FUSEL OIL, a term applied to a mixture of volatile oily liquids of characteristic odour and taste which arises during the fermentation of potatoes, beetroots, grain, and the "mare" of grapes. The amount produced is comparatively small, the pro portion being largest in the case of potatoes. When such fet mented liquors are submitted to distillation the various alcohols present become partially separated, owing to their varying vola tilities. Ethyl alcohol (wine spirit) distils over first and the fusel oil containing several other alcohols is then collected in the distillate obtained at temperatures ranging from 1 o 5 ° to 137° C. Fusel oil consists mainly of two higher alcohols (q.v.) distilling between 128° and 132° C; one of these is inactive isoamyl alcohol or isobutylcarbinol, and the other is active amyl alcohol or secondary butylcarbinol, the latter is laevo-rotatory, i.e., rotates the plane of polarized light to the left, and the former is optically inactive. These oily alcohols are partially miscible with water, dissolving in about 40 parts at 14° C. A more volatile constituent of fusel oil, isobutyl alcohol, is found in the distil lates boiling between 1o5° and 520° C; it dissolves in in parts of water at 15° C. In small doses fusel oil causes thirst and headache; in larger doses it is a convulsive poison.
The amyl alcohols present in fusel oil are largely used in the manufacture of amyl acetate, a fragrant liquid used in flavouring essences (pear oil, etc.), in confectionery and as a solvent in making varnishes, lacquers and artificial leathers having a nitro cellulose composition. Fusel oil is used as a solvent for alkaloids and fats; it is employed in the flotation process for separating sulphide ores and is the starting material in a process for syn thetic rubber.
See the article "Fusel Oil" in Thorpe's Dictionary of Applied Chem istry, vol. iii. (1922). (G. T. M.)