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Effect of pH at Cutting and during Cooking on Cottage Cheese^1,2,

Food Research Institute, Research Branch, Agriculture Canada, Ottawa, Ontario K1A 0C6

ABSTRACT

In two experiments, cottage cheese was 1) cut at pH 4.9, 4.8, 4.7, and 4.6 and pH of whey adjusted with sodium hydroxide or lactic acid to 4.5 during the latter stages of relatively slow cooking to 60°C, and 2) cut at pH 4.9 and pH of the whey similarly adjusted to 4.8, 4.7, 4.6, or 4.5 during cooking. Firmness and total solids of curd increased during cooking from 46.1 to 60°C in all treatments.

Cutting at lower pH resulted in markedly less firmness and total solids and in less matting, but fines in whey were higher. The relation between total solids and firmness of washed curd taken during cooking was a single curved line.

Cooking at lower pH resulted in lower total solids in the curd in the four treatments. However, lower pH resulted in firmer washed curd after cooking at 46.1°C but softer curd after 60°C. Relations between total solids and firmness during cooking were four parallel lines for curd cooked at pH 4.8, 4.7, 4.6, and 4.5; curd cooked at higher pH had higher total solids at the same firmness. A decrease of pH of .1 during cooking resulted in decrease of total solids of approximately .5% at the same firmness, an important practical consideration in yield of cheese.

Cultures and total solids of milk affected pH change during cooking. The drop of pH from 4.8 during 75 min ranged from .13 to .32 with different cultures. In skim milk reconstituted to 6, 8, 9, 10, and 12% total solids, drops of pH from 4.8 during 75 min were .31, .25, .22, .20, and .16 pH units.

¹ Contribution No. 571 from the Food Research Institute.

² A brief summary of the paper appeared as a short communication to the XVII International Dairy Congress in Melbourne, 1970 (5).