*6o CLEAN MILK 



simply of a quantity of sour milk or cream containing a great num- 

 ber of germs, suitable for ripening cream, which was added to fresh 

 -cream to quickly sour and ripen it, especially in cold weather. These 

 are called natural starters, and are still used extensively. To pre- 

 pare such a starter the milk is withdrawn from the cow in the most 

 cleanly manner; the milk is then separated and the skim milk is 

 collected in an absolutely clean vessel and set aside at a temperature 

 of 6o u to yo° F. to sour. This sour milk may contain all sorts of 

 germs, but if it is clean there are apt to be few miscellaneous germs 

 and these are likely to be crowded out by the growth of the lactic 

 acid germs, so that the result may be almost as pure a culture or 

 collection of lactic acid bacilli as is found in the commercial starters. 

 We quote the following from Farrington : 



The foundation material for both kinds of starters is usually skim milk. 

 "This is first freed from most of its bacteria by heating it to 180 deg. F. or 

 above, for at least one-half hour. It is a good plan to keep this hot milk well 

 -stirred and covered while it is being heated. After this period of heating, the 

 skim milk is copied. The cooling is usually done by setting the can of hot 

 skim milk into cold water. The quicker it is cooled the better. When the 

 temperature of the skim milk reaches 80 deg. F., it is then in condition to 

 receive either the pure culture which has been brought from the dealer, or 

 the sour milk which has been selected and allowed to sour naturally. 



The so-called commercial starters are made by' adding to about a gallon 

 of this skim milk a small quantity (about an ounce) of the pure culture which 

 has been brought from a dealer in this material. After the pure culture has 

 been added to the skim milk the mixture is kept at a temperature of about 

 80 deg. F. until the skim milk has become soured by the pure culture bacteria. 

 This preparation is sometimes called " startoline," and it may amount to 

 about four quarts of sour milk. This is added to a larger quantity of pasteur- 

 ized skim milk, which has been prepared by heating and cooling as previously 

 -described, and the mixture is allowed to stand at a temperature near 80 deg- 

 until it becomes sour and has an acidity of about six-tenths of one per cent.* 

 If the cream in which the starter is to be used is now ready, the starter may 

 be added to it in about the proportion of ten pounds of starter to one hundred 

 pounds of cream. A small quantity of this starter is saved each day and 

 added to a new lot of pasteurized skim milk. In this way the starter is car- 

 Tied on from day to day and a new lot for use in ripening cream is prepared 

 every day. 



The natural starter is made in exactly the same way as the commercial 

 starter, except that in place of the ounce of pure culture which is bought 



*See page 190. 



