354 BUTTER 



of which the following appear to be the most important, 

 since they are practically always met with in abundance 

 in rancid butter : 



1. One or two forms of lactic acid bacteria ; 



2. Oospora lactis ; 



3. Yeasts, some of which form rose or yellow colours 



on gelatine and agar ; 



4. Cladosporium butyri, a species of hyphomycete 



belonging to a widely distributed genus. 



Less frequently certain " moulds " (species of Mucor 

 and P enicillium) are present, as well as Bs. lactis aerogenes 

 and Bs. fl. liquefaciens. 



(ii) The Tallowy Flavour and appearance may be 

 brought about by the decomposition of the fats and the 

 production of free fatty acids. The cause of the change, 

 as already pointed out, is sometimes bacterial ; but in 

 other cases the tallowy taste and texture is the result of 

 purely chemical processes, namely oxidation and hydro- 

 lysis under the influence of light and moisture, especially 

 accompanied by somewhat high temperature. Storage 

 of the butter in a dark, cool, and comparatively dry 

 place will usually check this trouble. 



(iii) Turnip Flavour in Butter. When large quan- 

 tities of turnips are used for the feeding of cows the milk 

 becomes tainted, and the cream and butter obtained from 

 it possesses an objectionable flavour and odour of these 

 roots. 



The exact cause of the turnipy flavour is not yet 

 understood perfectly. In some cases the milk as it is 

 drawn from the cow possesses the peculiar flavour or 

 may absorb it from the air of the cowshed where turnips 

 are stored, or used for food ; in most instances, however, 

 the trouble arises later and is a bacteriological one, 



