Effects of Time and Temperature of Holding Milk Heat-Treated at Various Temperatures upon Its Subsequent Coagulation by Rennet

Open Access
Publisher Website
Google Scholar
Abstract
During the entire study both the holding method and the flash pasteuriza- tion process were used. With the first method two liters of fresh skimmilk were placed in a loosely stoppered flask and rapidly heated in a water bath to 65 ° C., 75 ° C. or 85 ° C. and maintained at the respective temperature for 30 minutes. A portion of each lot of milk was then kept at the heating tem- perature while two other portions were removed and rapidly cooled, one to 35 ° C. and the other to 5 ° C., each being held at that temperature. Two 50 ml. samples were immediately removed from that portion cooled to 35 ° C. and rennet added for coagulation. Duplicate 50 ml. samples from each of the above portions were removed and rennet added at various intervals after the initial heating period. All samples were coagulated at 35 ° C. in the electrically heated and controlled water bath previously (1) described. At least two complete determinations were made for each temperature that was studied. Each sample was placed in a coagulation tube 10 minutes before addition of the rennet in order to adjust itself to the temperature of the bath. One ml. of a 3 per cent rennet solution was added to each 50 ml. of milk, a stop- watch started and the milk stirred for 30 seconds. After an appropriate interval the screw clamp closing the bottom of the coagulation tube was re-