Cheese and Casein Technology
Cheese and Casein Technology tests coagulation, whey separation, curd handling and casein recovery. The exam expects the difference between rennet coagulation, acid coagulation and the isoelectric point of casein.
Core principles
Cheese milk is standardised, pasteurised, cultured, coagulated with rennet, cut, cooked, drained, salted and pressed or ripened. Rennet clots casein by cleaving kappa-casein. Acid coagulation lowers pH to about 4.6, the isoelectric point of casein, causing precipitation. Acid casein is made by acidification; rennet casein is made by enzymatic coagulation. Cheddar is a ripened cheese; mozzarella is a stretched, plastic-curd cheese.
Worked example
1,000 kg milk contains 2.6% casein = 26 kg casein. If 90% is recovered, recovered casein = 23.4 kg. Cheddar cheese contains about 24% casein. Estimated cheese mass = 23.4 / 0.24 = 97.5 kg, or about 9.8 kg per 100 kg milk. Fat and moisture retention affect the actual yield.
Traps
Do not confuse the isoelectric point of casein with the pH of fresh milk. Do not add rennet to milk with poor calcium balance without considering calcium chloride. Cutting too hard or too soft changes curd loss and moisture. Do not wash all lactose out of a ripened cheese without considering culture and ripening.