The end of the
free branch of the tap is introduced into the passage of the urethra;
the tap is turned at the moment when the urine is emitted, which is then
allowed to pass into the flask, until it is a third or half filled.
The following were the results of our experiments:—Blood underwent no
putrefactive change even at the highest temperatures of the atmosphere,
but retained the odour of fresh blood, or acquired the smell of lye.
Contrary to what we might have expected, the direct oxidation of the
constituents of blood by slow combustion was rather sluggish. After
subjecting our flasks to a temperature of 25° C. or 30° C. (77° F. to
80° F.) in an oven for several weeks, we observed an absorption of not
more than 2 or 3 per cent. of oxygen, which was replaced by a volume of
carbonic acid gas of about an equal bulk.[29]
Nearly the same results were obtained in the case of urine; it underwent
no radical change; its colour merely assumed a reddish brown tint; it
formed some small deposits of crystals, but without becoming at all
turbid or putrefying in any way. The direct oxidation of the urinary
substances was likewise very sluggish. An analysis of the air in one of
the flasks, made forty days after the commencement of the experiment,
gave the following results:—
Oxygen 19·2
Carbonic acid 0·8
Nitrogen 80·0
——-
100·0
These experiments on blood and urine which we have just mentioned date
from 1863.[30] Ten years afterwards, in 1873, they were confirmed in an
important and striking manner by the results of a very able series of
experiments, which were carried out in our laboratory, by M. Gayon, who
was formerly a pupil in the _École Normale Supérieure_. M. Gayon proved
that what held good in the case of blood and urine, also held good in
the case of the substances contained in eggs. He found that the whites
of eggs might be exposed for any length of time to contact with air, as
also might the yolks, or the white and yolks mixed, without any
putrefactive change or fermentation resulting, and without the smallest
microscopic germ showing itself, the sole condition being that the air
must be freed from all organic particles of dust, germs of mould,
_bacteria_, _vibrios_, and other organisms which it holds in suspension.
This was only a part of the important facts brought to light by M.
Gayon. Amongst other things, he proved that spontaneous putrefaction in
eggs is invariably caused by the development of organized ferments,
thereby correcting the opposite statements announced by M. Donné and M.
Béchamp, who were led by their observations to believe that the change
in eggs took place quite independently of the action of _vibrios_ and
_mucedines_.[31]
It is almost superfluous to remark how greatly the results of these
experiments on blood, urine, and the components of the egg are opposed
to the doctrine of spontaneous generation, as also to most modern
theories on the generation of ferments. As long as experiments relating
to the question of so-called _spontaneous_ generation were made on
heated substances, the advocates of _heterogenesis_ had some grounds for
asserting that such materials could not satisfy the conditions of
spontaneous life, and that we should obtain different results by using
natural organic liquids, which, if exposed to contact of pure air would
doubtless serve for the production of new beings which did not issue
from parents which resembled them. This novel enunciation of the
hypothesis of spontaneous generation, the only one, we think, that could
be defended after the publication of our Memoir, in 1862, is condemned
by the preceding facts.
The same facts completely upset the hypothesis recently maintained by
Messrs. Fremy and Trécul on the subject of the causes of fermentation.
“Side by side with the immediate, definite principles which may be
formed by synthesis,” says M. Fremy, “such as glucose, oxalic acid, and
urea, other substances of greatly inferior stability exist, the
constitution of which is considerably more complicated, containing all
the elements of living organs, such as carbon, hydrogen, oxygen,
nitrogen, and even phosphorus and sulphur; and often salts of lime and
of the alkalies besides. These bodies are albumen, fibrin, casein, the
congeners of vitellin and others. Chemical synthesis cannot reproduce
them. It is impossible, in my opinion, to regard them as immediate,
definite principles. I designate them by the general name of
_semi-organized_ bodies, because they hold an intermediate place between
the immediate principle and the organized tissue.
“These semi-organized bodies, which contain all the elements of organs,
have the power, like a dry seed-grain, of existing in a state of organic
immobility, and of becoming active under circumstances which favour
organic development. By reason of the vital energy that they possess
they undergo a succession of decompositions, giving origin to new
derivatives, and to the advent of ferments, not by any process of
_spontaneous generation_, but by a _vital energy_, which pre-exists in
the semi-organized bodies, and is simply carried on, when this energy
manifests itself, in these most varied organic changes.”
After having expressed these hypothetical and confused opinions, M.
Fremy continues:—“I do not consider, then, that these semi-organized
bodies serve merely as nourishment for certain animal and vegetable
organisms, which may be the sole agents of fermentations, but I give
them a direct _rôle_ and admit that, under the influences which I have
already cited[32] they may assume a real and complete organization, and
produce ferments which are not derived, as we have seen, from a germ or
an ovum but from a semi-organized body, the vital energy of which has
become active.[33] It will be seen that these opinions are quite
different from those which M. Pasteur has maintained in his works, since
they attribute the origin of alcoholic and lactic ferments to an
albuminous substance. Taking the case of alcoholic fermentation alone, I
assert that, in the production of wine, it is the juice of the grape
itself which, in contact with air, produces grains of yeast, by the
transformation of the albuminous substances. M. Pasteur, on the
contrary, maintains that the grains of yeast are produced by certain
germs.”[34]
We have combated these propositions, so extraordinary and unsupported by
any rigorous experiments, before the Academy of Sciences, where they
were first enunciated. On that occasion we related the facts in
connection with blood and urine, which we have just discussed. Could
there be any more forcible argument against the theory of our honourable
colleague than those facts? Here we had natural albuminous substances,
forming part of matter eminently liable to putrefactive change and
fermentation, which produced no ferments of any sort whatsoever when
brought into contact with air deprived of its organic particles of dust.
Under no known circumstances is albuminous matter transformed into
grains of yeast or any other organized ferment, and, to our thinking,
nothing can be more chimerical than the gratuitous hypothesis of
_hemi-organism_.
We shall proceed to new proofs of this, dealing this time with a liquid
formed by the life of a vegetable.
§ III.—Experiments on the Juice contained in Grapes.
In the course of the discussion which took place, at the Academy, on the
subject of the generation of ferments, properly so called, much was said
about the oldest known fermentation, that of wine. We at once resolved
to demolish M. Fremy’s theory, by a decisive experiment on the juice of
grapes.
[Illustration: Fig. 8.]
We prepared forty flasks, capable of holding from 250 c.c. to 300 c.c.
(from 9 to 11 fl. oz.) and shaped as represented in Fig. 8. These we
filled with filtered must, which was perfectly bright, and which, like
all acid liquids, would remain sound, after having been boiled for a few
seconds, although the ends of the long curved necks of the flasks
containing the must might remain constantly open for months or years.
We washed, in a few cubic centimetres of water, part of a bunch of
grapes, washing the grapes separately, or the grapes and the wood
together, or even the wood of the bunch alone. This washing was easily
accomplished by means of a perfectly clean badger’s-hair brush, the
water receiving all the particles of dust adhering to the surface of the
grapes and the wood of the bunch. By means of a microscope we easily
proved that this water held in suspension an infinite number of
organized corpuscles, some of them bearing a very close resemblance to
the spores of fungoid growths, others to alcoholic ferment, others to
_mycoderma vini_, and so on.[35]
[Illustration: Fig. 9.]
We next proceeded to put on one side ten of our forty flasks, to serve
for subsequent corroboration; in ten others, by means of the tube which
is represented on the right hand side of the flask (Fig. 8), we put a
few drops of the water in which the bunch of grapes had been washed; in
a third series of ten flasks we put a few drops of the same liquid,
after having previously boiled it. Lastly, we introduced into the ten
remaining flasks a drop of grape-juice, taken from the inside of an
uninjured grape. To do this we had to bend the right-hand tube of each
of our last ten flasks, drawing it out to a fine point and closing it in
the flame, as represented in Fig. 9 A. This fine closed point was filed
round near its extremity and then thrust, as represented in Fig. 9 B,
into a grape placed on a hard substance; when the point _b_ was felt to
touch the substance supporting the grape it was broken off by a slight
pressure sideways at the point _a_, where the file marks had been made.
We had taken care to secure a slight vacuum in the flask beforehand;
this now caused a drop of the juice to be drawn into the flask. We then
drew out the fine point, and closed it immediately in the flame of a
spirit lamp. The vacuum was produced by heating the flasks in our hands,
or over the flame of a lamp, thus causing a little air to be forced out
through the end of the bent tube, which we then closed up with the lamp.
When the flask was cool, the slight difference of pressure sufficed to
force into it some of the juice contained in the grape, as we have just
described. The drop of juice that is sucked into the flask generally
remains in the curved part of the fine tube; to mix it with the must we
must incline the flask so as to bring the must in contact with the drop;
after that we may replace the flask in its natural position.
The following are the results presented by our four series of
comparative experiments in the different cases. The first ten flasks—our
standard flasks, containing must boiled in contact with pure air—showed
no signs of organized products; the must might have remained in them for
any number of years without change. Our second series of flasks, which
contained the water in which the grapes, separately and in bunch, had
been washed, had undergone alcoholic fermentation in every instance;
this had manifested itself in all the flasks in the course of about
forty-eight hours, the temperature being at about summer heat. At the
same time that the yeast made its appearance in the form of little white
lines, which gradually joining together formed a deposit on the sides of
the flask, we perceived minute flakes of _mycelium_ forming; sometimes
as a single fungoid growth, sometimes combined with another, or with
many together—these growths being quite independent otherwise of the
yeast or alcoholic ferment. In several cases, too, _mycoderma vini_
showed itself on the surface of the liquid in the course of a few days.
_Vibrios_ and lactic ferments, properly so called, could not make their
appearance, on account of the nature of the liquid.
The flasks of our third series, containing the water in which the bunch
of grapes had been washed, and which we boiled before our experiment,
remained as free from change as the flasks of our first series had done.
Lastly, our fourth series of flasks, containing the drops of juice taken
from inside the grapes, remained equally free from change, although we
could not be certain of having removed, in every case, without
exception, all causes of error which must inevitably occur sometimes in
so delicate an experiment.
These experiments cannot leave the least doubt on our minds:
That must, if boiled, will never ferment when in contact with air that
has been freed from the germs which exist in it in a state of
suspension.
That must may be fermented, after boiling, by introducing into it a very
small quantity of water, in which a bunch of grapes has been washed.
That must will not ferment if we introduce into it some of this same
water which has been boiled and afterwards cooled.
That must will not ferment if we introduce into it a small quantity of
the juice contained in a grape.[36]
It follows, then, that the ferment which causes grapes to ferment in the
vintage tub must come from the exterior, and not the interior of the
grapes. Thus, the hypothesis of MM. Trécul and Fremy, according to which
albuminous substances transform themselves into grains of yeast by the
action of a peculiar vital force, is annihilated; _à fortiori_, there
can no longer be a question concerning Liebig’s theory, on the
transformation of albuminous substances into ferments, by a process of
oxidation.
Our readers may be curious to know what M. Fremy has been able to oppose
to such crucial experiments; they could scarcely have imagined the
following:—
“In my experiments, which I have varied in every possible manner,” says
that gentleman, “I have found that it is almost impossible to discover
alcoholic fermentation, appreciable by its results, in a single drop of
grape juice, and I may add that this fermentation must be still more
difficult to discover when this drop has been drowned in a large
quantity of juice that has been previously boiled.”[37]
It will be admitted that we were justified in saying, at the
commencement of this paragraph, that we should demolish the theory which
was opposed to ours, and which its advocates have been constrained to
defend by hypotheses manifestly false.
At the meeting following the one in which M. Fremy declared _that minute
quantities do not ferment_, we had the malicious satisfaction of showing
a great many very small closed flasks, into each of which we had caused
a single drop of the must of crushed grapes to be introduced by suction.
We broke the thin points of many of them, in the presence of the
Academy, and every one of them showed by a sharp hissing, which was
audible at a distance, that fermentation was proceeding in the drop of
liquid they contained. M. Fremy was there, but he made no remark.
We may cite some very curious facts on the subject of the period at
which the germs that develop yeast are in a condition to be able to
cause fermentation.
On July 25th, 1875, in the neighbourhood of Arbois (Jura), the grapes
were still green and of the size of peas. We went to a vine that was far
from paths and roads, and there, with a pair of small scissors, cut some
grapes from off a bunch and let them fall with their short stalks into
tubes half filled with gooseberry must, previously rendered unalterable
by boiling. These tubes we closed again with all possible precautions,
using corks which had been passed through the flame of a spirit-lamp and
carried them to our laboratory, where we left them to themselves. Some
days afterwards we saw diverse fungoid growths appear in most of the
tubes, but not one of them then, or subsequently, presented the least
appearance of fermentation. The germs of yeast at that period of the
year did not exist either upon the woody part of the bunch, or upon the
grapes. In Chapter V. we shall return to observations on this subject.
§ IV.—Wort and Must Exposed to Common Air.
If the principles which we have laid down possess all the value that we
attribute to them, if the cause of change in natural or artificial
organic liquids does not exist in those liquids themselves, if change
considered in itself depends upon the nature and number of the particles
of dust in various places, if it is, besides, radically affected by the
composition of the liquids, it must necessarily follow that wort or
must, whilst, under certain circumstances of exposure to air, it remains
absolutely free from life and its results, will, under other
circumstances, give rise to a variety of organisms and their
corresponding fermentations. This is, in fact, the lesson which direct
proofs will teach us. Before entering upon these new observations in
detail, we must call the reader’s attention to the difficulty, as
experience has shown, of interpreting correctly the facts connected with
the spontaneous impregnations of organic liquids.
Gay-Lussac crushed some grapes under a bell-jar filled with mercury,
after having washed them in hydrogen, to expel the air adhering to the
grapes and the sides of the jar. Having waited for several weeks without
detecting any signs of fermentation, he introduced some bubbles of
oxygen, and fermentation showed itself the following day. Gay-Lussac
concluded that the fermentation of must could not commence without the
help of oxygen.[38]
Under the conditions of his experiment nothing could be truer, and we
must admire the diffidence with which this great natural philosopher
interpreted the fact that he had observed. Another French natural
philosopher, however, M. Cagniard-Latour, observed that the ferment of
alcoholic fermentation was a little cellular plant. What was its origin
in Gay-Lussac’s experiment?
The advocates of the doctrine of spontaneous generation were ready with
their explanation, and we have seen how MM. Trécul and Fremy, following
many others, did not hesitate to maintain that the little plant with all
its particles was produced by the action of oxygen on the albuminous
substances contained in the juice of the grapes. The experiments, which
we have given in the preceding paragraph, show us positively that germs
of the ferment of must exist on the surface of the grape, and that,
consequently, Gay-Lussac’s experiment has a more simple and natural
explanation. The germs of the ferment existing on the surface of the
grape become mixed with the juice of the grape when the latter is
crushed; these germs remain inactive in the presence of hydrogen; they
vegetate as soon as oxygen is introduced to them.
Moreover, the results of our labours in connection with _spontaneous_
generation, in 1862, teach us that in Gay-Lussac’s experiment the germ
of the ferment might also have had its origin either in certain
particles of dust adhering to the sides of the glass bell, or upon the
mercury; and, in a laboratory where alcoholic fermentation is studied,
dust invariably contains dry cells of ferment. The necessity of oxygen
for the success of the experiment is surprising, when we reflect that
alcoholic fermentation often takes place in liquids that are not exposed
to contact with air; but we shall prove by experiment that,
notwithstanding what may happen during fermentation, oxygen has the
greatest influence on the readiness with which ferment develops itself,
and that this gas is indispensable to the revival of withered cells, and
still more so to the germination of special cells, which we may consider
to be the true germs of the little plant.
The advocates of the doctrine of _spontaneous_ generation have based
most of the objections which they vainly urge against their opponents
upon erroneous interpretations of certain facts relating to the
spontaneous impregnation of organic infusions. Taking a very wrong view
of the essential conditions of the phenomena, they require that the
assertors of the diffusion of the germs of microscopic organisms should
be compelled to place at any one point of space, so to say, all the
germs of the products of infusions; a demand which really borders on
absurdity. They believe, or feign to believe, that we are bound to admit
the existence of germs of must in all places and at all times, on the
banks of rivers and on the loftiest mountains, and so on.
“Fermentations,” said one of these gentlemen one day, before the
Academy, “cannot depend upon chance particles of atmospheric dust. How
is it possible that germs of yeast can be present everywhere throughout
the universe, ever ready to fall upon must?” It is an established fact
that grapes crushed in any part of the globe whatsoever, even on a
glacier or at the highest elevations, can set up a fermentation. The
explanation of this pretended impossibility is most simple, for we know,
from the facts related in the preceding paragraph, that grapes carry on
their skins the germs of their own ferments.
In experiments relating to the kind of organisms which we are discussing
we must never fail to take into account the action of the particles of
dust spread over the articles that are used. Very often an effect that
should be attributed to germs adhering to the vessels and utensils used
in experiments, the origin of which may be altogether special, is
erroneously imputed to the dust-forming germs—that is to say, to those
germs which exist in a state of suspension in the air.
In our Memoir of 1862, which we have quoted several times, we have
explained that it is almost impossible to draw any serious conclusions
from experiments made in a basin of mercury, because of the organic
particles of dust which always exist in that metal, and which, without
the knowledge of the operator, pass into the interior of the vessel,
where they produce certain changes which one is tempted to impute to
_heterogenesis_.
In all classical works an experiment of Appert’s, reproduced by
Gay-Lussac, is given. This, through a faulty interpretation, led to the
hypothesis of the continuity of the causes of fermentation, if we may
use such a term, in the atmospheric air.[39]
When we decant bottles of must, which has been preserved by Appert’s
method, into other bottles, all the latter soon set up a fermentation:
this constitutes the experiment. If it were proved that the must, whilst
being decanted, came in contact with atmospheric air alone, as
Gay-Lussac believed, we should be compelled to admit, according to the
theory of germs, that the must had come in contact with some particles
of ferment in the air during decanting. And again, if it were shown that
the experiment could succeed in any place whatsoever, we must come to
the conclusion that germs of ferment exist everywhere in a state of
suspension in the air.
“I have taken,” writes Gay-Lussac, “a bottle of must that had been
preserved for a year and was perfectly transparent, and have decanted
the must into another bottle, which I then carefully corked and exposed
to a temperature of 15° C. to 30° C. (59° F. to 86° F.). Eight days
afterwards the must has lost its transparency; fermentation has taken
place in it, and soon my must has become transformed into a vinous
liquor, sparkling like the best champagne. A second bottle of must that
had been preserved for a year, like the preceding one, but which had not
been brought into contact with the air, has presented no signs of
fermentation, although placed under conditions most favourable to its
development.”
The result of this experiment, when roughly made, is correctly described
by Gay-Lussac; in other words, it may be proved that if, at the time of
vintage, we prepare some bottles of must, after Appert’s process, and,
in the course of time, open them and decant their contents into other
bottles, we shall soon see the must ferment and deposit yeast. It is,
nevertheless, equally certain that the inferences which have been drawn
from this celebrated experiment have been founded on error, and that the
germs of yeast are very rarely derived from the particles of dust
floating in the air with which the must comes in contact. The germs in
question are, in our opinion, generally derived, not from the air, but
from the sides of the bottles, from corks, from the string employed in
corking, from corkscrews, and from a variety of other things. The reason
for this is that any room, vault, cellar, or laboratory where the
grapes, or must, or vintage, are handled—unless special precautions, of
which Appert and Gay-Lussac certainly never thought, are taken—all the
utensils, as well as all articles of clothing, and all the sides of the
bottles which the hands have touched, are contaminated by cells of
ferment derived from must that has fermented, or by germs from the
surface of grapes and clusters. Thus, at the moment of decanting the
must, a thousand accidental circumstances may lead to the introduction
of those germs, the origin of which, as we have seen, may be actually
traced to the very grapes which served for the manufacture of the must.
In other words, we believe the inference that the germs of yeast which
cause the experiment to succeed, are derived from particles of dust
floating in the air of the place where we decant the contents of our
bottles, to be altogether an erroneous one.
Since the preceding remarks were written, we have endeavoured to repeat
this experiment of Gay-Lussac’s in such a manner as we believed would
confirm our views, by varying the conditions in such a way as would
cause it to succeed or fail, according to the circumstances of the
manipulation employed.
On December 7th, 1874, we took two bottles of must which we had
preserved, after Appert’s process, in our laboratory from the beginning
of October, 1873. Both of these were covered with dust—the dust that
floated about in our laboratory. We decanted them as follows:—One
bottle, which we handled without special precautions, we uncorked by
means of an ordinary corkscrew, and decanted into another bottle that
had been well washed, as bottles are washed when they are to be used
subsequently. This bottle was taken from a number that had been standing
upside down on a drainer for a fortnight. We took no precaution to
remove the dust which covered the exterior of the bottle of must, or to
purify the washed bottle. The second bottle of must, on the other hand,
was decanted after we had removed the dust that covered it; its cork was
cut off close to the string, and the flame of a spirit lamp was passed
over the string and the surface of the cork; and, as a final precaution,
the corkscrew was passed through the flame. As for the bottle into which
we subsequently decanted the must, we first plunged it in a hot-water
bath kept at 100° C. (212° F.), then took it into a garden to cool
upside down in the open air. After these precautions we removed it, and
immediately decanted into it the must from the second bottle.
The first bottle showed signs of growths, both on the surface and at the
bottom of the must, the day after the operation, and manifested the
first symptoms of alcoholic fermentation on December 16th. The contents
of the second bottle remained perfectly unchanged after being exposed to
the warmth of a stove for several months.
Can anything be more conclusive than these facts? They are in perfect
keeping with the views that we have recently expressed, and with the
principles that we have maintained for nearly twenty years, on the
subject of the causes of change in organic liquids.