VOLATILE ACIDS AND ALDEHYDES. 499 



of BUCHNER and MEISESIIEIMEII (IV.) having proved this acid to be 

 a normal by-product of that phenomenon. It is true that the 

 amount so produced is small, though, according to THYLMANN and 

 HILGER (I.), it is greater when the solution contains a higher 

 proportion (30-40 per cent.) of sugar. When it is formed to any 

 extent otherwise, its production should perhaps be attributed to 

 the oxidation of the alcohol, probably with the assistance of 

 bacteria. Acetic acid, though only in small quantities, is also 

 found in fusel oils. 



The third member of the fatty-acid series is propionic acid, 

 which was found by WINKLER (II.) and BECHAMP (XIV.) in 

 diseased wines. According to ORDONNEAU (I.), it is also occasionally 

 present, as an ester, in cognac. STRECKER (I.) and KRAMER (1.) 

 attribute its origin to lactic acid, in the case of certain fermenta- 

 tions a point worthy of note, seeing that this acid is a normal 

 by-product of alcoholic fermentation. 



Butyric acid, which is readily produced by certain bacteria, 

 was detected either in the free state, or more frequently 

 combined as an ester in cognac by DUCLAUX (XXVIII.) and 

 ORDONNEAU (I.), and in potato fusel oil and cherry brandy by K. 

 WINDISCH (III. and IV.). 



Valeric acid was found by KRUIS and RAYMAN (II.) in a 

 sterilised wort that had been kept for several years. They 

 ascribed its origin as well as that of the other higher fatty acids 

 still to be mentioned to the decomposition of complex nitrogenous 

 foodstuffs, e.g., protein. DUCLAUX (XXVIII.) has also found it 

 occasionally in diseased wines. 



Among the higher fatty acids, caproic acid, caprylic acid, 

 pelargonic acid and capric acid occur, in combination with alcohols 

 as esters, in the fusel oils (see next paragraph) and in cognac, 

 whilst oenanthylic acid appears only in wine, or cognac. On this 

 point see PELOUZE and LIEBIG (I.), DELFFS (I.), FEHLING (I.), 

 A. FISCHER (I.), GRIMM (I.), DUCLAUX (XXVIII.), OBDONNEAU 

 (I.), K. WINDISCH (III. and IV.), KRUIS and RAYMAN (II.), and 



SCHUPPHAUS (I.). 



Taking the total fatty acids as representing 100, WINDISCH (III.) 

 gives the proportions of the individual fatty acids in the esters as 

 follow: in potato fusel oil 3.5 of acetic acid, 0.5 of butyric acid, 14 

 of caproic acid, 34 of caprylic acid, 1 2 of pelargonic acid, and 36 of 

 capric acid ; in corn fusel oil, acetic acid 2.7, butyric acid 0.4, 

 caproic acid 13.2, caprylic acid 26.7, pelargonic acid 1 2.9, and capric 

 acid 44.1. HILGER (I.) also found stearic acid, palmitic acid and 

 lauric acid in a sample of corn spirit. These acids originate un- 

 doubtedly from decomposed fat ; and it is highly probable that 

 the other higher fatty acids, from butyric acid to capric acid, are 

 produced from the fat (see p. 494, vol. ii.) contained in the mash 

 and in the yeast cells, as the result of decomposition by yeast 

 lipase; compare BAU (XXII.). . 



