ACID CURDLING AND KENNET CURDLING. 241 



is in this case split up into two portions differing greatly in 

 amount, viz., lac to -protein, small in quantity, soluble, and re- 

 maining in the whey, and the insoluble paracasein. The latter, 

 therefore, forms the chief constituent of the coagulum separated 

 ("set") in cheese-making by the aid of rennet, and known as 

 rennet curd (Ger. Bructi), or crude cheese. 



Casein, or paracasein, though the sole nitrogenous constituent 

 of the coagulum produced in any of these methods, is, however, 

 by no means its sole component, a number of other substances 

 being precipitated and carried down at the same time. If whole 

 milk i.e. unskimmed milk is set for cheese, almost the whole 

 of the fat will be found in the curd, which will then subsequently 

 produce rich cheese skim-cheese being the result in the converse 

 case. Along with the fat, the calcium phosphate contained (in 

 suspension) in the milk will also be thrown down only in the case 

 of rennet curd, not in the curd produced by acidification. 



Not only are fat and (in this instance) calcium phosphate 

 carried down by the coagulum, but also a large part of the 

 organisms present in the milk will be found in the fresh curd, so 

 that the latter is relatively as rich in organisms as the milk from 

 which it was precipitated. Here, again, a considerable difference, 

 from a biological point of view, exists between the two classes of 

 curd, and exercises a decisive influence on their subsequent career. 

 The flora of the rennet curd from sweet (i.e. almost neutral) milk 

 is much more diversified than that of acid curd. The latter, 

 having been thrown down from a sour milk in a state of vigorous 

 lactic fermentation, consequently contains only a limited number 

 of species, and these endowed with a particular fermentative 

 power. 



Acid curd differs, therefore, from rennet, both in the method 

 of production and also in composition. Being devoid of flavour, 

 both kinds are, however, unsuitable for food; their conversion 

 into a form in which they both stimulate the appetite and are also 

 themselves more readily digestible, is the task of the cheesemaker's 

 art, fuller particulars of which, from the bacteriological point of 

 view, will be found in Chapter xxxi. 



145. Characteristics and Activity of Lab, 



If the enzyme in question were exclusively a metabolic product 

 of the animal body, the foregoing details would suffice. However, 

 since it is excreted by many fungi as well, a few additional par- 

 ticulars will not be out of place in a work dealing with technical 

 mycology. 



"When and in what manner the attention of mankind was 

 first drawn to this enzyme cannot be determined, since even the 

 oldest authorities, e.g. the Bible, speak of its employment as an 

 ancient practice. Its method of action, however, was unknown 



VOL. I. Q 



