276 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



all the bacteria present in the cream and its associated milk 

 are destroyed by the process of Pasteurisation, and the 

 subsequent inoculation of the Pasteurised cream with a pure 

 culture of the necessary bacteria. 



The process of Pasteurisation consists in a rapid heating to 

 a temperature sufficient to destroy the majority, at any rate, 

 of the bacteria present, followed by an equally rapid cooL'ng 

 process. By this method the composition and flavour of the 

 cream is not appreciably altered. The pure culture to be 

 added is generally known as the ' starter.' The following is the 

 method described by the Danish bacteriologist Weigmann : — 



A quantity of sweet milk, amounting to about two or three 

 per cent, of the cream to be acidified, is heated to about 60° C. 

 and quickly cooled ; to it is added a pure culture which is 

 maintained by the addition of sweet Pasteurised milk from 

 day to day. A portion of the inoculated milk is added to 

 the cream, which is best prepared by cooling to a low tempera- 

 ture and then quickly warming up again to 16° or 20° C. 

 The ripening process is generally started in the evening, and 

 allowed to complete itself at a tsmperature of 15° to 20° C, 

 the cream being ready for churning on the following morning. 



The flavour of the butter produced depends on the particular 

 starter used. It does not appear certain whether one variety 

 of organism alone is concerned in producing specific flavours, 

 although all the organisms concerned probably belong to the 

 lactic acid producing species. At any rate one organism has 

 been found by Professor Conn in America which produces a 

 very excellent flavour. It was originally obtained from a 

 specimen of milk from Uruguay, South America, exhibited 

 at the World's Fair in Chicago. This baciUus is known as 

 No. 41, and by its use constant results have been maintained 

 on a very large scale. 



Although, as has been stated, the ripening of cream is 

 mainly produced by lactic acid bacteria, the precise chemical 

 changes, resulting in the production of a difierent taste or 



