FOODS 95 



appearance is got. No selenite plate should be used, and 

 the butter should not have been melted. 



Annatto and other Colouring Matters. If the colouring 

 matter of a butter can be extracted with alcohol, foreign 

 colours are present, as the natural colouring matter is not 

 soluble in alcohol. Annatto may be detected by extraction 

 with methyl alcohol and carbon disulphide. The latter 

 dissolves the fat and sinks, the alcohol dissolves the colour 

 and floats. Separate alcohol and evaporate : yellow stain, 

 which turns blue-green on adding a drop of strong sulphuric. 

 Turmeric, saffron, saffronette, marigold, and the azo dyes 

 are also used. 



Butter v. Margarine. 



i. Digest fat of sample with alcoholic solution NaOH, 

 when butter gives pleasant odour of butyric ether or 

 pineapples, and pure margarine gives a tallow smell. 



2. Burn a small piece of sample on platinum foil and 

 extinguish flame : butter, rather pleasant smell ; 

 margarine, tallow smell. 



3. Melting-point of fat. Take a platinum loopful, dip 

 in water alongside thermometer, and heat until fat just 

 translucent : butter fat, 30 to.35 C. ; margarine fat, rarely 

 above 28 C ; coco-nut oil, 20-26 C. 



4. Valenta test. 



* CHEESE. 



Cheese is made from milk by the action of rennet, and 

 consists of coagulated casein with varying proportions of 

 water, fat, and salts. It may be made from whole milk 

 (Cheddar, Cheshire, Gloucester, and some American 

 cheeses), from skimmed milk (Dutch, Parmesan, Suffolk, 

 and Somerset cheeses), from whole milk and cream (Stilton). 

 Parmesan is made from goat's milk (partly skimmed) ; 

 Roquefort from ewe's milk (partly skimmed) ; and Gorgon- 

 zola by adding in the process of manufacture, powdered bread 

 crusts on which moulds have been allowed to grow. Cream 

 cheese consists of the fresh curd which has been moderately 

 pressed, and is eaten before being allowed to ripen. 

 " Ripening " of cheese is supposed to be a decomposition 

 whereby the casein undergoes a fatty change with the 



