234 AGRICULTURAL BACTERIOLOGY. 



for about one day, when it is poured into a larger amount of 

 milk or cream, for the purpose of still further increasing its 

 bulk. The bacteria grow rapidly in the milk and there is thus 

 obtained a considerable quantity of typically ripened milk or 

 cream, thoroughly filled with the bacteria of the commercial 

 culture. The cream thus ripened is now used as a " starter" 

 in the general mass of cream to be churned, in proportions 

 which vary with the different butter-makers, according to ex- 

 perience, but which range from 2 to i o per cent. 



I. THE USE OF PURE CULTURES WITH PASTEURIZATION. 



Two quite different methods of using these starters have 

 been employed. The first method involves the pasteurization 

 of the cream before the culture is added. The cream is pas- 

 teurized at a temperature of 155 F. to 165 F. for a few mo- 

 ments and then cooled. This temperature destroys most of 

 the bacteria present and prepares the cream so that the pure 

 culture, when added, has an opportunity to grow unhindered 

 by the numerous bacteria which were originally present. 



This was the original method of Storch, and is that which 

 has been quite generally adopted in northern Europe. Start- 

 ing in Denmark it has, in that country, become very popular, 

 and at the present time practically all the butter of that great 

 butter-making country is made by the use of pasteurization, 

 followed by inoculation with commercial cultures. The object 

 of this is two-fold. In the first place the pasteurization of the 

 milk received at the creamery is generally adopted for the 

 purpose of decreasing the danger of distributing tuberculosis 

 among the farms. There is a law in Denmark requiring the 

 pasteurization of all milk which comes to a creamery. This 

 law has been introduced as an attempt to check the spread of 

 bovine tuberculosis which has become very prevalent in Den- 

 mark. The pasteurization makes it necessary to inoculate the 

 cream subsequently with some form of culture. Secondly, 



