206 . SCIENCE AND PRACTICE OF DAIRYING. 



in strength. The following facts and directions may be stated with regard 

 to the action of rennet : 



(1) The time of coagulation under like conditions of temperature, and 

 strength and amount of rennet used, is directly proportional to the quan- 

 tity of milk to be coagulated. 



(2) The time of coagulation is, under similar conditions of temperature 

 and equal quantities of milk, inversely proportional to the strength or the 

 quantity of rennet used. 



(3) The strength of rennet is, under like conditions of temperature 

 and time of coagulation, directly proportional to the quantity of milk 

 acted upon. 



On the basis of the last of these dicta, the custom of determining the 

 strength of the different kinds of rennet has been founded. These condi- 

 tions can only be regarded as holding true at temperatures between 30 

 and 40 C., and in such cases where the quantity of rennet used for 

 coagulation is not more than will effect coagulation in from five to ten 

 minutes. If the quantity of rennet be increased, and the quantity of milk 

 remain the same, the time of coagulation does not increase in the same 

 proportion as in (2) but more quickly with the increase in the quantity 

 of rennet. 



Formerly only solutions of rennet were used in practice. These 

 solutions were either made in the cheese factory daily for immediate 

 use, or were kept in very small stocks. At present, in Germany, 

 solutions of rennet are manufactured on a large scale for sale, and 

 these are almost exclusively used. Rennet is also sold in the form 

 of a powder. The introduction of this practice dates from about 

 1870, when it was introduced by the apothecary Krick of Bar-le- 

 Duc, in France, and by Dr. Christian Hansen in Copenhagen, and 

 soon also by others. 



At first the solutions were only in limited demand. They were 

 very dear, and were far from satisfactory. It was only after 

 Soxhlet had given definite instructions, based on extensive investi- 

 gations, with regard to the most economical and useful application 

 of strong rennet solutions, that commercial rennet was improved in 

 quality and reduced in price, and gradually in the course of time 

 found its way into more general use. 



The strength of the rennet preparation is best measured by 

 estimating how many cubic centimetres of a milk of ascertained 

 acidity, for example of an acidity of 7, are coagulated by one cubic 

 centimetre of rennet solution or 1 gram of rennet powder at a 



