Page:The story of milk.djvu/120

 and loss of butter-fat in the whey. Most cheesemakers therefore prefer rennet when they can get it.

The rennet having been added, the milk is left undisturbed until a firm curd has been formed. When the curd breaks or splits sharply before the finger pushed slowly through it, it is ready to be "cut."

Cutting.—Two sets of curd knives are used, each consisting of a metal frame in which tinned steel blades are hung, in one vertically and in the other horizontally. The vertical knife is first carried slowly through the curd lengthwise and crosswise; the horizontal set of blades is then moved carefully through the length of the vat. When the cutting is over, the entire mass should be in cubes about half an inch square.

Curd knives

The whey that begins to separate out should be clear and yellow. Milky whey is a sign that the butter-fat is escaping in it; the curd has been broken up too violently. In curdling, the casein encases the butter-fat and the object of the breaking up of the curd in the vat is to expel the whey but retain the fat in the cheese.

"Cooking" the Curd.—Gentle heat is now applied to raise the temperature gradually to 98° or 100° in the course of about 30 minutes. Meanwhile the small pieces of curd are kept floating in the whey by gentle