THE PREPARATION OF SOURED MILK IN THE DAIRY
There is a tendency in certain medical quarters to discourage the use of
soured milk "made for profit." This view leaves out of account the fact
that besides being of value in medicine, the article in question is also
an excellent food, which, as we have seen, has been consumed by
multitudes of people for ages in many parts of the world. There seems
also to be satisfactory evidence that a larger percentage than usual of
the people who make soured milk a staple of diet attain to a ripe old
age. How does it become such a dangerous thing the moment the doctors
get it into their hands? Of course if a man has an acute disease he
places himself entirely in the hands of his medical man, and eats what
is prescribed for him, or at least he ought to do so, and if he makes
such a submission he is entitled at least to the comfort of being able
to feel that his doctor is free from unreasonable prejudices. For the
implication that an article "made for profit" is naturally suspect casts
an unwarranted stigma on a large number of honourable people. There are
dishonest tradesmen just as there are dishonest and careless doctors,
but to saddle a whole class with the offences of a few would not be a
justifiable proceeding in either case. Besides, it is not to the
interest of the manufacturing chemist or the dairyman to turn out
spurious cultures or bad soured milk, and on the whole we see no reason
why they should not engage in the business.
The widespread use of soured milk in other countries as a regular
article of diet seems to indicate that all manner of people, except
those suffering from diseases which necessitate medical regulation of
diet, might with probable benefit to themselves add this article to
their food list; and it looks as if a good many of them intend doing so,
even if scandalised doctors threaten "to abandon the cure."
The dairyman who knows his business does not need to be told of the care
which is necessary to keep milk in good condition. The merely commercial
consideration of avoiding loss has made him ready to inquire into the
best means of prolonging the life of milk as a merchantable article.
For a time he relied on chemical preservatives, but their day is now
almost over, and filtration, pasteurisation, and cold storage have taken
their place. Any one conversant with the trade knows how widely these
methods have been adopted of late years; we may, therefore, assume that
the average dairyman has at his command milk suitable for the incubation
process.
The demand for soured milk is not as yet a very large one, and the
apparatus so far developed for its production is meant for the treatment
of small quantities. After describing the principal appliances at
present in the market we propose to make some suggestions as to the
construction of larger apparatus.
A firm which has given great attention to the question of maintaining
fixed temperatures is that of Messrs. Charles Hearson & Co., Ltd. Their
incubators for chicken hatching are known all over the world; and their
appliances for biological incubation are very generally used in
bacteriological laboratories. With such experience it was natural that
they should turn their attention to soured milk apparatus, and the
result is the "Lactobator" (Figs. 50 and 51).
[Illustration: FIG. 50.--"Lactobator" made by Messrs.
Charles Hearson & Co., Limited, which is used for the
incubation of pure culture in milk in a fairly large way.
The illustration shows the "Lactobator" closed.]
[Illustration: FIG. 51.--Messrs. Hearson & Company's
"Lactobator," showing the internal arrangements.]
A copper vessel made to contain water has placed in it a stoneware jar
which holds two gallons of milk; on the top is a lid which carries a
thermometer for indicating the temperature of the milk. Heat is supplied
by a gas ring under the copper vessel; and in the gas supply is the
patent thermostat made use of by Messrs. Hearson also in their
biological and poultry incubators, in which a capsule containing a
liquid arranged to boil at a certain predetermined temperature is the
regulating factor. When the liquid boils, the capsule expands, and by
certain mechanical devices regulates the gas supply so as to produce
exactly the temperature required.
The procedure is as follows: The jar is filled with milk, and water is
run into the copper vessel by the funnel until it runs over at the
overflow pipe. The thermostat is lifted off and the full gas supply
allowed to pass to the burner, the temperature of the milk brought up to
180° F. and maintained for half an hour at this figure. The gas is then
turned off, and cold water run through the funnel until the temperature
of the milk registers 95° F. The culture is added, the lid replaced, and
the thermostat put into the pocket at the side of the vessel; the gas
relighted, and when the temperature reaches 100° to 106° F. the
capsule of the thermostat will expand and close the gas to a peep, which
is just sufficient to maintain the temperature within the above limits.
After eight hours the incubation is completed.
Edgar's patent apparatus, the "Lactogenerator," as provided by the Dairy
Supply Co., Ltd., is shown in Fig. 52.
[Illustration: FIG. 52. Edgar's "Lactogenerator"]
The milk is placed in a tinned copper-jacketed vessel and water run in
through a vertical pipe until it runs off at the overflow. Two gas
connections are required with cocks on each, the one to heat up the milk
to the boiling point and maintain it at this for thirty minutes. A
skimmer which has been placed in the milk lifts out the coagulated
protein and albumen which rise to the top. The cock is then shut and
cold water run through the jacket till the thermometer shows 90° F.,
when the culture is added, and the other gas supply with the regulator
turned on, and the temperature is automatically maintained at about 90°
F. Time of incubation eight to nine hours. It is recommended to turn
cold water into the jacket at the end of the period to prevent
overincubation.
A somewhat similar apparatus is that of the Willows Refrigerating Co.,
Ltd. (Fig. 53), with the exception that it has no automatic heat
regulator. It is made of tinned steel, and the operations are the same,
but the sterilising temperature (obtained by a gas ring or hot plate) is
given as 180°, and the incubating temperature 100° to 104° F. for a
period of twelve hours. Presumably this temperature is maintained by a
small gas jet or other similar source of heat. The capacity is two
gallons.
[Illustration: FIG. 53
Apparatus of the Willows Refrigerating Co., Ltd.]
In the apparatus hitherto described the milk is sterilised in bulk, and
is filled into bottles or jars after incubation, which is not a
desirable thing to do, unless the soured milk is for immediate
consumption, as there is likely to be contamination with injurious germs
from the atmosphere. In the domestic apparatus the milk is usually
incubated in covered jars in which it can be kept until required for
use, and the practice on the larger scale should be the same.
The Dairy Outfit Co., Ltd., have recognised this in their "Lacto"
apparatus (Fig. 54).
[Illustration: FIG. 54
"Lacto" Apparatus of the Dairy
Outfit Co., Ltd.]
A cylindrical vessel is set loosely on a stand, beneath which is a lamp
calculated to maintain the incubating temperature. The milk is placed in
bottles with metal screw tops, and these are put into the cylindrical
vessel; water is run in round them through the side funnel, the vessel
lifted off the stand, and heated to sterilising point on a stove. Cold
water is then run in through the funnel until the temperature is low
enough for incubation. Culture is added to each bottle and the lids
screwed on, the vessel lifted on to its stand, and the lamp lighted. The
cover of the apparatus has a thermometer fixed on it.
On the large scale the treatment of the milk would take place entirely
in the jars in which it would be sent out, and the sterilisation and
incubation would be conducted in different pieces of apparatus. The
sterilisation would be effected either (1) by direct steaming, or (2) by
hot water heated by steam. Fig. 55 shows the first type of
sterilisation. The tank is of wrought iron or steel with strengthening
pieces of angle iron. The door, with pulleys and counterweight for easy
handling, is fastened steam-tight by hinged bolts. The apparatus is
mounted on a stand at a convenient height for handling the bottles; and
in front is another stand with channel iron rails to take the waggon in
which the bottles or jars to be sterilised are packed. When the door is
fast, steam is turned on, and regulated to produce the proper
temperature by the thermometer fixed in the shell, in which a pressure
gauge is also secured. After sterilising, the door is opened and the
waggon drawn forward to the outside, allowed to cool, or removed
elsewhere to cool, and allow space for a new charge.
[Illustration: FIG. 55.--Sterilising Apparatus for
sterilising milk on the large scale. The bottles of milk
are sterilised, and the culture can then be added, and the
incubation allowed to proceed in an insulated chamber.]
The second method of sterilising is by hot water, as in Fig. 56. The
bottles or jars are placed on a perforated false bottom in the
rectangular tank, water run in up to the necks, and steam turned on; the
lid is fastened with hinged and hooked bolts; a thermometer fastened in
the lid, and with a long stem enclosed in metal, indicates the
temperature. At the end of the sterilising process cold water is turned
on, and at the same time the overflow water cock is opened; the cold
water gradually reduces the temperature, and the incubating point is
quickly reached.
[Illustration: FIG. 56 Another Method of Sterilising
(Dairy Supply Co., Ltd.).]
Incubation in bottles or jars, sterilised in these ways, can best be
conducted in an insulated room, with say, six inches of silicate cotton,
granulated cork, or washed cow hair packed between two-inch by six-inch
battens, covered with matching on either side, and lined with sheet
zinc. It would be an advantage to have an air-lock or anteroom into
which the waggons or trays of sterilised jars could be run, and the door
of the anteroom closed before the door of the insulated room is opened.
This would tend to prevent variations of temperature in the room, and
also, by checking free communication with the outside air, decrease
contamination. The waggons of jars would be run in, and culture added to
each jar by a sterilised pipette. The atmosphere of the room would be
kept pure by running in air frequently through a filter of moist
cotton-wool by means of an electric fan, and at intervals the interior
would be sterilised by the use of formalin vapour.
[Illustration: _Details of an American Apparatus for
Preparing Soured Milk_
FIG. 57
The figures give diagrams A, B, C, and D of an apparatus
useful for the preparation of lactic foods. The incubating
can A, is made of block tin, and is intended to contain
the milk. B, the warm water container, should be a stout
walled vessel with a circular aperture in the lid, through
which the incubating can may be passed, and clamped down
as in C.
B is fitted with three stout iron legs, which should be
sufficiently long to allow of a small lamp or gas-jet
being placed beneath the container to maintain a uniform
temperature.
D gives an external view of the apparatus.
For the preparation of soured milk, separated milk is
placed in the incubating can, and heated up to 100° C.
(212° F.) for thirty minutes. It is then allowed to cool
to room temperature, and the culture, or tablet containing
the lactic acid bacteria, is then added, and thoroughly
stirred for a minute or so. The can is then immersed in
the warm water container and kept at a temperature of 86°
F. to 104° F., according to the organisms used, for ten to
twelve hours. By the end of this time the milk ought to be
converted to a jelly-like mass, and after being stirred
vigorously for a short time, may be cooled on ice, and is
then ready for consumption.]
The incubating temperature could very conveniently be maintained by an
electric radiator, and as the insulation would largely prevent leakage,
the amount of electric current used would not be large. The regulating
apparatus might consist of a thermometer with platinum wires fused
through the stem at the proper temperature, say 100° F. When the mercury
rises to this figure it will complete the circuit of a battery which
will actuate certain well-known devices for turning off the current
which actuates the radiator. In this way a very fine automatic
arrangement would be achieved. Steam pipes might be used instead of the
radiator, and the thermometer above described could be used in this case
also, with appliances to cut off the steam.
On the large scale, labour-saving appliances, such as the mechanical
brush jar and bottle washer, and the automatic filler for jars or
bottles, would be employed, and an overhead trackway for carrying the
trays of jars from the steriliser to the incubator would be a great
convenience. A further adjunct of considerable importance would be a
cold room, worked either by ice or a refrigerating machine, in which the
jars could be stored after incubation, so as to arrest the process of
lactification, and maintain the soured milk in good condition until
required for use.