FRUITS AND THEIR COMPOSITION. 309 



Tables V. and VI. represent the proportion in which the solu- 

 ble constituents of the fruits are found in the juice or must ob- 

 tained from them ; in the practical execution of the fabrication of 

 fruit wines we will have occasion to refer to these tables. 



For the preparation of wine only the soluble substances, which 

 pass into the must and from which the wine is formed, are chiefly 

 of interest, and it will be necessary to consider them somewhat 

 more closely. 



Grape-sugar or glucose. This sugar is widely diffused through- 

 out the vegetable kingdom, occurring in most kinds of sweet fruits, 

 in honey, etc. Artificially it can be readily obtained by heating a 

 solution of cane sugar with a dilute acid ; it is also formed by 

 dissolving cane sugar in wine. On a large scale it is prepared 

 by boiling starch with very dilute sulphuric acid for several 

 hours, neutralizing the liquid with chalk and evaporating the 

 solution. 



Grape-sugar is much less sweet than cane-sugar ; in alcohol of 

 90 per Tr. it is sparingly soluble ; in hot water it dissolves in 

 every proportion; of cold water it requires, however, about 1J 

 parts for solution. It crystallizes from an aqueous solution with 

 one molecule of water in cauliflower-like masses and from hot 

 alcohol in warty, anhydrous needles. A solution of crystallized 

 grape-sugar turns the plane of polarization to the right, but one 

 of anhydrous grape-sugar to the left. 



Acids. The acid reaction of fruit juices is partly due to 

 malic acid and partly to citric acid, and also, as in the case of 

 grapes, to tartaric acid. As a rule all these acids are present ; in 

 currants citric acid predominates; in apples, etc., malic acid. 



The presence of potassium in grape-must gives rise to the for- 

 mation of potassium bitartrate or crude tartar. Tartar requires 

 for its solution 240 parts of cold water; in alcoholic fluids it is less 

 soluble, and hence it is found as a crystalline deposit in wine 

 casks. Fruit-musts contain no tartaric acid, and, consequently, 

 the wines prepared from them cannot deposit tartar. The salts 

 formed by malic and citric acids with potassium being readily 

 soluble and even deliquescent form no deposit in the wine. 



Albuminous substances. By this general term are designated 

 several nitrogenous vegetable substances which have the same 



