USE OP BACILLUS BULGAEICUS IN CHEESE STARTERS. 9 



provide some means of keeping the starters at a temperature high 

 enough to insure the growth of the B. bulgaricus. A well-insulated 

 box was made for this, somewhat on the order of a fireless cooker, 

 which maintained temperatures very satisfactorily on nights when 

 the outdoor temperature was below freezing. Considerable diffi- 

 culty with yeasts was experienced, making frequent changes of cul- 

 tures necessary, as noted on another page. The first six cheeses in 

 Table 4 turned out "nissler," which is an indication of undesirable 

 gas formation. In all the experiments except No. 14 the cheese was 

 made once a day, using a mixture of morning and evening milks. 

 The farmers made no pretense of cooling the milk, and as a very 

 large can holding about 200 pounds of milk is used, the large bulk of 

 milk cooled very slowly, even on frosty nights. The night milk with 

 this treatment had developed so much acid, or such . a growth of 

 lactic-acid organisms, that in one instance the whey contained 0.19 

 per cent of acid at the time the curd was dipped, whereas it should 

 have contained normally but 0.12 per cent. In all cases there was a 

 marked development of acid. From the results shown in Table 3, 

 where the sour-milk starter designated in the table as SM was used in 

 a commercial factory, it would appear that a high development of 

 acidity in the milk from the growth of ordinary lactic- acid formers 

 tends to give a " nissler " cheese. Apparently the milk must be sweet 

 when delivered or the B. bulgaricus starters do not suppress all 

 undesirable gas formers. 



When it was found to be impossible in the short time at our com- 

 mand to induce the farmers to cool their evening milk, they were 

 asked to deliver twice a day, as is the custom in the summer months. 

 The night milk was then cooled in a kettle by means of a coil through 

 which cold water was pumped. But as the temperature of the cooled 

 milk was not lower than about 68° F., it could not be said that the 

 milk was unusually well cared for. Beginning with experiment No. 

 7, for which the night milk was cooled at the factory, we had milk 

 sweet enough to work up in a normal manner, and the cheeses were 

 all perfectly free from undesirable gas formation. 



The milk delivered generally to the factory was not of the best 

 quality. The brick cheese made before these experiments was badly 

 gassy, and fermentation tests made with the milk of individual 

 patrons at short intervals during the experiments showed that more 

 than one-half of the patrons delivered gassy milk, some of the sam- 

 ples being very bad. It appeared that the starters were of great 

 assistance in overcoming serious trouble with the gassy milk. Ordi- 

 narily this factory would not have begun to make Swiss cheese for 

 a month later than it was made successfully in these experiments, 

 though the higher price of Swiss cheese is a great inducement to 

 make this variety rather than brick cheese. 



