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 hj 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. Whey 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 fireless 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 fireless cooker is used the plates or 
