32 THE BOOK OF CHEESE 



spoken of as " rennets " in the trade. Such old rennets 

 may be seen to-day hanging from the rafters of some of 

 the older cheese factories. When wanted for use, rennets 

 are placed in oak barrels and covered with water. Before 

 placing them in the barrel, they are cut open so that the 

 water may have easy access. Salt is usually added to 

 the water at the rate of 3 to 5 per cent. They are stirred 

 and pounded in this solution from five to seven days. 

 At the end of this time, they are wrung through a clothes- 

 wringer to remove the liquid. The rennets are put back 

 into a fresh solution of salt and water, the object being 

 to obtain all the digestive juices possible. They are 

 usually soaked from four to six weeks. At the end of 

 this time, most of the digestive juices will have been re- 

 moved. The liquid portion is passed through a filter 

 made of straw, charcoal and sand. When clean, an excess 

 of salt is added to preserve it. 



Such extracts cannot be sterilized by heat because 

 the necessary temperature would destroy the enzyme. 

 Effective disinfectants cannot be used in food products. 

 The extract, therefore, should be kept cool to retard bac- 

 terial growth. The extract is kept in wooden barrels, 

 stone jugs or yellow glass bottles to protect it from light, 

 which is able to destroy its activity. Rennet extract 

 should be clear, with a clean salty taste and a distinct 

 rennet flavor. There should be no cloudy appearance 

 and no muddy sediment in properly preserved rennet. 

 Rennet extract is on the market in the form of a liquid 

 and a powder, the former being much more common. 

 The commercial forms of rennet have the advantage in 

 the skill used in their preparation and standardization. 

 The combined product from large numbers of stomachs 

 may not be as effective a preparation as the most skillfully 



