FERMENTED MILKS
There is considerable variety in the number of soured or fermented
milks, and they are known by various names, such as Koumiss or Koomiss,
which is prepared from mares' milk; Keffir, which was originally
discovered in the mountains of the Caucasus, and which is prepared with
Keffir grains; Leben, an Egyptian product prepared from the milk of the
buffalo, cow, or goat; Matzoon, a soured milk which is prepared in
Armenia from ordinary cows' milk; Dadhi, an Indian preparation from
cows' milk. All of these owe their special characteristics to the fact
of their having undergone lactic and alcoholic fermentation.
"Milk left to itself," says Blyth,[14] "at all temperatures above 90° F.
begins to evolve carbon dioxide, and this is simply a sign and result of
fermentation. If this fermentation is arrested or prevented, the fluid
remains perfectly sweet and good for an indefinite time. Besides the
production of carbon dioxide during decomposition, a certain portion of
milk sugar is converted into lactic acid, some of the casein and albumen
are broken up into simpler constituents, and a small proportion of
alcohol produced, which by oxidation appears as acetic acid, while the
fat is in part separated into free fatty acids, which ultimately unite
with the ammonia produced by the breaking up of the albuminoids. The
main fermentation of milk is a special kind which of late years has been
much studied, and is known as _lactic fermentation_. Accompanying lactic
fermentation there is nearly always a weak butyric and a weak alcoholic
fermentation."
One of the organisms causing _Butyric Acid Fermentation_ is a bacillus 3
to 10µ in length, and about 1µ in breadth. It has power of movement, and
when cultivated in gelatine, liquefies the gelatine, forming a scum on
the surface. When the bacillus is sown into sterile milk, the following,
according to Hueppe, are the changes:
"If the milk thus infected is incubated, on the second day a clear,
slightly yellow fluid is seen under the layer of cream; this fluid
increases from day to day, so that gradually a column of fluid is
formed which is quite clear above, but below is turbid; the casein, at
first thrown down in a firm coagulum, in the course of eight days begins
to be attacked, and by the end of two or three weeks most of it is
dissolved. The filtered fluid gives the biuret reaction; it contains
leucin, tyrosin, and ammonia; hence it is clear that the ferment acts to
some extent as a digestive of albumen. In advanced butyric acid
fermentation, the fluid is most offensive, and may have an alkaline
reaction."
Lactic acid was first isolated by Scheele in 1780 from soured milk, but
its exact constitution was not determined until later by Liebig,
Mitscherlich, Gay-Lussac, and Pelouze: "It is widely distributed in
nature, occurring in the sap of the vine and in most fermented liquids,
especially in soured milk; it is not, however, present in fresh
milk."[15]
In all the Eastern preparations referred to, the lactic fermentation is
produced, followed by alcoholic fermentation, which is due to the slow
decomposition of the milk sugar, the vinous fermentation being most
readily set up in milks which contain a larger relative proportion of
milk sugar and water, such as the milk derived from the mare, the sheep,
and the camel. As these fermented milks have different characteristics,
it is necessary to the thorough understanding of the process of
manufacture at the present day, to examine them in some detail.
_Koumiss._--The greatest of all the fermented milks is koumiss, and it
has been celebrated from the most ancient times until the present day,
as being the principal food of the wandering tribes of Khirgiz,
Bashkirs, Kalmucks, and Tartars, who inhabit the steppes of European
Russia and the plains of South, Western, and Central Asia. According to
Carrick, who has written an interesting volume on the subject,[16] the
nomads who inhabit these vast territories are shut up under the most
miserable circumstances during the winter time and at the advent of
spring they roam over the steppes from morning to night, usually in the
saddle. The milk yielded at such time by the mares is carefully
collected, and these nomads consume enormous quantities of it in the
fermented state, this habit having been in existence amongst them from
time immemorial. It is said that the Scythians, long before the
Christian era, used fermented mares' milk; and there are ornaments in
existence in Russia, of Scythian origin, which exhibit in detail the
preparation of koumiss from mares' milk. In historical times, the first
mention of koumiss was in the twelfth century, when it is referred to in
the Ipatof Chronicles. During the thirteenth century William de
Rubruquis, a French missionary, wrote about his travels in Tartary, and
he described how he had first become acquainted with koumiss, and how he
found it savoury to the palate. Subsequent to this, however, there is
very little mention of koumiss in Russian history, or, for that matter,
in any other, and the first really scientific contribution on the
subject was by Dr. John Grieve, who was a surgeon in the Russian army,
and who in the year 1784 sent a description of koumiss to the Royal
Society of Edinburgh,[17] of which he was a member, and the title of it
was, "An Account of the Method of Making Wine called by the Tartars
Koumiss, with Observations on its Use as a Medicine." Dr. Grieve
strongly advocated the use of koumiss as beneficial in cases of wasting
diseases, and subsequently it was adopted by the medical profession,
with the result that sanatoria for the treatment of pulmonary
consumption were established at Samara and other places in Russia, and
met with very great success; and at the present day such sanatoria are
carried on, but the bacteriology of the subject now being thoroughly
understood, the methods of preparation have been somewhat modified.
An interesting account of koumiss is given by Clarke,[18] who says:
"Everybody has heard of koumiss, and the brandy which the Kalmucks are
said to distil from the milk of mares. The manner of preparing these
liquids has been differently related, and perhaps is not always the
same. They assured us that the brandy was merely distilled from
buttermilk. The milk which they collect overnight is churned in the
morning into butter; and the buttermilk is distilled over a fire made
with the dung of their cattle, particularly the dromedary, which makes a
steady and clear fire like peat. But other accounts have been given both
of the koumiss and the brandy. It has been usual to confound them, and
to consider the koumiss as their appellation for the brandy so obtained.
By other information I could gain, not only here, but in many other
camps which we afterwards visited, they are different modifications of
the same thing although different liquors; the koumiss being a kind of
sour milk, like that so much used by the Laplanders called _pina_, and
which has undergone, in a certain degree, the vinous fermentation; and
the brandy an ardent spirit obtained from koumiss by distillation. In
making koumiss they sometimes employ the milk of cows, but never if
mares' milk can be had, as the koumiss from the latter yields three
times as much brandy as that made from cows' milk.
"The manner of preparing the koumiss is, by combining one sixth part of
warm water with any given quantity of warm mares' milk. To these they
add, as a leaven, a little old koumiss, and agitate the mass till
fermentation ensues. To produce the vinous fermentation, artificial heat
and more agitation is sometimes necessary. This affords what is called
koumiss. The subsequent process of distillation afterwards obtains an
ardent spirit from the koumiss. They call it _vina_. In their own
language it bears the very remarkable appellation of _rack_ and _racky_,
doubtless nearly allied to the names of our East India spirit _rack_
and _arrack_. We brought away a quart bottle of it, and considered it
very weak bad brandy, not unlike the common spirit distilled by the
Swedes and other northern nations. Some of their women were busy making
it in an adjoining tent. The simplicity of the operation and their
machinery was very characteristic of the antiquity of this chemical
process. Their still was constructed of mud, or very coarse clay; and
for the neck of the retort they employed a cane. The receiver of the
still was entirely covered by a coating of wet clay. The brandy had
already passed over. The woman who had the management of the distillery,
wishing to give us a taste of the spirit, thrust a stick, with a small
tuft of camel's hair at its end, through the external covering of clay,
and thus collecting a small quantity of the brandy, she drew out the
stick, dropped a portion on the retort, and, waving the instrument above
her head, scattered the remaining liquor in the air. I asked the meaning
of this ceremony, and was answered that it is a religious custom to give
always the first drop of the brandy which they draw from the receiver to
their God. The stick having been plunged into the receiver again, she
squeezed it into the palm of her dirty and greasy hand, and after
tasting the liquor, presented it to our lips."
Another interesting account of the preparation of koumiss is given by
John M. Wilson in the _Rural Encyclopædia_,[19] and it shows that the
methods in use about the middle of last century did not differ
materially from those which existed centuries before.
Wilson says: "Khoumese is vinously fermented mares' milk. Any quantity
of fresh mares' milk is put into wooden vessels; a sixth part of water
just off the boil is mixed with it; an eighth part of old khoumese or of
the sourest possible cows' milk is added; the mixture is kept from
fifteen to twenty-four hours, covered up with several folds of coarse
linen cloth and with a very thick board, and without being stirred or in
any degree disturbed, in a moderately warm place till it becomes
thoroughly sour, and sends up a thick mass to its surface; it is then
beaten and pounded and stirred till the curd is not only broken, but so
thoroughly mixed with the serum as to form a thick liquid; it next
remains covered and at rest during twenty-four hours more, and it is
finally put into a common butter churn and beaten and blended into a
state of perfect homogeneity. It is now fit for use; yet it acquires an
increase of given properties if it be allowed to stand for a few days,
and either then or now it would, if distilled, yield nearly one third of
its own bulk of a weak spirit which will bear to be rectified. Whenever
it is used it must be previously so agitated that its component parts
may be well mixed together, and it may be kept either in pans for
immediate use or in casks for more remote use; and if placed in a cool
cellar it will remain good during three or four months."
Mares' milk owes its peculiar fitness for making koumiss to its
containing a large proportion of sugar of milk, and readily undergoing
the vinous fermentation, and it possesses a general medicinal reputation
among the Tartars similar to that which asses' milk has partially
acquired in Britain. "That mares' milk will undergo vinous fermentation
and yield a certain quantity of spirit," says a writer in the _Magazine
of Domestic Economy_, "is not generally known, and it was reserved for a
nation of demi-savages to render this circumstance available as an agent
of health, as well as an agreeable and nourishing beverage. Every
educated person, however, has heard that the Tartars drink mares' milk,
though few know that this milk is taken on account of its specific
virtues alone, and not as a substitute for cows' milk, of which they
have abundance, and with which they adulterate mares' milk when scarce."
But the koumiss is reputed to be much more medicinal than the mares'
milk itself; and on account of its being free from all tendency to
curdle in the stomach, and of its possessing most of the nutritive power
of the milk in combination with native fermented spirit, it has been
strongly recommended by some persons as a remedy for most or all cases
of general debility, of nervous languor, and even pulmonary disease.
"Khoumese is called sometimes _koumiss_ and sometimes milk wine."
From these references it will be seen that koumiss is an alcoholic drink
made by the fermentation of mares' milk, but it is also frequently
prepared from the milk of the camel and cows' milk. It is stated that a
similar preparation to Russian koumiss is made in Switzerland from cows'
milk simply by the addition of a little sugar and yeast to skim milk;
"it contains more sugar and less lactic acid than Russian koumiss, and
on account of the much greater proportion of casein contained in cows'
milk, differs considerably from that prepared from mares' milk."
Suter-Naef gives the composition of a Swiss koumiss[20] manufactured at
Davos as follows:
In Grams. Per Litre
Per cent. (by weight).
Water 90.346 1019.64 grams.
Alcohol 3.210 36.23 "
Lactic acid 0.190 2.14 "
Sugar 2.105 23.75 "
Albuminates 1.860 20.99 "
Butter 1.780 20.09 "
Inorganic salts 0.509 5.74 "
Free carbonic acid 0.177 2.00 "
The ferments used in the preparation of koumiss are stated by Carrick to
be of two different kinds, artificial and natural.
"Of the natural ferments two have been resorted to. One is mentioned by
Grieve, which he borrowed from the Bashkirs of Orenbourg, and which
simply consists in the addition of one sixth part of water and one
eighth of the sourest cows' milk to fresh mares' milk; the other has
been employed, and was, if I mistake not, first recommended by
Bogoyavlensky. It is a very simple if rather a tedious method. New
mares' milk, diluted with one third its bulk of water, is placed in the
_saba_,[21] and while allowed to sour spontaneously, is continually
beaten up. This milk gradually undergoes the vinous fermentation, and in
twenty-four hours is converted into weak koumiss. The disadvantage of
this mode of commencing fermentation is obvious--viz., the great waste
of time in agitation. Hence it is only employed when no artificial
ferment is obtainable.
"In starting the process of fermentation in mares' or any other kind of
milk, therefore, an artificial ferment is more frequently employed than
a natural one. The former is used only for converting the first portion
of milk into koumiss; the latter is always resorted to afterwards.
"Of artificial ferments the variety is great, for besides all putrefying
animal matters which contain nitrogen--such as blood, white of egg,
glue, and flesh--certain mineral substances which act by souring the
milk are also capable of exciting fermentation.
"Now, many of the nomads, whose mares either give no milk or are not
milked in winter, commence the preparation of their koumiss in spring by
borrowing a ferment from the animal, mineral, or vegetable kingdom. Thus
a mixture of honey and flour is the favourite ferment with some races of
nomads; a piece of fresh horse-skin or tendon is preferred by others,
while a few resort to old copper coins, covered with verdigris, for
starting fermentation. In the choice of a ferment they are guided solely
by habit and tradition. As it would be useless, almost impossible, to
give a list of all the foreign substances that have been employed with
the view of converting mares' milk into koumiss, it will be best to
consider the simplest artificial ferments, and those most generally in
use.
"The simplest way is that recommended by Bogoyavlensky, and adopted and
modified by Tchembulatof.[22] It is prepared thus: 'Take a quarter of a
pound of millet-flour, add water to it, and boil it down to the
consistence of thick oatmeal porridge. Then heat separately, in another
vessel, eleven pints of milk to boiling-point, and allow it to cool
down. When its temperature has fallen to 95° F., pour it into a wooden
bowl or tub, and add the boiled flour to it. The upper and open part of
the vessel is then covered with a piece of coarse linen, and left at
rest--at a temperature of about 99° F.--from twenty-four to forty-eight
hours. The appearance of small bubbles, which keep bursting on the
surface of this liquid, combined with a vinous or acid odour, prove that
the ferment is ready. To this fermenting fluid twenty-two quarts of new
milk are gradually (_i.e._, every ten minutes) added, and the whole mass
is continuously beaten up for twelve hours. The temperature during
stirring should never be higher than 94° F. The whole fluid soon begins
to ferment, and after twelve hours a not unpleasant koumiss is ready.
This should be filtered through a horse-hair or muslin sieve, after
which it is fit for drinking. This liquid is called weak koumiss; but a
limited portion of the lactine has undergone the lactuous and vinous
fermentations, and thus the percentage of alcohol is small. Koumiss at
an ordinary temperature remains weak for twelve hours after it has been
beaten up, and then gradually passes into medium.'"
Curiously enough, the richness of cows' milk in fat militates against
its being a good raw material for the making of koumiss, owing to the
production of small quantities of butyric acid, which follows upon the
fermentation, so that it is desirable, if koumiss is to be prepared from
cows' milk, that the fat should be first of all eliminated, so that the
separated milk will then approximate to the composition of mares' milk.
"The chemical changes," says Hutchison,[23] "which take place in the
milk under the double fermentation are not difficult to follow; the
lactic ferment simply changes part of the sugar into lactic acid, the
vinous ferment eats up a very small part of the proteid of the milk,
and, at the same time, produces from the sugar a little alcohol and a
good deal of carbon dioxide; the milk thus becomes sour, it effervesces
and is weakly alcoholic, but the lactic acid causes the casein to be
precipitated just as it does in the ordinary souring of milk, and the
casein falls down in flocculi."
As will have been noticed, it is an essential part of the process of
koumiss-making to keep the milk in a state of agitation during the
period of fermentation, a process which is intended to permit of oxygen
being taken up by the fermenting fluid, while, at the same time, the
casein is broken up into a state of fine division. The casein also, or
at least a portion of it, becomes very soluble, and after twelve hours
of fermentation the taste of the product is only slightly sour, and the
milk taste still remains. This taste, however, disappears in
twenty-four hours, owing to the rapid development of the lactic acid
organisms. After this lapse of time the sugar is entirely destroyed, and
the strong koumiss which results is a thin sour fluid which effervesces
briskly, and in this condition will keep for an indefinite period. "The
net change which has taken place in the original milk may be summed up
by saying that the sugar of the milk has been replaced by lactic acid,
alcohol, and carbon dioxide, the casein has been partly precipitated in
a state of very fine division, and partly pre-digested and dissolved,
while the fat and salts have been left much as they were."[24]
Violent stirring or agitation of the cultures does not seem to work so
much by supplying oxygen to the fermenting liquid, as by ensuring a
thorough distribution of the micro-organisms throughout the liquid, and
thus dividing the casein.
The greater number of the organisms are facultative anærobes and oxygen
is not necessary. Again, koumiss put up in bottles on the first day is
regularly shaken although air is excluded.
_Keffir._--Keffir is a kind of fermented milk which has been in use in
the Caucasus for quite a long time, as koumiss has been in the steppes.
It differs from koumiss, however, in this respect, that it is prepared
from either sheep's, goats', or cows' milk. The process is started by
the addition of keffir grains to the milk, which is contained in
leathern bottles. These keffir grains are small solid kernels which are
kept in families and handed on from one generation to another.[25] The
grains are the origin of the ferment, as they disseminate in the milk
micro-organisms of a lactic yeast (_Saccharomyces kefir_ Beyerinck and
Freudenreich) and also the bacillus _Bacterium caucasicum_, which
develop rapidly and split up the milk sugar into carbon dioxide,
alcohol, and lactic acid. Small quantities of glycerine, acetic,
succinic, and butyric acids are also formed, the casein and albumen
being partly peptonised.[26] Keffir becomes slightly effervescent in
twenty-four hours, and in that time develops a small quantity of
alcohol, but after three days the amount of alcohol and lactic acid
is much increased.[27] It has been determined that the fermentation of
the milk is due to _Saccharomyces kefir_, and that the _Lactobacillus
Caucasicus_ does not take any part in the fermentation, a fact which
seems to be supported by the capacity of ordinary keffir for starting
the fermentation in fresh milk in the same manner as the keffir grains.
The use of this beverage seems to be universal throughout the Caucasus,
and travellers in these regions have frequently referred to it. Thus
Freshfield[28] states in one part of his book of travels as follows:
"The pig-faced peasant against whom we had at first sight conceived such
an unjust prejudice turned out a capital fellow. He brought us not only
fresh milk, but a peculiar species of liquor, something between
public-house beer and sour cider, for which we expressed the greatest
admiration, taking care at the same time privately to empty out the
vessel containing it, on the first opportunity." And again:
"The hospitable shepherds regaled us, not only with the inevitable and
universal airam or sour milk--if a man cannot reconcile himself to sour
milk, he is not fit for the Caucasus--but with a local delicacy that
has lately been brought to the knowledge of Europe--kefir. This may best
be described as 'effervescing milk.' It is obtained by putting into the
liquid some yellow grains, parts of a mushroom which contains a bacillus
known to science as _Dispora caucasia_. The action of the grains is to
decompose the sugar in the milk, and to produce carbonic acid and
alcohol. The grains multiply indefinitely in the milk; when dried they
can be preserved and kept for future use; its results on the digestion
are frequently unsatisfactory, as one of my companions learnt to his
cost."
"It has been supposed," says Metchnikoff, "that the chief merit of
kephir was that it was more easy to digest than milk, as some of its
casein is dissolved in the process of fermentation. Kephir, in fact, was
supposed to be partly digested milk. This view has not been confirmed.
Professor Hayem thinks that the good effects of kephir are due to the
presence of alcoholic acid, which replaces the acid of the stomach and
has an antiseptic effect. The experiments of M. Rovigh, which I speak of
in _The Nature of Man_, have confirmed the latter fact, which now may be
taken as certain. The action of kephir in preventing intestinal
putrefaction depends on the lactic acid bacillus which it contains.
Kephir, although in some cases certainly beneficial, cannot be
recommended for the prolonged use necessary, if intestinal putrefaction
is to be overcome.... Professor Hayem prohibits its use in the case of
persons in whom food is retained for long in the stomach. When it is
retained in the stomach, kephir goes on fermenting, and there are
developed in the contents butyric and acetic acids, which aggravate the
digestive disturbances. Kephir is produced by combined lactic and
alcoholic fermentations ... and it is the lactic and not the alcoholic
fermentation on which the valuable properties of kephir depend; it is
correct to replace it by sour milk, that contains either no alcohol or
merely the smallest traces of it. The fact that so many races make sour
milk and use it copiously is an excellent testimony of its usefulness."
There are two methods given by Flügge[29] for the preparation of keffir:
"In the first, the dry brown kefir grains of commerce are allowed to lie
in water for five or six hours until they swell; they are then carefully
washed and placed in fresh milk, which should be changed once or twice
a day until the grains become pure white in colour and when placed in
fresh milk, quickly mount to the surface--twenty to thirty minutes. One
litre of milk is then poured into a flask, and a full tablespoonful of
the prepared _körner_ added to it. This is allowed to stand open for
five to eight hours; the flask is then closed and kept at 18° C. It
should be shaken every two hours. At the end of twenty-four hours the
milk is poured through a fine sieve into another flask, which must not
be more than four fifths full. This is corked and allowed to stand,
being shaken from time to time. At the end of twenty-four hours a drink
is obtained which contains but little carbon-dioxide or alcohol. Usually
it is not drunk until the second day, when, upon standing, two layers
are formed, the lower milky, translucent; and the upper containing fine
flakes of casein. When shaken it has a cream-like consistence. On the
third day it again becomes thin and very acid. The second method is used
when one has a good kefir and two or three days to start with. Three or
four parts of fresh cows' milk are added to one part of this and poured
into flasks which are allowed to stand for forty-eight hours with
occasional shaking. When the drink is ready for use, a portion (one
fifth to one third) is left in the flask as ferment for a fresh quantity
of milk. The temperature should be maintained at about 18° C., but at
the commencement a higher temperature is desirable. The grains should be
carefully cleaned from time to time and broken up to the size of peas.
The clean grains may be dried upon blotting-paper, in the sun, or in the
vicinity of a stove; when dried in the air they retain their power to
germinate for a long time."
_Leben._--In our earlier references to fermented milks in scriptural
times, we observed that alcoholic fermented milks were not permitted to
be presented at the altar. Such offerings, however, were quite allowable
amongst the ancient Egyptians, the Arabs and Carthaginians,[30] and from
remote antiquity these nations placed great value on this product.
Leben, which is peculiarly associated with Egypt, is a soured milk
prepared from the milk of buffaloes, cows, or goats. It is usually
prepared by the boiling of the fresh milk over a slow fire, after which
some fermented milk from a previous preparation is added to the warm
article, and the fermentation takes place rapidly and is considered to
be complete in about six hours.[31] The Egyptian leben is valued so
highly that it is offered in hospitality to the passing stranger, and it
is regarded as so much of a duty to present this milk, that in some
parts of Arabia it would be looked upon as scandalous if any payment
were received in return.[32]
_Matzoon._--Matzoon is prepared in Armenia in somewhat the same manner
as keffir is prepared in the Caucasus, and indeed it differs very
slightly from keffir in composition. Its use is universal in Armenia.
_Dadhi._--In India large quantities of fermented milk are used, under
the name of Dadhi, and its characteristics are not unlike the similar
products in Europe. The specific bacillus has been investigated by
Chatterjee,[33] who concludes that it is somewhat akin to the _Bacillus
bulgaricus_ and the bacillus of leben (_B. lebenis_). Dr. Chatterjee
gives a résumé of his investigations which sums up the whole matter
thus:
"1. The fermented milk of India called Dadhi resembles in all essential
points the Bulgarian fermented milk as well as the leben and other forms
of fermented milk in use in the East.
"2. The causative element of the curdling process of Dadhi is a
streptothrix having characters similar to the _Bacillus bulgaricus_ and
_Streptobacilli lebeni_, and _Bacillus caucasina_ and the Long Bacilli
of Mazun, in (1) not growing in ordinary media; (2) producing a large
amount of lactic acid in milk; (3) producing, besides coagulation of
casein and splitting up the sugar of milk into lactic acid, no other
change in milk; (4) not producing any indol, nor peptone, nor
saponification of fat, nor formation of any gas.
"3. It differs from the above by showing peculiar pink-stained granules,
when stained with methylene blue and showing peculiarly convoluted
chains in glucose agar.
"4. The importance of the organism lies in the fact that, as in the case
of _Bacillus bulgaricus_, it kills all pathogenic non-sporing germs and
also destroys all proteolytic gas-forming bacilli in milk."
In the account of these investigations the following table is given,
showing the amount of lactic acid produced by different lactic acid
bacilli in one litre of milk, in terms of lactic acid--the culture
being kept at 37° C.
+--------------+-------+-------+-------+-------+-------+-------------------+
| Name of the | After | After | After | After | After | |
| Bacillus. | 24 | 48 | 72 | 96 | a | Remarks |
| | Hours.| Hours.| Hours.| Hours.| Week. | |
+--------------+-------+-------+-------+-------+-------+-------------------+
| B. lactis | 1.8 | ... | 10.08 | ... | ... | Observed by |
| ærogenes | | | | | | Hall and Smith |
| | | | | | | |
| B. coli | 1.8 | ... | 4.77 | ... | ... | Observed by |
| communis | | | | | | Hall and Smith |
| | | | | | | |
| B. | 12.8 | 16.5 | 20.2 | ... | 22 | Observed by |
| bulgaricus | -.4 | -.4 | -.4 | ... | -.4 | Gabriel Bertrand |
| | | | | | | and Weisweller; |
| | | | | | | the initial |
| | | | | | | acidity of the |
| | | | | | | milk was 4 |
| | | | | | | |
| Matzoon Long | 10.8 | 12. | ... | ... | ... | Observed by |
| stäbschen B.| | | | | | Düggeli |
| | | | | | | |
| Strepto- |2.61[34] ... | ... | ... | ... | Observed by |
| bacillus | | | | | | Rist and Khoury |
| lebenis | | | | | | |
| | | | | | | |
| Streptothrix | 10.8 | 1.08 | 11.25 | 11.70 | 18.5 | Med. Coll., |
| dadhi | | | | | | Calcutta |
+--------------+-------+-------+-------+-------+-------+-------------------+
In different parts of the world sour milk is consumed in great
quantities, and it is stated by Metchnikoff[35] that the chief food of
the natives of tropical Africa consists of soured milk, and in Western
Africa in the region south of Angola, the natives live almost entirely
on this product, there being a difference in the curdled milks produced
according to the nature of the microbial flora which is introduced.
It is stated[36] that in Servia, Bulgaria,[37] and Roumania there were
5000 centenarians living in 1896, and while many reasons are advanced
for such an abnormal condition of affairs, it seems fairly certain that
the sole reason why people in these districts live to such great ages is
because of their mode of living and the fact that they live very largely
on soured milk. The hygienic conditions throughout these countries are
not such as would give the population in the towns and villages any
special advantages in the prolongation of life, and while it may be
stated that a pastoral and agricultural life are likely to contribute to
longevity, these conditions would not account for a general tendency to
live long in the countries referred to, more than in any other
agricultural area. There are many countries throughout the world in
which the pastoral and agricultural existence is general, but it has
not been shown that in these countries life is prolonged. Hence the
conclusion has been forced upon investigators that the reason is to be
found not in the pastoral conditions, but in the habit which has existed
from time immemorial of consuming sour milk as a principal article of
diet.
There is no curtailment of the use of fermented milks in Eastern Europe,
and the methods of preparation at the present day are those which have
been carried out from time immemorial. A local observer states that in
Bulgaria yoghourt is made in nearly every household, especially in the
spring and summer. The method of preparation is very simple: The milk is
boiled until a quarter of its volume has evaporated, it is then cooled
to 45° C. and the ferment added. This ferment is a portion of the
yoghourt of good flavour and is called "Maya" or "Zakvaska." The vases,
a kind of earthenware pot, are enveloped in woollen stuff or sheepskin
and placed in a warm place near the chimney. In ten hours the yoghourt
is made, and it is preserved in a cold place. The great reputation that
the yoghourt has acquired in Western Europe has caused this "Maya" to
become an article of commerce. It is sent out by rail hermetically
sealed in tinplate boxes. According to a Sophia chemist, the "Maya" is
employed in the following manner: For a litre of milk it is necessary to
take about 10 gr. of the ferment. This ferment is diluted with three
times the amount of water and put into a bowl previously heated with hot
water and dried. Into this bowl the milk, previously boiled and cooled
to a temperature of 75° to 50° C., is poured; it is then covered over
and put in a temperature of about 30° C., and, in default of a stove of
constant temperature, the bowl is wrapped round with flannel or a plaid,
and left to curdle for eight to ten hours. It is then ready for
consumption. During winter, curdled milk keeps for several days, and in
summer it becomes sour in from twelve to twenty-four hours.
A similar food to the yoghourt is prepared in the Balkan mountains from
sheep's milk under the name of "Urgoutnik."[38] The milk is poured into
a goat-skin or sheepskin bag, and a little of the fermented milk added,
and is then left for some hours in a warm place. The milk consumed is
replaced by a fresh supply. In some of the Balkan countries, they are
not content with the fermentation of the milk, they add a little alum,
which, under the name of "typsa," is well known for this purpose. The
milk attains such a solid consistency that it can be put into a cloth
and carried to market.[39]
The various forms of sour milk which have been described in the
foregoing pages may be said to be of the traditional kind, and with the
light of modern knowledge, it has been possible to determine exactly
what constitutes the active principle in use in the milk consumed in
these countries, and, as we shall see, this principle has been applied
so that, at the present day, a pure fermented milk may be obtained in
any country, and there is every reason to believe that should such be
adopted as a general article of food, it would contribute to the
prolongation of human existence.
It is due to Metchnikoff, of the Pasteur Institute, that so much
prominence has been given to the use of fermented milks. He gave it as
his opinion[40] that senility was caused partly by auto-intoxication or
by the poison derived from putrefactive micro-organisms which inhabit
the digestive track. These organisms increase with age, and under
certain unhealthy conditions multiply enormously, particularly in the
large intestine. Having arrived at this knowledge, Metchnikoff set to
work to devise some means of combating the influence of these harmful
microbes, and set up the hypothesis that the tendency to longevity which
is exhibited in Eastern countries is due to the consumption of lactic
acid organisms in the shape of soured milk. These organisms are more
powerful than those of a putrefactive character and inhibit their
growth.
"In the presence of such facts," says Metchnikoff, "it becomes
exceedingly important to find some means of combating the intestinal
putrefaction which constitutes so incontestable a source of danger. Such
putrefaction is not only capable of producing diseases of the digestive
tube--_enteritis_ and _colitis_--but even of becoming a source of
intoxication of the organism in its most varied manifestations.
"It is some years since I proposed to combat intestinal putrefaction and
its injurious consequences by means of lactic ferments. I thought the
acidity produced by such microbes would be much more effective in
preventing the germination of putrefying microbes than the small
quantity of acids produced by _Bacillus coli_. On the other hand, I had
no illusion as to the difficulty sure to be encountered in any effort to
introduce lactic microbes into the intestinal flora which has been
preoccupied by a multitude of other microbes. To make surer of the
result, I chose the lactic microbe, which is the strongest as an acid
producer. It is found in the _yahourt_ (yoghourt), which originates in
Bulgaria. The same bacillus has also been isolated from the _leben_ of
Egypt; and it is now proved that it is found in the curdled milk of the
whole Balkan peninsula, and even in the Don region of Russia."[41]
It is a short step from considerations like these to the adoption of the
_Bacillus bulgaricus_ as the most potent of the various lactic organisms
which have been examined, and which is likely to play such an important
rôle in the destiny of the human race. The _Bacillus bulgaricus_ may
claim to be the Bacillus of Long Life.