WPC remain soluble after adding rennet, or when the pH of milk is lowered to 4.6. They are found in whey hence their names: Soluble, serum, or whey proteins. They include β-lactoglobulin,  α-lactalbumin, albumin serum and immunoglobulins. The β-lactoglobulin is quantitatively the most important serum protein.

Their protein content vary from 15% to 80%. They are made from de-salted and lactose-free whey, to varying degrees, generally by using whey ultra-filtration.

Protein concentration of WPC can be increased by the use of diafiltration. Drying is usually done by spray (spray drying).