10 DEPARTMENT BULLETIN 319, U. S. DEPT. OF AGRICULTURE 
milk that is tainted or too old to be used for other purposes. Skim 
milk, partly skimmed milk, or whole milk, as desired, may be. used. 
A more nearly uniform product is obtained if the milk is pas- 
teurized. The scorched taste which results from pasteurization at 
a high temperature is not objectionable as it is obscured by the 
acidity of the sour milk. The time of the inoculation may be ar- 
ranged to suit the convenience of the maker and can be determined 
by experience in each case. By using the same culture and holding 
the temperature uniform, the amount of the starter can be adjusted 
to bring 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° to 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 con- 
traction and toughening of the curd. 
Buttermilk made in the usual way as a by-product of butter mak- 
ing, 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 Lactobacittios bulgaricus. Directions for the 
preparation of this culture will be found on page 12. 
This culture not only gives the buttermilk a sharper and more 
agreeable flavor, but on account of its viscous nature also gives it a 
smoother texture and prevents the separation of the curd from the 
whey. 
MAKING CULTURED BUTTERMILK IN THE HOME 
A more nearly uniform product can be obtained if the cultured 
buttermilk is made on a large scale. 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 
possible to make cultured buttermilk in the home by following in a 
small way the directions for making cultured buttermilk on a com- 
mercial scale. It is necessary first to obtain a culture or starter, 
which is merely milk containing the lactic-acid or sour-milk bacteria 
free or very nearly free from other kinds of bacteria. Lactic-acid or 
sour-milk bacteria are present in any normal milk, and it is only 
necessary to provide conditions favoring their growth to obtain 
them in a state of purity. This may be done by folio wing the direc- 
tions on page 9 for obtaining cultures for making cultured butter- 
milk on a large scale. When the culture is obtained it will not be 
necessary to carry a small culture to inoculate the larger quantity. 
When the culture is obtained the following process should be car- 
ried out: 
One quart of either whole or skim milk is heated in a double 
boiler for at least one-half hour. The milk is then allowed to cool 
to about 75° or 80° F. At this temperature the outside of the con- 
tainer will feel warm to the hand. One teaspoonful of the fresh 
culture is added and the milk is transferred to a bottle or covered 
