Dairy processing and cold storage affect the milk coagulation properties in relation to cheese production

The development of coagulation properties during cold storage of raw milks categorized as good or poorly coagulating is largely unknown. This was studied in the present investigation at individual cow's milk level in addition to elucidating the impact of cheesemaking processing steps on the resulting coagulation properties of silo tank cheesemilk. Rennet coagulation time (RCT), curd firming rate (CFR) and gel firmness (G'max); Ca, P and Mg distribution; pH; and casein micelle size of raw skim milk from individual cows classified as "good" or "poor" in coagulation properties were investigated over 72 h storage at 4 A degrees C. For the cheesemilk, the impact of overnight cold storage, thermization and standardization, pasteurization, and acidification to either pH 6.45 or 6.30 on the coagulation properties were studied. After 24 h of cold storage, RCT of both good and poorly coagulating milks was significantly prolonged though recovering somewhat after prolonged storage for good coagulating samples. In contrast, G'max was significantly reduced after 72 h of cold storage for good coagulating milk. Both total and colloidal Ca were higher in good compared with poorly coagulating milk, while mineral distribution and milk pH did not change during storage. For cheesemilk, up to 14 h, cold storage did not impair coagulation properties significantly, which was markedly improved by acidification. The study shows that rheological parameters of good and poorly coagulating milks are impacted differently by the cold storage. Conversely, cheesemilk coagulation properties were not impaired by the studied cheesemaking processing steps and, further, were enhanced by acidification steps.