44 CLEAN MILK ' 



of skim milk, or the part of milk which forms the bulk of cheese. 

 The word caseous means cheesy. The other kind of proteid or 

 albumin remains mostly in the whey when milk is curdled. Casein 

 exists in the form of a neutral, soluble lime compound, calcium- 

 casein, while the albumin is in solution, together with the mineral 

 matter, in the water of the milk. 



In respect to curdling of milk, or coagulation of its casein, 

 one must keep in mind the following as the three most common 

 causes, (i) The most frequent — owing to souring — in which 

 germs split milk sugar or lactose into lactic acid. The lactic acid 

 breaks up the lime compound in which casein is soluble (forming 

 calcium-lactate), and so casein appears in the form of insoluble 

 curds. (2) Milk, or the casein in it, is curdled by rennet (or 

 rennin), which is formed in the stomach of man and animals. (3) 

 Germs curdle milk, also by means of a rennet-like ferment they 

 produce. The curdling of milk by rennin is often called " sweet 

 curdling." Rennin splits casein into two bodies, paracasein and 

 whey proteid. Here also the presence of lime salts in milk ( calcium 

 phosphate) is necessary for the formation of paracasein in milk by 

 rennin and its precipitation as curd. In cheese making the develop- 

 ment of lactic acid causes it to unite and form paracasein lactate. 

 Then the removal of calcium salts from paracasein by lactic acid 

 forming calcium lactate changes its physical consistency from a soft 

 •curd to a tough plastic curd which entangles most of the fat in the 

 milk while pressure squeezes out the water and soluble proteids and 

 sugar as whey. Boiling or heating milk beyond a certain point in- 

 terferes with curd formation by rennin, since it throws down the 

 lime salts. Sometimes germs cause curdling in milk by the pro- 

 duction of both acid and rennin. 



Globulin exists in but traces in ordinary milk but is present in 

 considerable amount in colostrum. It coagulates at i6/ u F. Lac- 

 talbumin, or the albumin of milk, is not curdled or coagulated by 

 the souring of milk, or by rennet, but is slightly by a temperature 



