PART III CHEESE 



INTRODUCTORY. 



IN practice cheese is made from milk, either by the action of 

 rennet or of acids. The curd which is thus obtained differs 

 in the two cases both in its chemical and in its physical 

 character. 



The theory which Hammarsten has suggested for the action 

 of rennet on milk, mention of which has already been made on 

 page 8, is ab the present time generally accepted. According 

 to it the rennet splits up the casein of the milk into two new 

 simpler substances paracasein or cheese and whey albumin. 

 Paracasein is regarded as being formerly combined with the 

 lime of the casein, and as this new compound is insoluble in 

 the milk serum, it separates out in the form of a coagulum, 

 which does not fall to the bottom. This coagulum is the crude 

 cheese, and has the property of elasticity, and the power under 

 certain conditions of shrinking together very considerably, so 

 that the whey is squeezed out. The whey albumin, which is 

 only present in small quantities compared to the paracasein, is 

 soluble, and remains in the whey. 



When acid is used for the preparation of cheese the action is 

 quite different. Generally the acid, which causes the coagula- 

 tion, is lactic acid, which is obtained when the milk, either 

 with or without the addition of sour buttermilk, becomes sour. 

 Lactic acid acts like any other acid, namely, by forming a 

 soluble calcium salt with the lime which is combined with the 

 casein, and so the latter, which is thus freed, is precipitated. 

 The curd obtained in this way is not elastic, but open and 

 sticky, and contracts less than does rennet curd. 



The crude cheese which has been obtained in one or other of 

 the above-mentioned ways, and the rennet cheeses are far and 

 away the most numerous, is then cut into small pieces by 



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