NORMAL AND ABNORMAL MICROFLORA OF MILK* 75 



organism for years, the smell of the cultures remaining as strong 

 as ever. 



Milk with a Soapy Taste. As is well known, this taste arises 

 when milk is neutralised with alkalies, and is therefore produced 

 by bacteria which chiefly produce ammonia. As the neutralisa- 

 tion of the milk is counteracted by acid production, and the 

 ammonia-forming bacteria grow better at low temperatures than 

 the acid-forming bacteria, it will readily be understood that the 

 defect in question is most noticeable in cooled milk. Bacterium 

 sapolacticum, isolated by Eichholz, can grow even at 5 C. ; it is 

 a non-liquefying fluorescent organism. 



Bitter Taste in Milk. This taste nearly always occurs in milk 

 which has not been completely pasteurised, being produced by 

 the peptonising sporing bacteria. Bitter substances are nearly 

 always formed in the first stages of protein hydrolysis. The 

 defect may also be due to the cow, to certain feeding stuffs, 

 yeasts (Torula amara) and peptonising cocci, especially Strepto- 

 coccus liquefaciens. According to Weigmann, Bacterium Zopfii, 

 Bacterium lactis innocuum and aerogenes bacteria may turn milk 

 bitter. 



Metallic and Tallowy Taste in Milk. Badly-tinned vessels will 

 always impart a metallic taste to milk which is acid or fairly warm. 

 In Denmark the pasteurised separated milk is sent back warm 

 from the co-operative dairies to the farms, and in such cases it is 

 difficult to prevent the cans from being attacked to a somewhat 

 greater extent than usual, and thus giving the milk a metallic 

 taste. The metallic taste must not be confused with the tallowy 

 taste which may arise when the cream layer is exposed to direct 

 sunlight, or through the action of certain microorganisms. As the 

 metallic taste which is caused by copper is not to be distinguished 

 from the tallowy taste, it may be presumed that copper salts 

 promote by purely catalytic means the oxidation processes owing 

 to which the tallowy taste arises. According to Rosengren l , it is 

 only milk or cream which is or has been heated which gets a 

 foreign taste from the copper. The same holds good for butter 

 made from the cream. According to Storch, certain lactic acid 

 bacteria may cause a tallowy taste. Most liquefying rod bacteria 

 (the hay bacillus, etc.), may produce a sickly, tallowy taste at 

 first, but the more rapidly they peptonise the milk the sooner will 

 the taste become bitter. The author has found that some aerobic 

 non-sporing rod bacteria occasionally occurring in water are 

 generally the cause of the tallowy taste which may arise in milk 

 on long standing 2 . 



1 " Landbrugsforsogsmeddelelse," No. 197, 1920. 



2 As an instructive example it may be mentioned that a dairy which 



