488 MANUAL OF MILK PRODUCTS 



plicit in his statement that great care should be taken to 

 determine the abundance and purity of the desired organism. 

 Bacillus bulgaricus seems to be particularly sensitive to desic- 

 cation. When preparing the material in tablet form, there- 

 fore, a high percentage of the organisms is usually killed, 

 whereas foreign organisms commonly retain their viability. 

 Even when prepared with the best of care, such tablets lose 

 their efficiency so quickly that unless they are used within 

 a time limit of efficiency guaranteed by the maker the results 

 may be disappointing. 



It is very easy to test the purity and activity of these dried 

 cultures. Thoroughly pasteurize a small quantity (about half 

 a pint) of milk by holding it, in a bottle plugged with cotton, 

 at or near the boiling point for an hour or more. When this 

 has cooled, add two or three of the tablets and keep in a very 

 warm place overnight. It should not be below and may be a 

 few degrees above blood heat. If in this time the milk has 

 not curdled with a sharp, acid taste and without gas bubbles 

 and whey, there can be no reason for using these tablets except 

 the possibility that they contain the active element of the cul- 

 ture which retards the growth of other bacteria. The evidence 

 on this point is so inconclusive that it need not be considered 

 in this connection. 



All reliable manufacturers now place the date of manufac- 

 ture on each package and state the time within which the 

 tablets should be used. 



Buttermilk 



Buttermilk, properly speaking, is the by-product resulting 

 when milk or cream is churned for butter. It is the milk 

 remaining after the fat which collects in granules is removed. 

 If cream is churned when sweet the buttermilk does not differ 

 from ordinary skimmed milk, but if it is churned when sour 



