The reference method of analysis figuring in the Annex shall be applied to ensure that cheese which must be made exclusively from ewes' milk, goats' milk or buffalos' milk or from a mixture of ewes', goats' and buffalos' milk does not in fact contain cows' milk casein. Cows' milk casein shall be held to be present, if the apparent cows' milk casein content of the sample to be analysed is equal to or higher than the content of the reference sample containing 1 % cows' milk described in the Annex.