The Bacillus of Long Life / A Manual of the Preparation and Souring of Milk for Dietary Purposes, Together with an Historical Account of the Use of Fermented Milks, from the Earliest Times to the Present Day, and Their Wonderful Effect in the Prolonging of Human Existence

by Loudon M. Douglas

Pasteuriser

Fig. 8.—The milk enters from the bottom and circulates to the top of the inside cylinder, which is paraboloidal in construction. It is heated as it passes through the apparatus, and is discharged at the top at a temperature of 176° F.

The centrifugal action is sufficient to raise the milk some three to four feet, through a tube, and this is taken advantage of so as to cause the milk to flow over a conical cooler, described as a primary cooler, and in which water is made to circulate. As the hot milk descends over the conical cooler it gives up most of its acquired heat to the water, and, in practice, is reduced in temperature to within 4° of the temperature of the water.

Below this primary cooler is fixed a cooler of the same size and shape, which is termed a secondary cooler. In it, brine at a temperature of about 35° F. is circulated from a refrigerating machine, and, as the milk falls over the secondary cooler, it is cooled to a temperature of about 40° F., when it may be looked upon as being pasteurised and free from all pathogenic organisms, in which state it will keep for a considerable length of time.

It is desirable that the milk should, as soon as possible after the cooling takes place, be delivered to the consumers, and be kept under cool conditions, either in bottles or in a closed vessel covered over with muslin, so as to keep out specks of germ-laden dust.

Briefly speaking, the foregoing is an outline of what is carried on in the ordinary dairy practice.

There are many modifications of this practice, such as the introduction of regenerative heaters, so as to utilise a portion of the heat of pasteurisation, which would otherwise be wasted.

In some cases, again, it is considered necessary to conduct the primary and secondary cooling over coolers furnished with mantles, so that the atmospheric bacteria which are everywhere present should be shut off from the falling milk.

Ordinarily, however, the equipment for a town's dairy consists of:

1. Steam-boiler to generate steam for pasteurising, scalding, etc.