12 BULLETIN 148, U. S. DEPARTMENT OF AGRICULTURE. 



of ways are open to renew or secure more active ones. Securing 

 samples of whey from factories has proved to be the most satisfac- 

 tory way of renewing cultures. This would be an easy method for a 

 cheesemaker to follow. The Dairy Division often has samples of 

 whey sent from Wisconsin factories, and will send out a limited num- 

 ber of the most active bulgaricus cultures to those who are equipped 

 to use them and will report the results of their trials. Another way 

 would be to set individual samples of milk from patrons at the proper 

 temperature (about 100° F.) for five days and select the one that 

 developed the greatest acidity. Still another way is to grind up a 

 piece of Swiss cheese in whey and carry at a temperature of 100° F. 

 for five days. We have used this last plan on different occasions, but 

 it is open to two objections. The B. bulgaricus may lose its activity 

 by being carried in the cheese. Again, in preparing a starter in this 

 way the bacteria responsible for the eyes in the cheese grow with 

 the B. bulgaricus, and the result is a cheese with a decided tendency 

 to form too many eyes. This can in a measure be overcome by allow- 

 ing the acidity to develop to a high point, which, judging from some 

 of our results, kills the bacteria which form the eyes. 



In all the work reported here whey was used in preference to 

 milk for making the starter. It does not develop so high an acidity, 

 but it has two advantages which are very desirable in cheesemaking. 

 A milk starter contains casein coagulated with acid and therefore 

 contains a large part of the living bacteria which do not become 

 thoroughly distributed throughout the milk. Whej^ has neither of 

 these faults. It is possible also that whey would make a more satis- 

 factory starter for other purposes, though it might not furnish all 

 the qualities desirable in butter-making. 



KEEPING THE CULTURE AND STARTERS. 



Since Bacillus bulgaricus requires a temperature of about 100° F. 

 for rapid growth, the proper conditions are not hard to obtain in 

 summer, and have been supplied to cheesemakers as a rule in 

 their method of carrying their rennet, where the warm whey con- 

 taining the rennet is set above the fireplace or boiler, and as a result 

 the bulgaricus grows rapidly and provides a good starter. At 

 other seasons some extra means must be provided to insure the right 

 temperature throughout the period required for the starter to attain 

 a sufficiently high acidity. Perhaps as simple a method as any 

 would be a tireless cooker or a well-insulated box of any kind. A 

 square box insulated with granulated cork and with a receptacle 

 for holding the whey which just fitted the inside of the box proved 

 satisfactory for our work. If a tireless cooker is used the plates or 



