39 



per (oiit of acid or when the milk coajjiilates by the Monrad test in 

 lorty-five to sixt}" seconds or by the Marschall test in two and one- 

 half spaces. Milk containinjj; as much as 0.2 per cent of lactic acid 

 when delivered at the factory is overripe and liable to cause trouble 

 (references No. 3, p. 69, and No. 8, p. 48). 



7. Adding color. — When coloring matter is used, it should be added 

 just before the rennet is, being diluted before addition and thoroughly 

 mixed into the mass of milk (reference No. 8, p. 52). The amount 

 used depends upon the special demand of the market. 



8. Preparation and addition of rennet. — Adding rennet is commonly 

 known as "setting milk with rennet." The milk is heated gradually 

 to 84° to 86° F., with constant stirnng and tested for ripeness. If ripe 

 enough, rennet is added at once. If not ripe enough, it is allowed to 

 stand until it gives the right test, a starter being used or not, as circum- 

 stances require. When the milk is ripe enough, the rennet extract is 

 added. In this connection three points must be considered — (1) tem- 

 perature of milk, (2) amount of rennet added, and (3) method of 

 adding extract. 



(a) Temperature of milk. Different makers use for setting milk 

 different tempen.tures varying from 82° to 86° F. The higher tem- 

 perature saves time by hastening ripening, especially when no starter 

 is used. At temperatures much above 86° F. the curd hardens too 

 quickly to handle conveniently, and there is danger later of loss of 

 fat (references No. 3, p. 70, and No. 8, p. 52). 



(b) Amount of rennet extract to use. This will depend on the 

 strength of the extract, other things being equal. ITse enough to 

 coagulate the milk in fifteen to twent}" minutes for a quick-curmg 

 cheese and in thirty to forty minutes for a slow-curing cheese. The 

 extract commonly used is added at the rate of 2^ to 5 ounces for 

 1 ,000 pounds of milk. 



(c) Method of adding rennet extract. Before being added to milk 

 the rennet should be diluted wdth twenty to forty times its volume of 

 M^ater to prevent uneven action in the milk. The milk should be 

 thoroughly stirred just before the rennet is added. Then after the 

 addition of the rennet the milk is at once stirred again gently, but 

 thoroughly, and continued for some minutes. Then the surface is 

 stirred quietly to keep cream from rising, but is stopped before there is 

 any sign of coagulation. The surface is then covered with cloth to 

 hold temperature and the milk kept undisturbed until coagulation is 

 complete (references No. 3. p. 71, and No. 8, p. 53). 



[Suggestions to lecturer: Each student should receive special prac- 

 tice under supervision in each of the manipulations described. Prac- 

 tice in ripening milk can at first be obtained with snu 11 amounts of 

 milk. The preparation and use of starters must receive most careful 

 attention in practice. In working with larger quantities of milk the 



