USE OF BACILLUS BULGARICUS IN CHEESE STARTERS. 11 
HOW TO SECURE CULTURES. 
The problem of securing cultures of Bacillus bulgaricus for mak- 
ing starters will, of course, be an important one. It would be de- 
sirable to have a commercial source from which the active, pure 
cultures could be obtained, but it will probably be some time before 
cultures can be obtained in this way. In the meanwhile a number 
of sources are open. Cheesemakers have, in fact, been using B. bul- 
garicus starters unconsciously, which indicates that this bacterium 
is ordinarily present in the milk or whey of all factories. This can 
be verified by allowing a sample of whey to stand for about 48 hours 
at 100° F. If an active culture of bulgaricus is present the whey will 
become so sour that it can early be detected by smell. It will be best, 
however, for the cheesemaker to provide himself with an acidimeter 
outfit to test the strength of the culture. This apparatus is simple, 
easy to operate, and can be obtained for less than $5. Its cost may be 
saved on one cheese by insuring a good starter, and it can be used to 
advantage to find new cultures of bulgaricus. Unfortunately, al- 
though B. bulgaricus seems to be present almost uniformly in the 
whey in Swiss-cheese factories, it sometimes becomes suppressed, and 
under these conditions the rennet putrefies and may cause serious 
trouble in the cheese. 
The B. bulgaricus organism is especially likely to be absent entirely 
or lost in the early spring or late fall under present conditions. This 
condition has been noted by many European writers who have 
published discussions on the comparative merits of pure cultures of 
B. bulgaricus and commercial acid (which goes under the com- 
mercial name of casol) for insuring a whey rennet that will be free 
from undesirable gas formers. But there need be no trouble from 
this source when an active culture of bulgaricus is present and proper 
temperatures are used. When the temperature conditions are not 
favorable for the growth of B. bulgaricus other types of bacteria may 
crowd it out, or it will develop so slowly as to have no effect. This 
accounts in a large measure, probably, for the poor results with 
Swiss cheese in the colder seasons and for the fact that even in 
Switzerland great difficulty is experienced in making good cheese in 
winter. 
A good culture of B. bulgaricus should be able to produce a maxi- 
mum of at least 1.5 per cent of acid in whey when carried 48 hours 
at 100° F., with an inoculation of less than 1 per cent. In our experi- 
ence it was not difficult to find B. bulgaricus cultures that gave an 
acidity in whey of over 1 per cent in 24 hours carried at 100° F. 
However, it has been found necessary in the laboratory to change 
occasionally, as the cultures apparently become weakened. 
When cheesemakers either lose their cultures or find by the use of 
the acidimeter that their cultures have become weakened, a number 
