2o6 CHEESE 



cially, in order that it may be put on the market with the same 

 colour all the year round, and the artificial colouring matter used 

 for this purpose is most usually annatto, a natural yellow substance 

 obtained from the fruit-capsules of Bixa orellana. The dye is 

 dissolved in olive or other oil, and the solution added in small 

 amount to the cream before churning. Other natural colouring 

 matters are sometimes employed and may be regarded as innocuous ; 

 the use of aniline dyes is, however, to be deprecated, while lead 

 chromate, which has been used, is distinctly poisonous. 



196. Detection of Artificial Colouring Matter, 



Annatto. — About 5 grams of butter are dissolved in 

 50 c.c. ether, and about 10 c.c. of dilute caustic soda 

 added. The mixture is thoroughly shaken, allowed to 

 stand for a short time, and the brown alkaline liquid 

 containing the colouring matter dissolved in it is 

 separated off and evaporated to dryness. One drop of 

 strong sulphuric acid is then added, and the production 

 of a blue colour changing to green shows the presence 

 of annatto. 



Yellow Aniline Dyes. — A few grams of butter are 

 melted and shaken up with an equal volume of strong 

 HCl. The acid will be coloured red in the presence of 

 most aniline dyes. 



CHAPTER XXI 

 Cheese 



The casein in milk appears to exist in a state of colloidal 

 suspension, and is loosely combined with the calcium salts also 

 present. These calcium compounds undergo a change under the 

 action either of rennet or acids, whereby there is precipitated an 

 insoluble curdy substance, the nature of which varies in the two 

 cases. 



In the case of the precipitation by acids, the latter form soluble 



