98 EXPERIMENTAL DAIRY BACTERIOLOGY 



butter making was largely due to Storch and to Weigmann. 

 Beginning in 1890, the use of pure cultures has spread rapidly 

 and is now quite universally employed in commercial butter 

 production. 



On account of the difficulty and trouble the butter maker 

 encounters in selecting milk for the preparation of home- 

 made starters, and the lack of uniformity of product con- 

 nected with their use, the majority of butter makers prefer 

 to purchase the starter foundation. A number of firms are 

 engaged in the preparation and sale of pure culture or com- 

 mercial starters for butter making. 



These cultures are sold in liquid and dry forms. The 

 liquid starters usually consist of a milk culture of the organ- 

 ism. The dry starters are prepared by mixing with a liquid 

 culture in an actively growing condition some inert sub- 

 stance, as milk sugar, milk powder, etc., in order to absorb 

 the moisture of the culture and thus maintain the organ- 

 isms in an active condition. In liquid cultures deterioration 

 is rapid on account of the injurious effect of the by-products 

 of the bacteria themselves. In dry cultures deterioration is 

 due mainly to the influence of desiccation on the contained 

 organisms. The effect of desiccation on most lactic bacteria 

 is much less than that of the by-products (acid) ; hence 

 the starters in dry form can be kept much longer than in 

 liquid form. 



The important points to be noted in the examination of 

 commercial starters are : (1) purity ; (2) vitality and fermen- 

 tative power ; (3) preservation of original properties on prop- 

 agation ; (4) flavor-producing properties. 



Purity. The purity of a starter may be tested by preparing 

 from the original package lactose-agar and plain agar plate 

 cultures. A series of dilutions should be made in order to 



