VINOUS FERMENTATION. 



105 



volatile liquids are formed by a mutual in- 

 terchange of the elements of gluten and 

 sugar, in consequence, therefore, of a true 

 process of putrefaction, still it is certain, that 

 other causes exercise an influence upon their 

 production and peculiarities. 



The substances in wine to which its taste 

 and smell are owing, are generated during 

 the fermentation of the juice of such grapes 

 as contain a certain quantity of tartaric acid ; 

 they are not found in wines which are free 

 from all acid, or which contain a different 

 organic acid, such as acetic acid. 



The wines of warm climates possess no 

 odour ; wines grown in France have it in a 

 marked degree, but in the wines from the 

 Rhine the perfume is most intense. The 

 kinds of grapes on the Rhine, which ripen 

 very late, and scarcely ever completely, such 

 as the Riessling and Orleans, have the 

 strongest perfume or bouquet, and contain, 

 proportionally, a larger quantity of tartaric 

 acid. The earlier grapes, such as the Rw- 

 lander, and others, contain a large propor- 

 tion of alcohol, and are similar to Spanish 

 wines in their flavour, but they possess no 

 bouquet. 



The grapes grown at the Cape, from 

 Riesslings transplanted from the Rhine, 

 produce an excellent wine, which does not, 

 however, possess the aroma which distin- 

 guishes Rhenish wine. 



It is evident from these facts, that the acid 

 of wines, and their characteristic perfumes, 

 have some connexion, for they are always 

 iound together; and it can scarcely be 

 doubted that the presence of the former 

 exercises a certain influence on the forma- 

 tion of the latter. This influence is very 

 plainly observed in the fermentation of li- 

 quids, which are quite free from tartaric 

 acid, and particularly of those which are 

 nearly neutral or alkaline, such as the mash* 

 of potatoes or corn. 



The brandy obtained from corn and pota- 

 toes contains an ethereal oil of a similar com- 

 position in both, to which these liquors owe 

 their peculiar smell. This oil is generated 

 during the fermentation of the mash ; it exists 

 ready formed in the fermented liquids, and 

 distils over with alcohol, when a gentle heat 

 is applied. 



It is observed that a greater quantity of 

 alcohol is obtained when the mash is made 

 quite neutral by means of ashes or carbonate 

 of lime, but that the proportion of oil in the 

 brandy is also increased. 



Now it is known that brandy made from 

 potato starch, which has been converted 

 into sugar by dilute sulphuric acid, is com- 

 pletely free ' from the potato oil, so that 

 this substance must be generated in con- 

 sequence of a change suffered by the cel- 

 lular tissue of the potatoes during their 

 fermentation. 



* Mash is the mixture of malt, potatoes, and 

 water, in the mash tun, a large vessel in which it 

 te infused. 



14 



Experience has shown that the simulta- 

 neous fermentation or putrefaction of the 

 cellular tissue, by which this oil is generated, 

 may be completely prevented in the fabrica- 

 tion of brandy from corn.* 



The same malt, which in the preparation 

 of brandy yields a fluid containing the oil of 

 which we are speaking, affords in the for 

 mation of beer a spirituous liquor, in which 

 no trace of that oil can be detected. The 

 principal difference in the preparation of the 

 two liquids is, that in the fermentation of 

 wort, an aromatic substance (hops) is added, 

 and it is certain that its presence modifies 

 the transformations which take place. Now 

 it is known that the volatile oil of mustard, 

 and the empyreumatic oils, arrest completely 

 the action of yeast ; and although the oil of 

 hops does not possess this property, still it 

 diminishes, in a great degree, the influence 

 of decomposing azotised bodies upon the 

 conversion of alcohol into acetic acid. There 

 is, therefore, reason to believe that some 

 aromatic substances, when added to ferment- 

 ing mixtures, are capable of producing very 

 various modifications in the nature of the 

 producls generated. 



Whatever opinion, however, may be held 

 regarding the origin of the volatile odorife- 

 rous substances obtained in the fermentation 

 of wine, it is quite certain that the charac- 

 teristic smell of wine is owing to an ether 

 of an organic acid, resembling one of the 

 fatty acids (oenanthic ether.) 



It is only in liquids which contain other 

 very soluble acids, that the fatty acids and 

 cenanthic acids are capable of entering into 

 combination with the ether of alcohol, and 

 of thus producing compounds of a peculiar 

 smell. This ether is found ..in all wines 

 which contain free acid, and is absent from 

 those in which no acids are present. This 

 acid, therefore, is the means by which the 

 smell is produced; since without its presence 

 cenanthic ether could not be formed. 



The greatest part of the oil of brandy 

 made from corn consists of a fatty acid not 

 converted into ether; it dissolves oxide of 

 copper and metallic oxides in general, and 

 combines with the alkalies. 



The principal constituent of this oil is an 

 acid identical in composition with cenanthic 

 acid, but different in properties. (Mulder.) 

 It is formed in fermenting liquids, which, if 

 they be acid, contain only acetic acid, a body 

 which has no influence in causing other 

 acids to form ethers. 



The oil of brandy made from potatoes is 

 the hydrate of an organic base analogous to 

 ether, and capable, therefore, of entering into 

 combination with acids. It is formed in 

 considerable quantity in fermenting liquids 

 which are slightly alkaline; under circum- 



* In the manufactory of M. Dubrunfaut, so con- 

 siderable a quantity of this oil is obtained under 

 certain circumstances from brandy made from 

 potatoes, that it might be employed for the pur 

 pose of illuminating his whole manufactory. 



