This International Standard specifies a method of determining the insolubility index, as a means of assessing the solubility, of dried whole milk, dried partly skimmed milk and dried skimmed milk, whether non-instant or instant. NOTE These milks are defined in Reference [7] as “whole milk powder”, “partly skimmed milk powder” and “skimmed milk powder”, respectively. The method is also applicable to dried whey, dried buttermilk and dried milk-based baby food, as well as to any of the dried products listed in which milk fat has been replaced by another fat, or which has been rollerdried instead of spray-dried.