Variation in Coagulation Properties of Milk from Individual Cows

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Abstract
Milk samples from 50 Holstein cows were tested monthly for 10 mo. for total protein, casein, fat, somatic cells and pH. A Formagraph was used to measure chymosin coagulation properties. Significant variations in coagulation time and curd firmness were observed in relation to period of lactation, individual cows and milk pH. A high negative correlation coefficient (-0.86) was observed between coagulation time and curd firmness measured 30 min after addition of chymosin. The mean coagulation time generally increased as lactation progressed and milk yield decreased. Curd firmness was generally greatest in midlactation samples. Milk from 38% of the cows did not coagulate in 30 min 1 mo. prior to their dry periods. The frequency of failure to coagulate was 68% in winter and 32% in fall. Milk pH was the most significant factor that affected coagulation time and curd firmness. Simulated cheese making procedures were used to estimate recovery of fat and protein in curd. Curd yield calculated from the recovery data ranged from 5.4 to 14% with a mean of 9.2%.