The Formation of Acetoin and Diacetyl during Fermentation, and the levels found in Wines

Abstract

Acetylmethylcarbinol (acetoin) formed during yeast fermentations of sugar reaches a maximum of about 25 to 100 ppm about midway through fermentation, and then largely disappears, presumably by reduction to 2,3-butanediol. The peak of acetoin content coincided with the maximum level of acetaldehyde formation, which follows a similar pattern of rise and decline. The acetoin content of sweet (dessert) wines produced by the addition of wine spirits to half fermentation was much higher (50 to 200 ppm) than corresponding dry wines produced by complete fermentation (about 5 to 20 ppm). Significantly higher levels of acetoin (up to 350 ppm) were found in sherry samples produced by the submerged flor yeast fermentation than in those of comparable baked-type sherry. However, diacetyl was not higher (less than 1 ppm) as a result of the oxidative conditions of the submerged flor process. The creatine-αnaphthol colorimetric method was used for acetoin for measurement, but it gave erroneously high values for diacetyl in the presence of acetoin, so diacetyl was determined by a colorimetric nickel dimethylglyoxime method. The possible significance of acetoinic compounds in wines is discussed.