β -Phenethanol and n-hexanol in wines: Influence of yeast starin, grape variety and other factors; and taste thresholds

Abstract

β-Phenethanol and n-hexanol were measured by gas chromatography in a wide range of commercial and experimental wines. Commercial wines ranged from 5 to 74 ppm β-phenethanol and 1.3 to 12 ppm n-hexanol. Dry red wines and fino sherries were high in p'-phenethanol, and ports, muscats (both sweet dessert wines) and dry red wines were high in n-hexanol. The strain of yeast strongly influenced formation of β-phenethanol. Mean yields by eight yeasts (Saccharomyces) during fermentation of grape juices from three varieties of Vitis vinifera under comparable conditions ranged from 5.6 to 20 ppm. The strain of yeast had little effect on amounts of n-hexanol in the wines. Varieties of V. vinifera differed in amounts of β-phenethanol and n-hexanol formed in the wines made therefrom, irrespective of the yeast strain used. Wines made from Shiraz (Syrah) grapes were characterised by high levels of fi-phenethanol in comparison with white grape varieties examined. The year of vintage influenced amounts of β-phenethanol in wines, and the soil type and viticultural area also effected the amounts of both β-phenethanol and n-hexanol formed. More β-phenethanol was formed by fermentation at 15° C and 25° C than at 35° C, and more was formed at pH 3.5 and 4.0 than at pH 3.0. n-Hexanol content was not influenced significantly by either temperature of fermentation or pH of the must. Addition of β-phenylalanine to the must resulted in formation of more β-phenethanol by fermentation, and the mechanism of formation of both β-phenethanol and n-hexanol is discussed . Taste thresholds were measured as minimum detectable differences in a Riesling dry white wine. Values for different tasters ranged from 30 to > 200 ppm for β-phenethanol (10 tasters) and 4 to > 30 ppm for n-hexanol (9 tasters). Added β-phenethanol, but not n-hexanol, was considered to improve the quality of the wine.