BEER FLAVOUR. IV. FACTORS AFFECTING THE PRODUCTION OF FUSEL OIL

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Abstract
Production of fusel oil during fermentation is greatly influenced by (i) yeast strain, (ii) temperature, (iii) composition of wort and (iv) method of fermentation. At 77° F., top yeasts differ in the amount of fusel oil they produce, but all form more than do bottom yeasts. At 50° F., however, both top and bottom yeasts yield about the same amount, production by the bottom yeasts not changing greatly with the decrease in temperature. The fusel oil is produced throughout primary and secondary fermentations, but little is produced when yeast autolyses in the beer. The fusel oil content of beer produced under conventional conditions is somewhat lower than in beer made in stirred batch and accumulating batch fermentations; under conditions of continuous fermentation the amounts formed are slightly greater than those in conventional beers. Additions of leucine to wort increase the level of fusel oil in the final beer, but increases in the proportion of sugar depress the amount of fusel oil. This supports the view that the bulk of beer fusel oils are produced from amino acids via the Ehrlich pathway; nevertheless, a low level of fusel oil is still produced in a defined synthetic medium containing no amino acids and more is produced under anaerobic than under aerobic conditions.