Answered by Shaykh Abdurrahman ibn Yusuf Mangera
Is WHEY haram? It is derived from milk and used especially by bodybuilders as the fastest absorbable protein. But in a past issue of HalalPak magazine, a certain food item was deemed haram, with the explanation, “may contain whey”.
In the name of Allah Most Pure
The reason for the problematic nature of whey is the rennet used to curdle the milk in order to produce the whey and cheese. If the rennet is halal (for instance from a halal animal, vegetable, or most microbial sources) then the whey and cheese is also halal, otherwise not.
Whey as defined by MSN Encarta: Whey, watery byproduct of the cheese making process. It is drained off after the milk has been heated and rennet (a curdling agent) added to induce coagulation. In Scandinavia, especially Norway, whey is turned into cheese, mysost and gjetost (from goat’s whey). The flavor of whey cheese is sweet from added brown sugar. When whey is heated under controlled conditions, the protein molecules bond in a process called polymerization to form an edible film. Researchers have been looking at applications for this film in the food preservation and sports nutrition industries.
Whey: A watery part of the milk, milk serum, and it is the liquid that remains after the curd and the cream are removed from the coagulation of the casein of milk. Curdling of milk for cheese preparation takes place with the use of the enzyme rennet. As for the cheese, the enzyme rennet used to produce the cheese may be from animal origin and from pig source.
Rennet is used to curd the milk. Whey should be avoided because the rennet used to curd the milk could be from a haram or non-Zabihah animal.
And Allah knows best.