ESTIMATION OF WATER 207 



calcium salts with the lime present in the casein complex, and 

 casein is thrown down in a more or less pure condition. The 

 action of rennet is not so simple, for, according to Hammersten, 

 rennet converts casein into two cleavage products, paracasein and 

 whey albumin, the former in largest amount. 



In the absence of soluble calcium salts the paracasein is not 

 precipitated, but as these salts are invariably present in milk, 

 a curd is produced which is essentially different in character to 

 that produced by mineral acids or the lactic acid formed by fer- 

 mentation during the souring of milk. 



The curd produced by rennet may be regarded as crude cheese, 

 which is submitted to cutting, pressing, and other mechanical treat- 

 ment, and is finally allowed to ripen. The chemical composition 

 of cheeses varies largely, depending upon many factors, such as 

 nature of milk employed (whole milk or skim), variations in 

 pressing, salting, ripening, etc. 



197. Estimation of Water. 



About 20 grams of washed and ignited sand or 

 asbestos are placed in a porcelain basin, heated in the 

 steam oven for half an hour, cooled in the desiccator, 

 and weighed. Three to 5 grams of cheese in small 

 pieces are then weighed out into the basin, and the 

 whole heated for three hours in the steam oven. The 

 dish and its contents are cooled in a desiccator and 

 weighed, and the process repeated exactly as described 

 in the case of milk or butter (pp. 183 and 196). If the 

 heating be carried out for too long a period, there is 

 danger of loss of volatile fatty acids. A small loss of 

 ammonia invariably occurs. 



The percentage of water in cheese naturally varies 

 largely, but is generally between 26 and 46. 



Approximate Percentages of Water in Different Cheeses. 



Stilton . . . . .30 



Gruy^re ..... 35 

 Dutch ..... 37 



