192 ECONOMIC BACTERIA IN MILK AND MILK PRODUCTS 



cussing fermentation, so here also, the action is only beneficial if 

 it is stopped at the right moment. If, for example, instead of 

 being stopped on the second day, it is allowed to continue for a 

 week, the cream may degenerate and become offensive, and the 

 pleasant ripening aroma would be changed to the contrary. The 

 majority of the species of organisms found in cream are in- 

 different in their effect upon butter. About 25 per cent, of them, 

 perhaps, exert a favourable influence, some 10 to 15 per cent, 

 exerting a bad effect. Of the good flavour-producing bacteria, 

 the majority belong to the acid group. But no hard and fast 

 lines can be laid down. Some develop flavour with acid, others 

 develop aroma with flavour, and others develop aroma without 

 any special flavour. Many of the organisms producing a good 

 flavour in butter are very widely distributed, especially at certain 

 times of the year. It should be added that Babcock and Russell 

 have pointed out that enzymes are present in milk, and take some 

 share in the ripening of cheese. If such enzymes are present in 

 cream, as is likely, it is possible they play some part in cream 

 ripening. Hence cream ripening may be due to a double fermen- 

 tation, organised and unorganised.^ 



Bacteriologists have demonstrated that butters possessing 

 different flavours have been ripened by different species of 

 bacteria. Occasionally one comes across a dairy which seems to 

 be impregnated with bacteria which improve cream and give good 

 flavour. In other cases the contrary happens, and a dairy becomes 

 impregnated with a species having deleterious effects upon its 

 butter. Such a species may be favoured by unclean utensils and 

 dairying, by disease of the cow, or by a change in the cow's diet. 

 Thus it comes about that the butter-maker is not always able to 

 depend upon good ripening for his cream. At other times he 

 gets ripening to occur, but the flavour is an unpleasant one, and 

 the results correspond. It may be bitter or tainted, and just as 

 certainly as these flavours develop in the cream, so is it certain 

 that the butter will suffer. Fortunately the bacterial content of 

 the cream is generally either favourable or indifferent in its 

 action. Thus it comes about that the custom is to allow the 

 cream simply to ripen, so to speak, of its own accord, in a vat 

 exposed to the influence of any bacteria which may happen to 

 exist in the vicinity. This generally proves satisfactory, but it 

 has the great disadvantage of being indefinite and uncertain. 

 Occasionally it turns out wholly unsatisfactory, and results in 

 ^ Centralb.f. Bakt., Bd. iii., 1897, p. 615. 



