v DECOMPOSITION PRODUCTS 233 



The bisulphite solution is added to the fuschiri solution, and 

 an hour later, when the decolorisation is almost complete, the 

 hydrochloric acid is added. The test is carried out by shaking 

 2 c c. of the distillate from the butter with 1 c.c. of the reagent 

 and then allowing the mixture to stand. In the presence of 

 aldehyde, a violet colour, which gradually deepens, soon becomes 

 apparent. 



III. DECOMPOSITION PRODUCTS OF CHEESE. 



Introductory. 



The decomposition of cheese, which is known as " ripening," 

 is a process which can be modified artificially in certain direc- 

 tions, and is more or less thorough according to the kind of 

 cheese which is being made. The main features of the 

 chemical changes involved in ripening have already been 

 sketched in the introduction to the chapter on the analysis of 

 cheese (p. 182). 1 



1 Determination of the Degree of Acidity. 



In this determination the cheese itself must be titrated, and 

 not an aqueous extract of it, for the acids arising from the 

 fermentation of the milk sugar are mainly in combination with 

 the lime of the phosphate and the paracasein. 2 



Ten g. of cheese are well ground in a mortar with water at 

 40-45 C. The emulsion is diluted to 100 c.c. and titrated 

 with JV/4 alkali, phenolphthalein being used as indicator. The 

 number of cubic centimetres of N/4< alkali is multiplied by 10, 

 and gives the degree of acidity of the cheese. This deter- 

 mination is analogous to the one for the degree of acidity of 

 milk. 



2 Volatile Fatty Acids. 



The volatile fatty acids in cheese are determined in the same 

 way as those of milk (p. 219). One hundred g. of an average 



1 A detailed description of the bacteriological processes which goon in milk 

 and dairy products will be found in the author's Bakterioloyie dea Meirerei- 

 wesens, published by M. Heinsius Nachfolger, Leipsic. 



2 Orla Jensen, " Ueber die im p]nunentaler Kiise stattfindende Milch- 

 sauregarung, Landwirt. Jahrbuch der Schweiz, 1906. 



