The flavor of alcoholic beverages is produced by a very large number of compounds (50). Among these, acetoin is important because of its involvement in the bouquet of wine, and it is the key compound in the biosynthesis of 2,3-butanediol and diacetyl. These two compounds are closely related to acetoin, representing three levels of oxidation in one four-carbon skeleton (8). Their contribution to the aroma and flavor of wine is not easily assessed. Neither 2,3-butanediol nor acetoin is strongly odorous; in fact, their threshold values in wine are very high, both being about 150 mg/liter (19, 72); however, diacetyl, which creates an off flavor in alcoholic beverages, has a characteristic odor and is detectable in wine at very low levels (threshold value, 8 mg/liter) (19). In this picture, the flavor significance of acetoin is more likely to be attributable to its potential aroma than to the odor itself.