36 Biological, Chemical and Physical Characteristics of Milk. 



Coagulation may not always appear if the milk is immediately heated to 37 deg., 

 which would indicate that some of the rennet is destroyed at 37 deg. 



If the same milk is utilized under the same experimental con- 

 ditions, it can be seen that the amount of rennet necessary for the 

 coagulation of the milk is nearly proportionately opposite to the 

 length of time necessary for the coagulation to be completed ; this 

 fact is expressed by Storch and Segelke as follows : "The product 

 from the quantity of ferment and time of coagulation is constant." 



Each kind of rennet has a certain strength which of course is changeable, and rela- 

 tive for each sample of milk. In strong dilutions of the rennet the action does not corre- 

 spond with the time rule, the time of coagulation becoming continually longer unto 

 infinity; that is, coagulation finally no longer takes place. 



The action of rennet depends on the most varied factors, 

 which may either hasten or retard its action and influence the 

 precipitation. 



Acids for instance strengthen the rennet action, likewise 

 earthy alkali salts, while alkalies, albumoses, neutral salts of high- 

 er concentrations, heating of the milk, talcum, caolin, and muci- 

 laginous substances retard the rennet action. Shaking reduces the 

 strength of the rennet if it is in solution. 



The following data are taken from a work of Smeliansky in order to show the in- 

 fluence of various additions on the rennet coagulation of cow 's milk. 

 It appears that: 



1. Heating the milk results in retarding the action. The longer the heating lasts 

 the softer and smaller are the flakes. 



2. Addition of water likewise retards the action. 



3. Mucilaginous substances retard the rennet action from taking place, and the 

 flakes formed are soft and loose. Barley water especially influences its consistence while 

 corn water principally alters the time of coagulation. 



If boiled milk is diluted with equal parts of a mucilaginous infusion and water, the 

 mucilaginous portions coagulate more quickly than the watery parts. 



4. The addition of soda solution renders the flakes soft, and retards coagulation. 

 Milk containing 0.5% of soda is entirely prevented from coagulating even after standing 

 for 24 hours. 



Four per cent of table salt renders the flakes softer. Potassium carbonate acts 

 the same as soda while the other salts respond according to their alkalinity. 



5. Milk of lime retards the action ; chlorate of lime accelerates it. If boiled milk 

 for instance coagulates after 6% hours, the time required for coagulation after the addi- 

 tion of Ca C1 2 is only 8 to 15 minutes. It causes the flakes of raw milk to become loose 

 and soft. 



According to Smeliansky, the reaction indicates the character of the coagulation, 

 and the time required for it. Sugars exert no influence. 



On the other hand Reichel-Spiro have determined a slight retarding of coagulation 

 in the presence of a high content of cane sugar. 



Cooking the milk retards the process (lowering the acidity as 

 a result of the loss of CO 2 and precipitation of lime salts, Eaud- 

 nitz). In overheated milk no coagulation or only poor coagulation 

 takes^place. The addition of water retards coagulation (Weitzel), 

 likewise physiological salt solution or whey which is free of ren- 

 net (Reichel-Spiro). Hammarsten, Lorcher, Peters, Weitzel, 

 Gerber and Eaudnitz conducted experiments relative to the action 

 of salts on coagulation, the results of which according to Eaudnitz 

 may be interpreted as follows : 



