ISO 663:2017 specifies a method for the determination of the insoluble impurities content of animal and vegetable fats and oils. If it is not desired to include soaps (particularly calcium soaps) or oxidized fatty acids in the insoluble impurities content, it is necessary to use a different solvent and procedure. In this case, an agreement is to be reached between the parties concerned. Milk and milk products (or fat coming from milk and milk products) are excluded from the scope of this document.