This International Standard specifies the determination of the degree of isomerization of diacylglycerols in vegetable fats and oils. 1,2-diacylglycerols are transformed to the more stable 1,3-isomers during storage or due to acidic catalyzed reaction. The mass fraction of 1,2-diacylglycerols can be used as a quality criterion for vegetable fats and oils. The absolute content of diacylglycerol can be used as authenticity criterion for vegetable fats and oils. Milk and milk products (or fat coming from milk and milk products) are excluded from the scope of this document.