MICROFLORA OF BUTTER 121 



more than a few million bacteria per cubic centimetre. In butter 

 from unripened cream, the bacterial count increases during the 

 first few days 1 , after which it decreases. In butter from ripened 

 cream the count is highest when the butter is freshly made (ten 

 to twenty million lactic acid bacteria per cubic centimetre), and 

 decreases steadily in the course of a few weeks to a few 'hundred 

 thousand, and sometimes even to as low a figure as a few thousand, 

 the reason being that the original lactic acid bacteria die off at a 

 quicker rate than their successors develop, for the available 

 nutrient matter, especially lactose, is continually falling off. In 

 cases where fat hydrolysis is taking place, this source of carbon 

 will be replaced by glycerine, and the lactic acid bacteria will then 

 again fare better. 



On keeping for any length of time, butter acquires a stronger 

 flavour, and it becomes rancid quicker than other fatty materials 

 on account of the large amounts of water and nutrient substances 

 which it contains. Before the introduction of margarine, com- 

 pound and other substitutes, it was a common custom in Central 

 Europe to preserve the butter fat by melting and separating off 

 the other constituents ; the pure butter fat kept good if preserved 

 in well closed stone jars in a cool place. 



Dudaux 2 was the first to study the changes which take place in 

 butter on keeping. He found that direct sunlight promoted the 

 action of atmospheric oxygen, i.e., its function was similar to 

 that of the oxidases, causing oxygen to combine with the con- 

 stituents of the butter-fat, especially the olein. Dudaux also 

 found that butter was spoiled by various moulds to which he 

 ascribed an action similar to that of sunlight in oxidising the fat. 

 The author's investigations 3 show that there is an important 

 difference between the action of sunlight and that of micro- 

 organisms. While fats are principally oxidised under the action of 

 sunlight, the iodine value being reduced, they are hydrolysed by the 

 microorganisms into fatty acids and glycerine, the acid value being 

 increased. Oxidation causes changes in taste which are much 

 more undesirable than those caused by hydrolysis ; if butter is 



concentration of salt reaches 25 per cent., e.g., with 13 per cent, of water 

 and 3*3 per cent, of salt (tinned butter). If permissible by law, it is specially 

 recommended to add 0-75 per cent, of benzole acid, or 2 per cent, of sodium 

 benzoate, or a mixture of O5 per cent, of benzole acid and 0'5 per cent, of 

 sodium benzoate. As benzole acid is a physiological product (it is trans- 

 formed to hippuric acid), it may be regarded as one of the less objectionable 

 preservatives. 



1 The highest count ever obtained by the author from butter made from 

 unripened cream was 59 millions per cubic centimetre. 

 " Ls lait," Paris, 1894. 



3 " Studien iiber das Kanzigwerden der Butter" ( " Centralblatt f. 

 Bakt.," 2 Abt., 1902, Bd. VIII., p. 11). References to earlier literature given 

 here. 



