BACTERIA IN BUTTER-MAKING 191 



selected by Conn and Esten are in fact the three chief types of 

 lactic acid bacteria. He experimented with 70 cows, and found that 

 in each cow if the milk was drawn under sterile conditions no 

 lactic acid bacteria were present in the milk, whilst in the dairy 

 experimented upon all three types were present in the air. The 

 B. acidilactici, though always present in samples of air examined, was 

 not present in excessive numbers. None of the three lactic bacteria 

 were found post mortem in the udders of two cows examined, 

 although M. varians lactis was found in the gland part of the udder. 

 Lastly, out of 300 tests of fore-milk only 2 per cent, contained the 

 normal acid bacteria, and those were contaminations from outside. 



Bacteria in Butter-making 



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 ordinarj' 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 process 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 

 constituents 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. But butter is not a good bacterial medium on 

 account of its deficiency in nitrogen. As a result of these ripen- 

 ing bacteria, the cream becomes changed and soured, and slightly 

 curdled. Thus it is rendered more fit for butter-making, and 

 gives to butter its pleasant taste and aroma. It is then churned, 

 after which bacterial action is reduced to a minimum or absent 

 altogether. Sweet-cream butter lacks the flavour of ripened or 

 sour-cream butter. The process is really fermentation, the ripen- 

 ing bacteria acting on each and all of the constituents of the 

 milk, resulting in the production of various bye-products. This 

 fermentation is a decomposition, and, just as we found when dis- 



^ Various experiments have been carried out to select good-flavouring 

 bacteria from bad-flavouring bacteria. B. subtilis and B. mesentericus 

 vulgatus have been found to be among the latter. — Centralb. f. Bakt.^ 2nd 

 Abth., 1898, pp. 730 and 759. (Eckles.) 



