312 SCIENCE AND PRACTICE OF CHEESE-MAKING 



the case of one individual (No. 14), the variations 

 were from 4 minutes and 45 seconds to 50 minutes. 

 A study of the ordinary composition of the milk gave 

 no clue to the cause of such differences. The specific 

 causes are not yet understood, but are probably related 

 to the calcium salts in milk and their solubility. 



PEPSIN-ENZYM 



The chief enzym of the gastric juice in the stomach 

 of man is known as pepsin. The same enzym is also 

 present in the stomach of many animals. A prepara- 

 tion made from the stomachs of sheep is on the 

 market, which may be successfully used as a sub- 

 stitute for rennet-extract in cheese-making. This 

 has the property of both coagulating and digesting 

 milk-casein. The pepsin most experimented with 

 has been the scale pepsin of Armour & Co. This 

 pepsin does not coagulate very sweet milk as read- 

 ily as rennet-extract, but in milk having an acidity 

 of 0.20 per cent, it acts just as Well, when used in 

 the proportion of 5 grams for 1,000 pounds of 

 milk. The pepsin is dissolved in any convenient 

 amount of water before addition to milk. The 

 solution should be prepared fresh for each day's use. 

 The complete identity of rennet-enzym and pepsin is 

 not fully settled. Assuming that the coagulating 

 effect of these preparations is due to one enzym 

 (rennin) and the digesting effect to another (pepsin), 

 the various preparations differ in respect to the 

 amounts of these two enzyms which they contain. 

 Rennet-extracts contain more rennin and less pepsin, 

 while the commercial preparations made from the 

 stomachs of pigs and sheep appear to contain more 

 pepsin and less rennin. 



