This International Standard specifies the reference method for the determination of fat content of whey cheese. The method is not applicable to products which do not dissolve completely in ammonia solution or which contain free fatty acids in significant quantities. NOTE If the whey cheese does not dissolve completely in the ammonia or if it contains free fatty acids in significant quantities (only in exceptional cases and then noticeable by a distinct smell), the result of the determination will be too low. With such products, a method using the Weibull-Berntrop principle is suitable (see ISO 8262-3|IDF 124-3[3]).