224 BACTERIA 



in curing the cheese. Upon this basis a system of pure 

 starters has been adopted, the characteristics of which 

 must be as follows : (a) The organism shall be a pure lactic- 

 acid-producing germ, incapable of producing gaseous pro- 

 ducts; (b) it should be free from any undesirable aroma; (c) 

 it should be especially adapted for vigorous development 

 in milk. The starter may be propagated in pasteurised 

 or sterilised milk from a pure culture from the laboratory. 

 The advantages accruing from the uses of this lactic-acid 

 culture, as compared with cheese made without a culture, 

 are that with sweet milk it saves time in the process of 

 manufacture; that with tainted milk, in which acid develops 

 imperfectly, it is an aid to the development of a proper 

 amount of acid for a typical Cheddar cheese ; and that the 

 flavour and quality of such cheese is preferable to cheese 

 which has not been thus produced. Professor Russell is of 

 opinion that the lactic-acid organisms are to be credited 

 with greater ripening powers than the casein-digesting 

 organisms, but it must not be forgotten that these two great 

 families of bacteria are still more or less on trial, and it is 

 not yet possible finally to dispose of either of them. Mr. 

 F. J. Lloyd holds that though " the greater the number of 

 lactic-acid bacilli in the milk the greater the chance of a 

 good curd," still " this organism alone will not produce that 

 nutty flavour which is so sought after as being the essential 

 characteristic of an excellent Cheddar cheese." ' 



There are several difficulties to be encountered by dairy- 

 men starting a ripening by the addition of a pure culture. 

 To begin with, there is the initial difficulty of not being able 

 to pasteurise milk intended for cheese, as rennet will not 

 coagulate pasteurised milk (Lloyd). Hence it is impossible 



1 " Observations on Cheddar Cheese Making," Reports of Bath and West 

 and Southern Counties Society, 1898, pp. 163-171. Mr. Lloyd's Reports to 

 the West of England Society since 1892 contain various points respecting the 

 application of bacteriology to cheese-making. 



