Comparison of rennet gelation using raw and reconstituted skim milk

The gelation properties of raw skim milk were compared with milk reconstituted from low-heat skim milk powder. Coagulation of reconstituted milk, as monitored by capillary viscometry, was slower than that of raw milk, but increased markedly with increased reconstitution time. This was attributed to re-equilibration of calcium from the micelles to the serum. Freshly reconstituted milk supplemented with calcium confirmed this suggestion. The results emphasise the importance of calcium being present in the serum for coagulation of renneted micelles. Gel strength was also improved by increasing reconstitution time. However, gels made from raw milk were significantly stronger than those made from reconstituted milk, even when supplemented with 3 mm calcium. The decreased gel strength from reconstituted milk was attributed to a general increase in casein micelle size that occurs during powder manufacture and is not reversed upon reconstitution.