BUTTER 225 



of the butter-maker, because the presence of lactic acid in the cream 

 helps him in four ways : 



1. It makes the churning easier and more complete. 



2. The butter keeps better. 



3. The yield of butter is greater. 



4. The flavour and aroma of butter are improved. 



But as cream is a splendid nutrient medium for all sorts of bacteria, it 

 will be seen that it must occasionally happen that undesirable bacteria 

 gain the upper hand, as a result of which obnoxious substances will be 

 formed, rendering the milk unpalatable, if not poisonous. 



The modern butter-maker leaves nothing to chance. He regulates 

 the souring in such a way that the risk of an undesirable fermentation 

 is reduced to a minimum. This regulation is called artificial souring, 

 and may be accomplished by one of the following ways : 



I. The Natural Starter Method. This consists in adding to the 

 ripening cream a small portion of cream from a previous favourable 

 ripening. If the ripening has been favourable on a previous occasion, 

 it follows that the predominant bacteria in that cream were good. By 

 setting aside, therefore, a portion of this cream and adding it to the 

 next ripening, a start is given to the same bacteria, arid so the chances 

 of another favourable ripening are increased. This "natural starter," 

 as it is called, may be cream taken from a very good dairy or from the 

 herd producing the best quality of cream. The method, however, has 

 one defect in not being always reliable, because, as the bacterial content 

 of the " starter " is not known and not regulated, there is always the 

 possibility of the presence in it of harmful bacteria which are liable to 

 drop in at any moment. Then if these multiplied, at the next ripening 

 the whole of the next batch of butter would be rendered valueless. 



The second and third methods consist in the employment of pure 

 culture starters. The starter is a pure culture of an organism which 

 is known to produce favourable changes in the cream. In debating the 

 choice of a starter, there are two points which have to be considered. 

 The butter-maker may elect to make sure that the souring takes place 

 along the right lines (second method), or he may leave the souring 

 partially to chance and employ a pure culture which ensures a splendid 

 aroma in the butter if the souring has been successful (third method). 



II. Pure Culture Method regulating the Souring of Cream. The 

 starter is prepared as follows : A small portion of cream is warmed up 

 to 60 C., then immediately recooled as quickly as possible. This kills 

 or weakens the bacteria already present in it. Then a pure culture of 

 the organism which is known to sour milk along the right lines is 



