CREAM 87 



ANALYSIS OF MILK PRODUCTS 



Cream. The normal constituents can be determined by 

 employing the usual methods of milk analysis after suitable 

 detection with water (vide p. 66). The amount of cream 

 used for dilution, however, should be weighed and not measured 

 volumetrically. The total solids should be determined by 

 evaporation, and Richmond recommends the addition of an 

 equal volume of alcohol to accelerate drying. Richmond also 

 finds that the total solids and fat bear the relation expressed by 

 the formula: 



Fat = 1.102 Total Solids -10.2 



Thickening agents are sometimes added to cream for the 

 purpose of increasing the viscosity and thus produce the appear- 

 ance of a cream of high fat content. The usual agents employed 

 are gelatine, starch, and saccharate of lime (viscogen). 



Small quantities of gelatine may be detected by Stokes' 

 method. 6 Mercury is dissolved in twice its weight of con- 

 centrated nitric acid (1.42) and the solution diluted with 

 twenty-five times its volume of water. To 10 c.cms. of cream 

 add an equal bulk of mercuric nitrate solution and about 20 

 c.cms. of cold water. Shake vigourously and filter after stand- 

 ing for a few minutes. Inability to obtain a clear filtrate indi- 

 cates the presence of gelatine and this may be confirmed by 

 adding an equal volume of a saturated solution of picric acid. 

 A yellow precipitate is produced by gelatine in a cold solution. 



Starch is detected by the formation of a blue colouration on 

 addition of a solution of iodine in potassium iodide. 



Saccharate of lime may be detected by the estimation of 

 either the lime in the ash or by the lactose determination. The 

 lime in normal samples averages about 22.4 per cent of the ash 

 and any perceptible increase over this amount is suspicious. 

 Similarly an abnormally high polarimeter reading, equivalent, 

 when calculated as lactose, to more than 52.5 per cent of the 

 solids not fat, should also be regarded with suspicion. 



