494 MANUAL OF MILK PRODUCTS 



the acidity to the curdling point at any definite time within 

 narrow limits. The temperature of the milk should be between 

 21° and 24° C. (70° and 75° F.). More rapid development of 

 acid can be obtained at higher temperatures, but at the lower 

 temperatures the lactic acid bacteria are more successful in 

 checking the growth of digesting and gas-forming bacteria. 

 At lower temperatures and with a slower development of acid 

 the casein is precipitated in a finer and more friable curd than 

 at temperatures inducing a more rapid acid production. As 

 soon as a fine curd has been formed the milk should be cooled 

 promptly to below 50° F. to prevent the contraction and tough- 

 ening of the curd. 



Buttermilk made in the usual way as a by-product of butter- 

 making, and especially buttermilk obtained by churning 

 pasteurized cream, is improved by mixing with it about 10 

 per cent of a skim-milk culture of the Bacillus bulgaricus. Di- 

 rections for the preparation of this culture will be found on 

 page 508. 



This culture not only gives the buttermilk a sharper and 

 more agreeable flavor, but on account of its viscous nature it 

 gives it a smoother texture and prevents the separation of the 

 curd from the whey. Detailed directions for the preparation 

 of buttermilk by this method may be found in a circular of the 

 Illinois Agricultural Experiment Station. 

 Making buttermilk in the home. 



A more nearly uniform product can be obtained if it is made 

 on a large scale, and if good buttermilk can be purchased from 

 a reliable milk dealer at a reasonable price, it is not advisable 

 to attempt to make it on a small scale. However, it is pos- 

 sible to make buttermilk in the home by following in a small 

 way the directions for making buttermilk on a commercial scale. 

 It is necessary first to secure a culture or starter, which is 

 merely milk containing the lactic acid or sour-milk bacteria 

 free or very nearly free from other kinds. These bacteria are 



