Industrial casein, derived from skim milk, is classified based on the method of coagulation into acid casein and rennet casein. Acid casein is produced by reducing milk pH to the isoelectric point (pH 4.6), making casein insoluble. It can be obtained either by lactic acid fermentation (lactic acid casein) or by direct addition of mineral acids such as hydrochloric or sulfuric acid (mineral acid casein). Rennet casein, by contrast, is produced using the enzyme rennet (chymosin), which cleaves kappa-casein, destabilizing the micelle structure and causing coagulation.

In the mineral acid method of acid casein manufacture, fresh skim milk is preheated to 40–45°C for better coagulation. A mineral acid is then slowly added under agitation to bring the pH to 4.6, where casein curd forms. The whey, containing soluble components, is drained away, and the curd undergoes repeated washing with cold water to eliminate residual whey, lactose, and acid. This step is critical to achieve purity and storage stability. After washing, the curd is drained and mechanically pressed to lower its moisture. The pressed casein is ground into smaller particles to aid drying and then dried in a fluid bed or band dryer to a final moisture content of 8–10%. Controlled drying prevents protein damage. Finally, the dried casein is milled, sieved for uniform particle size, and packed in moisture-proof bags.

Acid casein has wide industrial applications, particularly in adhesives, binders, plastics, and paper coatings, and in foods where emulsifying and binding functions are needed, such as processed meats, coffee whiteners, and bakery products.