CHAPTER VII
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).
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.
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.
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.
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).
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.
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.
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.
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.