Chapter V 



The Normal and Abnormal Microflora 

 of Butter 



THE NORMAL FLORA 



FRESH butter from unpasteurised cream will naturally contain 

 the same microorganisms as milk, and the bacterial changes which 

 take place on keeping will be the same as those which occur in 

 milk kept at the same temperature. Thus at low temperatures 

 water bacteria will tend to predominate, while at the ordinary 

 temperature the fresh butter will soon become sour owing to the 

 rapid development of lactic acid bacteria, and, in particular, 

 streptococci. Later on, lactic acid rod bacteria, yeasts and moulds 

 appear. As the moulds, which hydrolyse the fat, only appear on 

 the surface,? the keeping qualities of the butter will be greatly 

 enhanced by packing it in large casks instead of in small 

 flat slabs. Such small pieces will, unless frozen, be subject 

 in the course of a few days to the same changes, originating 

 on the surface and gradually working towards the centre, as 

 occur in a mouldy soft cheese. Butter from pasteurised ripened 

 cream will have a much simpler flora to begin with, as Strepto- 

 coccus cremoris, used in the ripening process, will generally be the 

 principal organism present. This organism, however, does not 

 seem to be capable of living long in butter, and is gradually 

 replaced by yeast, and generally also by lactic acid rod bacteria. 

 Moulds, which are an unavoidable infection from the air, gradually 

 appear on the surface. As the yeasts and bacteria only develop 

 in the small drops of water which constitute only about one-sixth 

 of the weight of the butter, it is obvious that butter will never 

 show such high bacterial counts as milk and cheese. The number 

 of microorganisms in butter will depend on the amount of nutrient 

 matter and antiseptic substances present in the water droplets ; 

 i.e., on the washing, working and addition of salt, boric acid or 

 other preservatives 1 . Properly treated butter seldom contains 



1 The preserving action of salt is more pronounced the lower the per- 

 centage of water in the butter. Thus in butter containing 2 per cent, of 

 salt, the aqueous portion will contain 12-5 per cent, of salt if the water 

 percentage is 16, but 20 per cent, if the water percentage is 10. The 

 development of microorganisms is only completely inhibited when the 



