THE PREPARATION OF SOURED MILK IN THE HOUSE
There is no great difficulty in making soured milk at home: the
necessary operations are quite simple, but at the same time they must be
conducted with precision and care, otherwise the results may be
unsatisfactory and disagreeable; there may even sometimes be danger in
badly prepared sour milk. It is always an advantage in such matters to
understand the reason of things, and a few notes on the surrounding
conditions, and what has to be accomplished, may be of assistance to the
would-be experimenter.
The majority of intelligent people are now acquainted with the fact that
the germs of bacteria are to be found everywhere on the surface of the
earth, in air, and in water, and that they are the sole cause of the
decay of all manner of perishable articles.
The distribution is unequal--bacteria are much more plentiful where
there is decaying matter--in dirty houses, sewage, or other contaminated
water, etc. Milk is a splendid food for bacteria, and numerous varieties
multiply in it exceedingly, and many of these are injurious, producing
putrefactive changes which render the milk unwholesome, even poisonous
in some cases. Others are beneficial, and are absolutely necessary for
the souring of milk for making butter or cheese and for the ripening of
the latter. The soured milk which is the subject of this book is the
work of certain lactic-acid-producing bacteria, and the problem we have
before us is to encourage the growth of the latter to the uttermost and
to exclude the others.
As bacterial germs are present in the air and readily sow themselves
into any medium with which they come in contact, the first consideration
is to get good fresh milk which has been as little exposed to the air as
possible. The second is to conduct the experiment where the germs are
fewest, and in cleanly surroundings, far removed from decaying matter
and free from taints and smells.
[Illustration: FIG. 38.--Photo-micrograph of smear of
one-month culture of _Bacillus bulgaricus_. In spite of
its age, the culture is perfectly free from any foreign
organisms, which would otherwise lower its value for the
preparation of soured milk, and might, indeed, make it
directly injurious.]
[Illustration: FIG. 39.--Photo-micrograph of culture of
_Bacillus bulgaricus_ in malt. In cases of acute
enteritis, where milk cannot be supported, the lactic
bacilli may be cultivated in malt, and administered to the
patient in this form, with occasional doses of syrup of
malt, in order to induce a vigorous growth of the lactic
ferments in the body.]
[Illustration: FIG. 40.--Photo-micrograph of smear from
milk that had been allowed to sour spontaneously. Ordinary
market milk is always subject to infection from the air,
milking vessels, manure, etc., and from these sources a
mixed bacterial flora arises, with the result that the
milk exhibits curdling, acidity, gaseous fermentation, or
mould growth, after being stored for a short time. This is
due to the action of sush bacilli, diplococci, yeasts, and
moulds as are shown in this illustration.]
However fresh the milk may be, it will contain useless or injurious
bacteria, and we must get rid of these before attempting to introduce
those whose growth we wish to encourage. This is effected by heat. All
the living bacteria and most of the germs are killed at temperatures
somewhat under the boiling point. Having sterilised the milk in this
way, it is necessary, as far as possible, to prevent the entrance of
fresh germs from the atmosphere, and we therefore let the milk cool down
in covered dishes. When the temperature descends to about 100° F. the
culture of the special bacteria is introduced, the covers are replaced,
and the milk vessels maintained at or near this temperature for twelve
hours, when the soured milk is ready for use. It is not necessary to use
fresh culture every time--a little of the soured milk will take its
place, and this may be repeated as many as fourteen times before it is
necessary to start off again with a fresh culture. A great deal depends
on the care exercised and the freedom of the surroundings from bacterial
germs. Under the best conditions wild germs will gradually accumulate in
the soured milk, but their increase may be greatly delayed by attention
to the precautions mentioned. The ordinary souring of milk for butter
and cheese making is conducted in cool surroundings, as already stated,
because in such conditions the lactic-acid-producing germs increase
relatively faster than the wild germs, and so gain the upper hand, but
in the case of our special soured milk we kill out, practically, all
wild bacteria and germs, and the pure culture having the field to
itself, we can conduct the operation at a higher temperature where the
action of the bacteria is at its maximum, and so obtain the necessary
lactification in the minimum of time.
The appliances for the souring of milk on the domestic scale require
some consideration. We propose to describe the principal forms of
apparatus which have been put on the market for the purpose, and then to
give such suggestions as may assist the ingenious in making apparatus
for themselves. Those who wish for information on the subject of larger
apparatus will find it in the following chapter.
[Illustration: FIG. 41--Photograph of Agar Culture,
inoculated with a lactic powder offered to consumers under
a fancy name. Working on the assumption that the presence
of lactic bacteria is inimical to the growth of septic
organisms, this preparation has been placed on the market.
The plate shows, however an abundance of colonies of
foreign organisms--sporogenous bacilli, _Staphylococcus
pyogenes albus_, and _Staphylococcus pyogenes aureus_.
These organisms are shown in the appended
photo-micrographs, and constitute impurities in the
preparation.]
[Illustration: Spore forming bacillus]
[Illustration: _Staphylococcus pyogenes albus_]
[Illustration: FIG. 42--Photograph of Test Tubes of Sterile
Milk, inoculated with a tablet preparation said to contain
pure cultures. The darker liquefied portion of the
tube-contents is due to digestion of the curd by
proteolytic bacteria, thus indicating impure culture. Pure
cultures of lactic acid bacteria coagulate the milk
uniformly, but do not produce any subsequent change in the
appearance of the culture, even after several months.]
[Illustration: FIG. 43--Photograph of Test Tubes of
Sterile Milk, each tube having been inoculated with a
tablet of a preparation said to contain pure cultures.
Here, again, there is evident peptonisation of the curd,
thus indicating infection by proteolytic ferments.
Cultures from these tubes demonstrated the presence of a
foreign organism. Microscopical examination failed to
disclose the presence of _Bacillus Bulgaricus_.]
[Illustration: FIG. 44--Photograph of Test Tubes of
Sterile Milk, inoculated with a tablet of
"Lactobacilline." In contra-distinction to those shown in
Figs. 42 and 43, these tubes exhibit homogeneous curdling
of the milk without any subsequent digestion or
peptonisation of the coagulum. This is indicative of the
purity of the culture.]
The Society "Le Ferment" of Paris, which has been authorised by
Professor Metchnikoff to prepare and supply to the public his sour milk
culture, provides an apparatus for the treatment of the milk. It is
shown in Fig. 45, which consists of a double box having the intervening
space packed with a non-conducting material. It is provided with a
tight lid. Inside, there is accommodation for two milk vessels, each
with a capacity of about two thirds of a pint. The most difficult thing
in the souring of milk is to maintain the temperature as nearly at 100°
F. as possible while the culture is in action. This result is attained
by filling the vessel in the middle with boiling water. The insulated
walls hinder the escape of heat, and the quantity of boiling water used
is calculated to maintain the temperature steady for the twelve hours of
cultivation; but in cold, frosty weather it is necessary to refill the
central vessel with boiling water in the middle of the period.
[Illustration: FIG. 45]
The milk jars are washed with hot boiled water and turned upside down to
dry. They should not be wiped with a cloth. Boil the milk to be treated
for ten minutes, stirring it to promote evaporation, as it is
advantageous to have it in concentrated form. Cool rapidly to 100° F. by
placing the boiling vessel in cold water, add to each bowl one third of
a tube of the culture in powder form, fill up with the boiled and cooled
milk, stir well and cover. Place the jars in the box and fill the
central vessel with boiling water, shut the lid tight, and do not open
it (unless a fresh charge of boiling water is needed) for ten or twelve
hours, when it will be ready for use. If the liquid culture is used (one
small phial for each bowl) the milk should be cooled to 86° F. instead
of 100° F., as with the powder. The culture is also supplied in tabloid
form. The powder and tabloids keep well, but the liquid can only be
relied on for about two months. The milk prepared as above should be
stored in a cool place, the lids being kept on the bowls. It is good for
about two days, after which it becomes too sour. It can be eaten with
sugar, which not only sweetens it but is beneficial in affording
additional suitable food for the acid-producing bacilli. If fresh milk
cannot be had, condensed, sterilised, or pasteurised milk may be used,
but, of course, fresh milk is best. Condensed milk should be diluted
with two parts of boiling water and then treated like ordinary milk.
An apparatus on similar principles is sold by the Maya Bulgare Company,
Ltd., and is illustrated in Fig. 46.
[Illustration: FIG. 46--Soured Milk Apparatus of the Maya
Bulgare Company, Limited, consisting of an insulated box,
hot-water vessel, and covered vessels containing the milk
and culture. The apparatus consists of cabinet in deal,
Maya Bulgare ferment in 20-dose bottles, Maya Bulgare
ferment in 100-dose bottles, compressed Maya Bulgare
tablets in boxes of 8 tubes, Maya Bulgare caramels in
boxes of 40, reduced milk, china funnels, and
thermometers.]
The box is insulated, but the door is on the side, the hot water vessel
is underneath, and the covered vessels containing the milk and culture
are placed on a shelf above. In the front of the illustration are shown
the various packages in which the liquid and powder cultures are put up.
The procedure is exactly the same as with "Le Ferment" apparatus.
Lactic Ferments, Limited, make use of a different principle to maintain
the temperature steady during the lactifying period. Their apparatus
(Fig. 47) consists of a water vessel mounted on a stand. The milk
vessels (tumblers) are placed in the water, and the temperature
maintained at the proper figure by a small night light burning
underneath. It is recommended that the milk should be placed in an
earthenware jar or jug, which is stood in a pot of water kept boiling
for an hour. After cooling add from three to six previously crushed
tabloids of culture, and stir well with a glass rod which has been
sterilised in boiling water. The milk is then transferred to three
tumblers, which it should fill, and these are put into the water vessel,
the water in which should be at about 100° F., and the night light
started.
[Illustration: FIG. 47]
Messrs. Allen & Hanbury, Limited, also make use of the night light to
maintain the proper temperature during incubation in their "Sauerin"
apparatus (Fig. 48).
No water, however, is placed in the metal container. The procedure is
the same as that already described, and both tablet and liquid pure
cultures are supplied. For children it is recommended that the
incubation should occupy from three to four hours only, in other cases
eight to ten hours. Grated nutmeg, ground cinnamon, or other flavouring,
and cream may be used with the soured milk.
The night light is also employed in the "Veronelle" apparatus of Messrs.
Clay, Paget and Company, Limited (Fig. 49).
[Illustration: FIG. 48.--Messrs. Allen & Hanbury's Soured
Milk Apparatus. They maintain the temperature by means of
a night light, and the culture they use they call
"Sauerin."]
[Illustration: FIG. 49.--Vironelle Apparatus for souring
milk, made by Messrs. Clay, Paget & Company, Limited. The
milk in this case is placed in an earthenware jar, and is
sterilised by placing in a saucepan of water and boiling
it. The culture is added after cooling, the period of
incubation being about six hours.]
The containing vessel is of tin or aluminium, and has two stands, the
high one for hot and the low one for cold weather, as in the latter
case greater heat is needed to maintain the incubating temperature. The
milk is placed in an earthenware jar and is sterilised by placing it in
a saucepan of water and boiling it; continuing the boiling for half an
hour. It is allowed to cool to about 98° F., and placed in the
incubator, culture added, and the lamp lighted, the cover of the
incubator being kept on. The period of incubation is given as six hours.
To prepare the next day's supply a tablespoonful of the soured milk is
retained and used instead of the culture. This may be continued for
fourteen days, when a fresh start with culture is necessary. The soured
milk will keep for thirty-six hours. Capacity, one and one half and two
pints; also a large size for family use.
For the preparation of soured milk on a small scale, one of the various
forms of vacuum flasks now on the market may be used with satisfactory
results. A little cold water must be poured into the flasks, and warm
water added, until, by means of three to four changes, boiling water can
be safely poured in without cracking the flask.
This boiling water must be allowed to remain in for about twenty
minutes, and then replaced by freshly boiled milk that has been cooled,
so that its temperature in the flask is about 105° F. The culture of
lactic organisms should then be added, the opening of the flask plugged
with clean cotton-wool, and the cap screwed on.
In an actual test, the temperature of the milk placed in such a flask
was 105° F., at 7.30 P.M., and had dropped to 93° F. by 9 A.M., the
following day. The milk was curdled, and possessed the normal acid taste
of such cultures.
The different types of apparatus are all quite simple, and it would be
easy to make something at home. Get two round tins, the one less in
diameter by from two to three inches than the other, put one or two
pieces of wood across the bottom inside the larger tin, and fill up the
space between with cotton-wool, which is an excellent non-conductor of
heat. Place the smaller tin centrally inside the larger one. Fix three
or four distance pieces of wood in the space between them, fill up with
cotton-wool, leaving a little space at the top to permit the lid of the
smaller tin to be fixed on. The boiling-water vessel may be a tin
saucepan with a lid, but no handle, and its proper place would be on the
bottom of the inner tin. A tripod stand made of three pieces of wire
bound together, and with legs reaching past the hot-water vessel to the
bottom of the tin, would support a false bottom of tin forming the shelf
on which the vessels of milk to be treated would rest. These might be
tumblers covered with tin lids. To prevent radiation through the lid of
the inner tin, a thick pad or hood of cotton-wool packed between cloth
would be placed over the top. A little experimenting would be necessary
to determine the quantity of boiling water required to maintain the
proper temperature.
The soured milk obtained in the above manner is of the consistency of
ordinary buttermilk; a separation of whey frequently takes place, and
this may be poured off if desired. The taste and flavour should be
pleasantly acid and agreeable, and both are distinctive enough to give a
good idea of the purity of the product. In many places a more
concentrated article is made by boiling down the milk to one half or one
third of its bulk, and then fermenting it in the ordinary way. A kind of
thick pudding is thus obtained, which is highly recommended both as an
agreeable article of food and as a stronger medium for the support of
the germs it is the purpose of the sour milk treatment to introduce
into the digestive system.
The cultures for making soured milk can now be had from all the leading
wholesale and retail chemists, with directions as to the quantities to
be used.
It is very necessary that the milk used should be not only fresh and
good, but also free from chemical preservatives. The effect of these is
to inhibit the growth and development of bacteria, and they have
therefore an injurious influence on the special lactifying germs it is
our object to cultivate. Preservatives are now not nearly so much used
as they were, a few years ago, and there should be no difficulty in
obtaining milk free from them.
For keeping both fresh and soured milk good a small ice-chest is an
excellent device. The germs which are continually dropping into milk
kept in open vessels in the air, even in cleanly surroundings, are
mostly kept out in the close ice-chest, and the low temperature prevents
in a natural way the development of the bacterial germs already in the
milk. For the preservation of all kinds of foods the ice-chest is a
capital investment, not to mention the benefit of having cooled drinks,
etc., as required. They manage things well in this respect in the United
States, where ice is regarded as a necessity in the summer time by even
the poorest people, and is delivered with the same regularity as the
milk.
It is necessary to utter a word of warning as to certain forms in which
the sour milk bacillus is being offered to the public. It is being
compounded with sugar, chocolate, and other articles, and sold in the
form of sweets, etc. There is no reliable proof that these preparations
are valuable. Certainly, sugar is a medium in which the lactifying germs
can live, but the quantity so introduced into the system must be very
small compared with what is obtained from properly fermented milk. It
takes some time, even with strong cultures, to fix the acid-producing
germs in the large bowel where they are wanted, and until proper
evidence is forthcoming that confectionery preparations are efficacious
we would recommend that only the regularly fermented milk be used. It
would save trouble, no doubt, to treat oneself with a few chocolate
creams containing the necessary germs daily, but if the matter is taken
up seriously it will be better to take some pains and stick to methods
the efficacy of which has been demonstrated, leaving the others until
their _bona fides_ has been proved. There are always enterprising firms
who are prepared to simplify things for us, but we must make sure that
their simplifications are warranted.