🧀 Whey

Whey is the liquid left when milk is curdled and the curd is separated for cheese, cottage cheese or casein, or when yoghurt is strained. According to the Tetra Pak handbook, whey takes up 80–90% of the milk's volume and about half of its nutrients: soluble whey proteins, lactose, vitamins and minerals ¹.

Cheese whey is about 94% water, 4.5% lactose, 0.6% protein and just 0.05% fat ¹. There are two kinds: sweet whey and acid whey. Sweet whey is left after rennet cheeses and rennet casein, and its pH is 5.9–6.6. Acid whey comes from cottage cheese (pH about 5) and acid casein (4.3–4.6). According to USDA, 100 g of liquid sweet whey contains 27 kcal, 0.85 g of protein, 5.1 g of carbohydrates and 47 mg of calcium. ¹³

At the plant, whey is first strained of curd particles, then the fat and casein fines are separated and it is pasteurised ¹. It must be processed at once: bacteria grow quickly in warm whey, protein breaks down and lactic acid forms ¹.

FAO says whey is used first of all for whey cheeses and drinks, while industry obtains lactose, whey paste and whey powder ². Under the Codex standard cited by FAO, whey powder has at least 10% protein and at most 5% water, with a reference lactose content of 61% ⁴.

Membrane filtration separates the proteins. Concentrates contain 35 to 80% protein, and isolate more than 92% in dry matter ¹. Isolate is used for sports supplements, and to replace egg white in whipped products and in acidic fruit drinks ¹.

Whey or buttermilk? They are easy to mix up, but they differ by origin: whey is left when milk is curdled for cheese or cottage cheese, buttermilk when butter is churned. Whey or whey protein? Liquid whey is about 94% water with only 0.6% protein; whey protein is a concentrate (35–80% protein) or an isolate (over 92% in dry matter) filtered out of it. Whey or milk? Whey takes up 80–90% of the milk’s volume and holds about half of its nutrients, but almost no fat.

Plain liquid whey is rarely sold. On labels look for “whey”, “whey powder”, “whey protein concentrate” or “whey protein isolate”, the terms for products made from it. Powders stand in the sports-nutrition aisle, while whey drinks and whey cheeses sit in the chilled dairy section of supermarkets, health-food shops and dairies. Whey from home cheese-making has no pack to read, so chill it at once and use it quickly.

Why it matters to you. Liquid whey has almost no fat or protein, under 1 g per 100 g, so only filtration makes it "high-protein" ¹³. Lactose, however, stays in it, about 4.5%, so it is not lactose-free for people with intolerance ¹. Chill homemade whey at once and use it quickly ¹. Do not confuse it with buttermilk, which is left after churning butter.