126 DAIRY BACTERIOLOGY 



with the naked eye, but most of the other moulds form green, 

 brown or black spots. As has already been mentioned, butter from 

 sweet cream may be coloured red by certain torulse, which in 

 symbiosis with lactic acid bacteria hydrolyse fat and also give an 

 oily taste in butter. Actinomyces chromogena turns butter brown 

 and gives it an unpleasant earthy smell. Among the secondary 

 defects of taste, the sour cheesy taste deserves special considera- 

 tion. The acid is chiefly due to lactic acid rod bacteria, so that 

 the defect is particularly likely to arise when the butter has not 

 been properly freed from buttermilk or when it contains lumps of 

 casein in which these cheese bacteria may initiate a cheese- 

 ripening process. The defect, however, only attains its worst 

 form when a symbiosis with yeast gives rise to fat hydrolysis 1 . 

 Certain yeasts may produce a fishy or train-oil taste. In marshy 

 districts or where the land is occasionally inundated by sea or 

 brackish water, this defect may appear in fresh butter, and is 

 then due to the grass or small crabs which- are found in great 

 numbers in the grass. Certain bacteria are also said to be able to 

 produce a fishy taste by forming trimethylamine from lecithin 2 . 

 Some of the defects which may appear in butter after keeping for 

 any length of time are of a purely chemical nature, like the oxida- 

 tion process discussed above, and their appearance may be 

 accelerated by iron and possibly other salts. It is therefore of 

 importance that the salt used in butter should be chemically pure 3 . 

 It has been said that dairy salt may contain fat hydrolysing 

 bacteria 4 . Fresh pure salt is of course sterile, but when kept in 

 the dairy, numerous organisms (thousands per gram) may collect 

 on its surface, and Weigmann has therefore proposed to dry the 

 salt in an air oven at 100 C. before use. 



As butter defects which are apparently of the same nature may 

 arise in different ways, and conversely, as is often seen to be the 

 case in butter grading, the same defect may pass under different 

 names, it is hardly possible in the present state of our knowledge 

 to go into further detail as regards the secondary defects. As, 

 moreover, most of the defects sooner or later pass into the stage 



1 The author was the first to show that the ability of certain yeasts to 

 hydrolyse fat is promoted in the presence of lactic acid bacteria : " Bak- 

 teriologisehe Studien iiber die danische Butter" (" Centralblatt f. Bakt.," 

 2 Abt., 1911, Bd. XXIX., p. 610). This was later confirmed by Sandelin : 

 "Die Hefen der Butter," Helsingfors, 1919. 



2 Thus, Cusick (" Journal of Dairy Science," 1920, Vol. III., p. 194) is of 

 the opinion that this defect can be produced by Bad. ichthyosmius, a motile 

 Gram-negative rod showing dirty white surface growth, peptonising milk 

 while producing slight amounts of acid, and producing gas from cane sugar, 

 but not from lactose. 



3 Rogers, Berg and Potteiger, U.S. Dept. of Agric., Bureau of Anim. Ind., 

 1913, Bull. 162. 



4 Wolff, " Milchzeitung," 1914, p. 545. 



