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