Whey

Whey is the watery liquid left behind when milk is curdled and strained during cheesemaking, carrying much of the milk's lactose, whey proteins and minerals while the solid curds are pressed into cheese. Rather than being discarded, whey is used to make its own cheeses, such as Italian ricotta and Norwegian brunost, and is dried and concentrated into whey protein powders widely sold as a fitness and nutrition supplement. Historically it was also fed to livestock or used as a base for traditional fermented beverages and in baking, and industrially it remains a major byproduct stream of the global cheese industry.