This International Standard specifies a reference method for the determination of milk fat purity using gas chromatographic analysis of triglycerides. Both vegetable fats and animal fats such as beef tallow and lard can be detected. By using defined triglyceride equations, the integrity of milk fat is determined. Basically, the method applies to bulk milk, or products made thereof, irrespective of feeding, breed or lactation conditions. In particular, the method is applicable to fat extracted from milk products purporting to contain pure milk fat with unchanged composition, such as butter, cream, milk, and milk powder. However, under the circumstances listed hereafter, a false positive result can be obtained. Hence, the method is not applicable to milk fat: a) obtained from bovine milk other than cow's milk; b) obtained from single cows; c) obtained from cows which received an exceptionally high feeding of pure vegetable oils such as rapeseed oil; d) obtained from colostrum; e) subjected to technological treatment such as removal of cholesterol or fractionation; f) obtained from skim milk or buttermilk; g) extracted by using the Gerber, Weibull-Berntrop or Schmid-Bondzynski-Ratzlaff methods, or that has been isolated using detergents (e.g. the Bureau of Dairy Industries method). With the extraction methods specified in g), substantial quantities of partial glycerides or phospholipids can pass into the fat phase. Consequently, the scope of this International Standard excludes certain products and particularly cheese, whose ripening process can also affect the fat composition to such a degree that a false positive result is obtained. NOTE 1 In nature, butyric (n-butanoic) acid (C4) occurs exclusively in milk fat and enables quantitative estimations of low to moderate amounts of milk fat in vegetable and animal fats to be made. However, due to the large variation of C4, whose approximate content ranges from 3,1 % mass fraction to 3,8 % mass fraction, it is difficult to provide qualitative and quantitative information for foreign fat to pure milk fat ratios of up to 20 % mass fraction (see Reference [11]). NOTE 2 In practice, quantitative results cannot be derived from the sterol content of vegetable fats, because they depend on production and processing conditions. Furthermore, the qualitative determination of foreign fat using sterols is ambiguous.