This part of ISO 15788 specifies a method for the determination of steradienes, especially stigmastadienes. Steradienes are formed by dehydration of sterols during bleaching and also partially during steam washing and deodorization. The method is also suitable as a screening method to detect the presence of refined vegetable oils in virgin oils such as virgin olive oil. NOTE ISO 15788-1 is the reference method for the determination of stigmastadienes in vegetable oils whilst this part of ISO 15788 can be used as a rapid screening method. In view of the precision of this method (see Annex A), samples of virgin olive oils close to the limit adopted by international regulations (IOOC, EC) can be verified by the GLC method given in ISO 15788-1.