24 BULLETIN 319, U. S. DEPARTMENT OF AGRICULTURE. 



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 while they may be convenient they are by no means essential. 

 For the smaller dairy the following procedure will probably be 

 found satisfactory : 



(1) Propagate a small culture from day to day as indicated in the 

 directions given above. 



(2) Carry in a similar way a culture of the ordinary sour-milk 

 organism, which may be obtained from many of the commercial 

 laboratories. 



(3) Thoroughly pasteurize the milk to be fermented. 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 by a 

 steam hose. If a larger quantity is made, one of the starter cans 

 used in creameries will be found convenient. These are essentially 

 cylindrical vats with mechanical stirrers and a jacket which can be 

 filled with steam for heating or water for cooling. The milk should 

 be held at a temperature of at least 180° F. for not less than 30 

 minutes. 



(4) Cool the milk to about 100° F. Draw off one-half and inocu- 

 late it with the culture obtained in (2). Inoculate the remaining 

 half with the bulgaricus culture obtained in ( 1 ) . The amount to be 

 added will depend on the quantity of milk to be fermented, the time 

 at which it is desired to have it curdled, and the temperature main- 

 tained during the fermentation. This can best be determined by ex- 

 perience. One pint should be sufficient for any amount between 10 

 and 20 gallons. 



(5) The milk inoculated with (2) may be held at ordinary room 

 temperature. Precautions must be taken to hold that part inocu- 

 lated with the bulgaricus culture at a temperature of 90° to 100° F. 

 for several hours. If the milk is in cans it may be set in a tub of 

 warm water. A large volume of milk in a warm room will maintain 

 the proper temperature. 



If one is unable to hold the milk at the desired temperature, the 

 amount of culture inoculation should be increased. 



(6) When the milk has curdled, which should be in 10 or 12 hours, 

 mix the two lots thoroughly by churning or stirring together, 

 bottle, and put on ice to check the acid formation. 



