What does casein mean?
Casein is the principal protein found in milk, making up roughly four-fifths of the protein in cow's milk, with the remainder being whey protein. Chemically, it is remarkable for forming clusters called micelles, which keep it suspended in liquid milk. When milk is acidified or treated with rennet, casein coagulates into curds — the fundamental step in making nearly every kind of cheese. Beyond the kitchen, casein has long served industry: it has been used in glues (including early school glues), water-based paints prized by artists for their matte finish, and various plastics and paper coatings. In modern nutrition it is best known as a 'slow' protein, digesting gradually and therefore popular as a supplement taken before sleep by athletes seeking sustained amino-acid release. Because it is derived from animal milk, it is absent from vegan diets, and 'casein-free' labeling matters to people with certain allergies or sensitivities.
nounA slow-digesting protein that makes up about 80% of the protein in cow's milk, separated from whey during cheesemaking. It is used in cheese production and as an ingredient in adhesives, paints, plastics, and protein supplements.
- The principal protein of milk, which coagulates when acidified or treated with rennet and forms the basis of cheese.
- A commercial preparation of this protein used in adhesives, coatings, plastics, and dietary supplements.
"The painter mixed the pigments with casein to create a durable, matte finish."
"Bodybuilders often drink casein before bed because it digests slowly and feeds muscles through the night."
"Traditional woodworkers valued casein glue for its strong bond and reversible joints."
Casein is usually treated as an uncountable mass noun. The plural 'caseins' occurs mainly in biochemistry, referring to the individual protein fractions within milk.
"Milk contains several distinct caseins, including alpha-, beta-, and kappa-casein."
Casein is the reason cheese exists — and it's the same protein Elmer's Glue was once made from.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of casein
The word casein entered English from French caséine, coined in the early 19th century from Latin caseus, meaning 'cheese'. The Latin root also gives English the adjective caseous ('cheese-like') and underlies related terms such as caseinate. The ultimate origin of Latin caseus itself is uncertain, though it may be linked to a pre-Latin substrate word. Its formation follows a common pattern of the period, in which chemical substances were named with the suffix '-ine'.
Related word forms
How casein is actually used
Casein is a technical term common in nutrition science, food labeling, dairy processing, and industrial chemistry. In everyday speech it appears mainly in discussions of diet (e.g. vegan or casein-free diets) and fitness supplementation. It is uncountable in most uses; 'caseins' appears mainly in scientific writing referring to its variants (such as alpha- and beta-caseins).
Easily confused with casein
Casing is a covering or container (such as a sausage skin), while casein is a milk protein.
Creatine is a compound used in athletic supplements for energy metabolism, whereas casein is a milk-derived protein; they are often mentioned together in fitness contexts but are chemically unrelated.