246 BACTERIA IN MILK AND MILK PRODUCTS 



satisfactory. A frequent method of testing has been to divide a 

 certain quantity of cream into two parts : one part inoculated with 

 the culture, and the other part left uninoculated. Both have then 

 been ripened under similar conditions, and churned in the same way ; 

 the differences have then been noted. It is interesting to know 

 that, as a result of the year's experience, creameries have been able 

 to command a price varying from half a cent to two cents a pound 

 more for the " culture " butters than for the uninoculated butters. The 

 method advised in using this pure culture is to pasteurise (by heating 

 at 155F.) six quarts of cream, and after cooling, to dissolve in this 

 cream the pellet containing bacillus No. 41. The cream is then set 

 in a warm place (70 F.), and the bacillus is allowed to grow for two 

 days, and is then inoculated into twenty-five gallons of ordinary 

 cream. This is allowed to ripen as usual, and is then used as an 

 infecting culture, or " starter," in the large cream vats in the pro- 

 portion of one gallon of infecting culture to twenty-five gallons of 

 cream, and the whole is ripened at a temperature of about 68 F. for 

 one day. The cream ripened by this organism needs to be churned 

 at a little lower temperature (say 52-54 F.), but to be ripened at 

 a little higher temperature than ordinary cream to produce the best 

 results. Cream ripened with No. 41 has its keeping power much 

 increased, and the body or grain of the butter is not affected. More 

 than 200 creameries in America used this culture during 1895, which 

 proves that its use for the production of flavour in butter is feasible 

 in ordinary creameries, and in the hands of ordinary butter-makers, 

 provided they will use proper methods and discretion. More recently, 

 pasteurisation has fallen into abeyance, and the use of artificial 

 cultures is said to have declined in America. In England, with few 

 exceptions, practically nothing has been done in a commercial way 

 in the direction of artificial " starters." 



2. Bacteria in Cheese-Making- 



The cases where it has been possible to trace bacterial disease to 

 the consumption of butter and cheese have been rare. Notwith- 

 standing this fact, it must not be supposed that therefore cheese 

 contains few or no bacteria. On the contrary, for the making 

 of cheese bacteria are not only favourable, but actually essential, 

 for in its manufacture the casein of the milk has to be separated 

 from the other products by the use of rennet, and is then col- 

 lected in large masses and pressed, forming the fresh cheese. In 

 the course of time this undergoes ripening, which develops the 

 peculiar flavours characteristic of cheese, and upon which its value 

 depends. 



We have said that the casein is separated by the addition of 



