You can make cottage cheese with rennet (a substance that causes milk to curdle) for large-curd sweet cheese or without rennet for old-fashioned, small-curd tart cheese. To prevent the curds from getting tough and rubbery, it’s essential to control the temperature rise, limiting it to 5 degrees or less during each 5-minute period of cooking.
For this purpose you’ll need an accurate, easy-to-read thermometer and two large pans in a double boiler arrangement. The more milk you work with, the easier it is to raise the temperature gradually. For additional information about basic steps and ingredients, see Cheesemaking. Large-curd sweet cottage cheese Heat 2 gallons pasteurized skim milk or reconstituted nonfat dry milk to 90F; add to it 1/2 cup unpasteurized buttermilk. Crush 1/4 tablet rennet and dissolve it in 1/4 cup cool water. Mix well into milk. Keep the temperature at about 90°F but no higher for 5 hours, or until milk coagulates and breaks cleanly away from a spoon or finger dipped into curds.
Cut curds into 1/2-inch cubes and heat curds and whey (the liquid residue) very slowly to between 110F and 115F; maintain this temperature for about 1/2 hour, or until a lump of curd holds together when pressed gently between thumb and forefinger.
Strain through cheesecloth and hang to drain until the dripping becomes very slow. Immerse the bag of curds in cold water and stir the cheese gently with a spoon to rinse curds in center. Drain again, then gradually mix in 5 to 6 teaspoons salt. If you like a moist cheese, add a little cream. Small-curd cottage cheese Heat 2 gallons pasteurized skim milk or reconstituted nonfat dry milk to 72F; stir in thoroughly 1/4 cup unpasteurized buttermilk. Cover pan with plastic wrap; leave in a warm place from 16 to 24 hours, or until milk sets or coagulates.
Cut the curds into 1/4-inch cubes. Cook, drain, and salt as for large-curd cottage cheese.