68 MILK ANALYSIS 



genuine cheeses, the proportion of proteic, amidic, and ammo- 

 niacal nitrogen is of value. 



Care should be taken to select for analysis a sample which 

 represents the average composition of the entire cheese. 



The following methods for the determination of water, fat, 

 ash, total nitrogen, and acidity have been adopted by the A. O. 

 A. C.: 



Sampling. When the cheese can be cut, a narrow wedge- 

 shaped segment, reaching from the outer edge to the center 

 of the cheese, is taken. This is to be cut into strips and passed 

 through a sausage-grinding machine three times. When the 

 cheese cannot be cut, samples are taken by a cheese trier. If 

 only one plug can be obtained, this should be perpendicular 

 to the surface, at a point one- third of the distance from the edge 

 to the center of the cheese. The plug should reach entirely 

 through, or only half-way through, the cheese. When possible, 

 draw three plugs one from the center, one from a point near 

 the outer edge, and one from a point half-way between the 

 other two. For inspection purposes, the rind may be rejected; 

 but for investigations requiring the absolute amount of fat in 

 the cheese, the rind is included in the sample. It is preferable 

 to grind the plugs in a sausage machine, but when this is not 

 done, they should be cut very fine and carefully mixed. 



Water. Between 2 and 5 grams of the sample should be 

 placed in a weighed platinum or porcelain dish which con- 

 tains a small amount of material, such as freshly ignited asbestos 

 or sand, to absorb the fat that may run out. This is then heated 

 in a water-oven for 10 hours and weighed; the loss in weight 

 is considered as water. If preferred, the dish may be placed 

 in a desiccator over concentrated sulfuric acid and dried to con- 

 stant weight, but this may require many days. The acid 

 should be renewed when the cheese has become nearly dry. 



Fat. The extraction- tube described on page 14 is prepared 

 as follows: Cover the perforations in the bottom of the tube 



