Effect of Milk Quality and Low Temperature Storage on Cheese Yield—A Summation

Abstract

The effect of low temperature storage and milk quality on cheese yield was investigated. Raw milk was stored at 5, 7.5, and 10°C; grade A milk was stored for 6 to 12 d and manufacturing grade milk for up to 6 d. At 1-d (manufacturing grade) and 2-d (grade A) intervals, aliquots from each treatment were pasteurized and manufactured into cheese, and the resulting yield was compared with that obtained on d 0 for manufacturing and grade A milks, respectively. Each treatment was terminated when stored milk coagulated when pasteurized. Increase in total bacterial count ranged from one log cycle for high count manufacturing grade milk to more than three log cycles for low count grade A milk. Similar changes were observed for proteolytic and psychrotrophic populations. As stationary populations were approached, essentially all organisms were psychrotrophic, and most were proteolytic and lipolytic. Cheese yield was affected by initial psychrotrophic populations and length of time raw milk was stored. Recovery of cheese solids decreased by approximately .5% for manufacturing grade milk per day of storage up to 4 d. Further storage increased the loss of cheese solids, and loss of cheese yield correlated with increase in bacterial population. Yield loss appeared to be due to exocellular enzymes causing breakdown of proteins and fats. Protein degradation was accompanied by increased moisture in the curd. Cheese quality decreased as psychrotrophic populations increased. After pasteurization high count stored raw milk contained enough psychrotrophs to dominate the aging process, producing gassy unclean cheese. Stored milk cheese had a weak body with bitter flavors typical of that produced by heat-stable proteolytic enzymes.