ARTIFICIAL RIPENING 195 



artificial cultures in use in Europe and America. They are supplied 

 in various forms, as milk-cultures in bottles, as powders, or as pastes. 

 Of the species which produce good flavours in butter, the majority 

 are found to be members of the acid-producing class ; but probably 

 the flavour is not dependent upon the acid. Moreover, the aroma 

 of good ripening is also probably independent of the acid produc- 

 tion. 



Methods of artificial ripeningr. — Of all the methods of ripen- 

 ing — natural ripening, the addition of "natural starters,'' the addition 

 of pure cultures with or without pasteurisation — there can be no 

 doubt that pure culture after pasteurisation is the most accurate 

 and dependable. The use of " natural starters " is a method in the 

 right direction ; though being mixed cultures they are not uniform 

 in action. In order to obtain the best results with the addition 

 of pure cultures. Professor Russell has made the following recom- 

 mendations : — 



1. The dry powder of the pure culture must be added to a small 

 amount of milk that has been first pasteurised, in order to develop 

 an active growth from the dried material. 



2. The cream to be ripened must first be pasteurised, in order 

 to destroy the developing organisms already in it, and thus be 

 prepared for the addition of the pure culture. 



3. The addition of the developing " starter " to the pasteurised 

 cream and the holding of the cream at such a temperature as will 

 readily induce the best development of flavour. 



4. The propagation of the " starter " from day to day. A fresh 

 lot of pasteurised milk should be inoculated daily with some of the 

 pure culture. In this way the purity of the starter is maintained 

 for a considerable length of time. Those starters are best which 

 grow rapidly at a comparatively low temperature (6o"-75° F.), which 

 produce a good flavour, and which increase the keeping qualities of 

 butter. Now, whilst it is true that the practice of using pure 

 cultures in this way is becoming more general, very few species 

 have been isolated which fulfil all the desirable qualities above 

 mentioned. In America starters are preferred which yield a 

 " high " flavour, whereas in Danish butter a mild aroma is desired. 

 In this country as yet very little has been done, and that on an 

 experimental scale rather than a commercial one. In 1891 it 

 appears that only 4 per cent, of the butter exhibited at the Danish 

 butter exhibitions was made from pasteurised cream plus a culture 

 starter; but in 1895, 86 per cent, of the butter was so made, 

 and now upwards of 95 per cent is so made. Moreover, such 



