BACTERIA IN FOODS 21$ 



which it has been emulsified. It is then placed in the cold 

 to set. The water may be now either centrifugalised or 

 placed in sedimentation flasks, and the deposit examined 

 for bacteria. 



The Uses of Bacteria in Dairy Produce. In considering the 

 relation of bacteria to milk we found that many of the 

 species present were injurious rather than otherwise, and 

 when we come to consider bacteria in dairy products, like 

 butter and cheese, we find that the dairyman possesses in 

 them very powerful allies. Within recent years almost a 

 new industry has arisen owing to the scientific application 

 of bacteriology to dairy work. 



As a preliminary to butter-making the general custom in 

 most countries is to subject the cream to a process of 

 " ripening." As we have seen, cream in ordinary dairies 

 and creameries invariably contains some bacteria, a large 

 number of which are in no sense injurious. Indeed, it is to 

 these bacteria that the ripening and flavouring processes 

 are due. They are perfectly consistent with the production 

 of the best quality of butter. The aroma of butter, as we 

 know, controls in a large measure its price in the market. 

 This aroma is due to the decomposing effect upon the con- 

 stituents of the butter of the bacteria contained in the 

 cream. In the months of May and June the variety and 

 number of these types of bacteria are decidedly greater than 

 in the winter months, and this explains in part the better 

 quality of the butter at these seasons. As a result of these 

 ripening bacteria the milk becomes changed and soured, and 

 slightly curdled. Thus it is rendered more fit for butter- 

 making, and acquires its pleasant taste and aroma. It is 

 then churned, after which bacterial action is reduced to a 

 minimum or is absent altogether. Sweet-cream butter lacks 

 the flavour of ripened or sour-cream butter. The process is 

 really a fermentation, the ripening bacteria acting on each 

 and all of the constituents of the milk, resulting in the 



