No. 1. DEPARTMENT OF AGRICULTURE. Mi 



produced, but the bacterial content of the milk as well. Good milk 

 should not contain a large number of organisms — 2,000 per c. c. 

 (cubic centimeter) being the limit. 



Of course it is understood that not every dairy farmer is or can 

 be so situated that he may produce milk in the above described man- 

 ner. The production of such milk is expensive and the producer 

 should be paid in proportion to the greater expense and care in- 

 volved. Milk when treated in this way sells for twice as much as 

 ordinary milk. The demand^, therefore, is somewhat limited, and a 

 special trade must be built up for it. 



CLARIFYING AND FILTERING, 



After milk is drawn it is sometimes subjected to treatment to in- 

 crease its keeping qualities. Foreign particles may be removed from 

 milk by straining, filtering or clarifying. Bacteria may be destroyed 

 by heating^ as in sterilizing and pasteurizing or by chemical treat- 

 ment, or they may be kept from developing by refrigeration. Chem- 

 ical treatment is neither legal nor legitimate, and should never be 

 resorted to. Aeration does not add to the keeping quality of milk, 

 but only serves to permit the escape of gases and disagreeable odors. 



Sometimes milk is passed through a separator before it is cooled. 

 This is called clarification. Many of the impurities are removed with 

 the separator slime. After separating, the milk and the cream are 

 remixed and cooled to 50 degrees. When milk is treated in this way 

 and kept cold, it will remain sweet for several days. Separators 

 intended for use as clarifiers sometimes have an arrangement for 

 re-mixing the skim milk and cream. The arrangement of the fat 

 globules is not the same in clarified milk as in the original. While 

 most of the dirt and one-third to one-half of the bacteria are thrown 

 out in the separator slime, the keeping quality of the milk is not 

 much increased. 



Filters for the purification of milk, by passing it through sand, 

 gravel or felt, under pressure, have been placed upon the market from 

 time to time, but have not come into general us^ owing to the diffi- 

 culty of keeping them clean. They remove only the larger mechani- 

 cal particles. Bacteria cannot be strained or filtered out as they are 

 much smaller than the fat globules. 



STERILIZATION. 



In order to thoroughly sterilize milk by heating, the temperature 

 must be raised to 212 degrees F. on several consecutive days. Such 

 treatment gives to the milk a cooked taste and renders it less di- 

 gestible. For these reasons it cannot be used in treating milk for 

 drinking purposes, and is useless in treating milk for buttermaking, 

 &■ will be shown later. 

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