The accompanying table gives results that were obtained in the testing of one of the continuous types of machines. The machine in question required about three hundred pounds of milk to fill it and was supposed to handle 1,000 pounds per hour. Thus theoretically it should require twenty minutes for any portion of the milk to pass through the machine. As will be seen from the data, some of the milk passed through within seven minutes after the water was shut off and the milk turned on. The figures also show that not all of the water had been replaced by the milk in even 45 minutes. In actual practice like results will be obtained, and a portion of the milk will be heated to the temperature employed but a short time. In this, the vegetating bacteria will not be wholly destroyed. ========================================================= Trial | |Per cent of fat in milk coming from | | machine at following times |Per cent|--------------------------------------- | of fat| MINUTES | in milk|--------------------------------------- | | 7 | 11 | 15 | 19 | 23 | 27 | 36 | 47 --------+--------+----+----+----+----+----+----+----+---- No. I | 4.0 | 0.2| 0.8| 1.6| 2.0| 2.4| 2.6| | No. II | 3.8 | 0.2| 0.6| 1.5| 1.8| 2.2| 2.6| 3.0| 3.4 No. III | 3.5 | 0.7| 1.9| 2.4| 2.8| 2.8| 3.0| 3.4| 3.4 ========================================================= =Pasteurization of small quantities of milk.= It is often desirable to treat a small quantity of milk for home use, in which case the commercial types of pasteurizers are out of the question. This treatment can be done in a number of ways, consideration always being paid to the manner of heating which should be done under such conditions, as have been shown to be necessary for efficient pasteurization. Milk may be heated in tall, narrow cans which are placed in hot water. In the household, milk may be treated by placing the filled bottle in a pail having a false bottom so the bottle shall not be broken when the pail is placed on the stove. The pail should be filled with water so that its level is about the same as that of the milk. The water is then heated to the desired temperature, maintained for the requisite period of time, and is then cooled as rapidly as possible. During the heating, the mouth of the bottle should be covered, either with an inverted glass tumbler, or the paper cap may be left in place, simply punching a small hole through it so as to permit of the insertion of a thermometer. [Illustration: Fig. 30.--A Pasteurizer for Use in the Home. A milk bottle with a tumbler for a cover. The cover prevents the formation of the "scalded layer" on the milk during the heating and also protects the mouth of the bottle from dust.]