22 DEPAETMENT BULLETIN 319, U. S. DEPT. OF AGRICULTURE" 
(about blood heat). At this temperature the container will feel 
warm, but not hot, to the touch. A considerable quantity of the 
culture is added to this milk. If it is in the form of tablets three 
or four should be used. 
The milk is transferred to a bottle or fruit jar or, better still, to a 
vacuum-insulated bottle, which has been rinsed with boiling water 
and kept overnight in a warm place. Good results may be obtained 
by placing the bottle or jar containing the milk in a dish of water 
warmed to about 100° F. The most favorable temperature for the 
fermentation is at or a little below blood heat. At a little higher 
temperature the organism grows faster, but the curd is likely to 
separate from the whey as a tough mass. At a lower temperature 
the growth ma} 7 be so slow that other bacteria gain the ascendency. 
By the following morning a thick, somewhat stringy curd with 
a sharp, acid taste should have developed. One teaspoonful of this 
curdled milk is added to from 1 pint to 1 quart of milk which has 
been heated in a double boiler, held at the boiling point for one-half 
hour, and then cooled. This milk is held as before, and the curd 
which has formed is broken up by being shaken vigorously in a 
fruit jar. 
This process may be repeated as long as the curdled milk has a 
smooth, acid curd free from undesirable flavors and particularly 
the yeasty flavor and odor characteristic of bread dough. The so- 
called Lactobacillus bulgaricus, under favorable circumstances, will 
suppress other bacteria by its vigorous acid formation, but yeasts 
are favored by the acid condition of the milk and sooner or later 
make their appearance. Every precaution should be taken to protect 
the milk from exposure to the air and to sterilize all utensils with 
boiling water. When evidences of yeast contamination appear it 
is best to start with a fresh culture. 
Yogurt may be made more palatable by adding to two parts of 
the yogurt one part of cold water, or, better still, cold-charged 
water, which can be bought in siphons at drug stores. Sugar and 
lemon juice or other fruit flavor, or chocolate sirup, may also be 
used for this purpose. The sugar should be added in the form of 
a sirup, as granulated sugar dissolves very slowly in the cold yogurt. 
In making yogurt on a large scale the process is not essentially 
different except that it is advisable to carry a small culture, about 1 
quart, to inoculate the milk to be made into buttermilk. Every 
precaution should be taken to maintain the purity of the culture. It 
is advisable to carry duplicate cultures independently so that a 
good one will always be available. 
Expensive outfits for making fermented milks are on the market, 
but although they may be convenient they are by no means essential. 
For the smaller dairy the following procedure will probably be 
found satisfactory : 
A small culture is propagated from day to day as indicated in 
the directions given above. In a similar way a culture of the 
ordinary sour-milk organism is carried. This may be obtained from 
many of the commercial laboratories. 
The milk to be fermented should be thoroughly pasteurized. If a 
small quantity — 5 to 10 gallons, for instance — is to be made, it may 
be done by holding a can of milk in a tub or vat of water heated 
