86 DAIRY ANALYSIS 



the fat and specific gravity as previously described ; 

 to 100 c.c. of milk add o.oi gramme of rennet powder, 

 and keep at 42 C. till curdled ; cut up the curd and 

 allow it to settle, and strain off the whey through muslin ; 

 cool the whey to 15.5 C. and estimate the specific 

 gravity and the fat as before. 



Add the degrees of gravity and the percentage of 

 fat of the milk and subtract the sum of the degrees of 

 gravity and the percentage of fat of the whey ; the 

 difference divided by 3.5 will give the percentage of 

 dry curd available for cheese -making. 



In practice the whey obtained during cheese-making 

 may bs tested instead of a separate preparation of whey 

 being made ; the sample for testing should, however, 

 be removed as early as possible. 



The difference in acidity (see p. 15) between the 

 milk and the whey divided by 3.5 will also give a rough 

 estimation: of dry curd. 



This will give an idea of the value of milk for cheese - 

 making. The percentage of dry curd plus the per- 

 centage of fat less 0.25 divided by 0.055 will gi ye the 

 number of pounds of cheese per 100 gallons of milk.* 



A fermentation test is useful ; plug a number of 

 clean test-tubes with cotton-wool, and sterilise by 

 heating to 150 C. in an air-bath for* half an hour. 

 Place 10 c.c. of the milk to be examined in one of 

 these, and keep it at blood-heat for eighteen hours ; if 

 the precipitated curd is distended by bubbles of gas the 

 milk will not make good cheese. 



The acidity of the milk before renneting should be 

 estimated (p. 15), and that of the whey after the curd 

 is cut, and the whey running from the curd at intervals. 

 As an example of the use of the acidity test, in Cheddar 

 cheese-making the best acidity of the milk for renneting 

 is 22-24 ; the acidity of the whey is less than this, 

 but constantly increases ; the whey should be drawn 



* The factor 0.055 w ^ require modification according to the 

 kind of cheese made ; it applies fairly well to Cheddar and Cheshire 

 cheese. 



