Macro-casein micelles were observed in the separator sludge, preparated from raw milk, using electron microscope. The size of these casein micelles were about 300 mµ to 1000 mµ in diameter.
The constituents of separator sludge were 76.19% water, 17.63% protein (12.86% casein and 4.77% non casein protein), 2.57% ash and 3.61% other materials. This separator sludge contained 35.73 mg Ca, 4.79 mg Mg and 20.64 mg P per 1 gram of the protein. Casein was the principal component in the protein of this separator sludge or in the sludge itself except water.
Casein must exist in raw milk as micelles of various size distribution and only large size micelle removed to separator sludge by centrifugation of cream separator.