458 Conditions Affecting Butter-Fat. 



This last observation is of importance in view of the com- 

 pulsory use of sesame oil in the manufacture of margarine in 

 Germany and Belgium. As sesame oil may be readily detected 

 by comparatively simple tests, the presence of such margarine in 

 butter may be easily recognised. 



The flavour of butter, upon which its commercial value so 

 largely depends, is not directly connected with the nature or 

 amount of its constituent glycerides. Flavour would appear to 

 be the result of the action of bacteria, and the extent and character 

 of the flavour would seem to be materially affected by the con- 

 ditions under which the micro-organisms exist. That the 

 chemical nature of the fats in the milk — that is, the nature and 

 relative proportion of the fatty acids — has little or nothing to do 

 with the flavour, would seem to be proved by the fact that the 

 same cream will yield butters of very different flavour, depending 

 on the manner in which the cream is raised. The butter from 

 separated cream is, as a rule, markedly different in flavour from 

 that made from shallow pan cream. 



If butter fat be sealed up and kept in a cold, dark place, it 

 will retain its normal character and appearance for many months, 

 but if kept in a warm locality, with free exposure to air and 

 light, it will very speedily undergo chemical and physical changes 

 and become, as we say, rancid. 



According to Browne (J. Amer. Chem. Soc, 1899, 976), by 

 the term "rancidity" is not simply meant, as is generally sup- 

 posed, a development of free acid — though this is usually an 

 attendant circumstance — but simply oxidation, and in the early 

 stages of the process butter-fat may lose its characteristic colour 

 and smell, and develop an abnormal taste without showing an 

 excessive degree of acidity. 



That rancidity in butter is primarily the result of the activity 

 of bacteria is, no doubt, partly true of whole butter, with its 

 lactose, casein, and other constituents to serve as bacterial food, 

 but it is certainly not the case with pure butter-fat, which is 

 unable to support micro-organic life. The independent researches 

 of Duclaux and Rilsert prove that bacteria cannot thrive in a 

 medium of pure fat, and that all changes which take place in 

 fats on keeping are wholly the result of an oxidation, conditioned 

 to a great extent by exposure to light. 



