CREAMERY BUTTER MAKING 91 



may be used as a starter. But in the case of unpasteurized 

 cream, even though the flavor is good, there are always 

 present some undesirable germs which will multiply in 

 each successive batch of cream or buttermilk used as a 

 starter, so that after a week's use the flavor may actually 

 be bad. Where cream is slightly off flavored and a por- 

 tion of this, or the buttermilk from it, is used as a starter, 

 it will readily be seen that the taint will not only be 

 transmitted but will multiply in the cream from day to 

 day. The use of either cream or buttermilk as a starter 

 is therefore never to be recommended. 



COMMERCIAL STARTERS. 



Commercial starters may consist of a single species 

 of lactic acid organisms, but usually they are made up 

 of a mixture of several species. These starters are pre- 

 pared in laboratories where the utmost precautions are 

 taken to keep them free from undesirable germs. The 

 methods by which the good bacteria are separated from 

 the bad are quite complicated and of too little practical 

 value to permit a discussion of them here. Suffice it to 

 say that such separation is possible only with the skilled 

 bacteriologist. 



Keith and Douglas each manufacture three different 

 cultures which are put upon the market in liquid form, the 

 liquid usually being bouillon, or beef extract, treated 

 with milk sugar. The development of the germs in this 

 medium is very rapid and the cultures should therefore 

 not be used later than ten days after they are sent out 

 from the manufacturer unless they are kept at low tem- 

 peratures. The reason for this is that the rapid growth 

 of the bacteria will quickly result in vast numbers of them, 



