Higher alcohols, diacetyl, acetoin and 2,3-butanediol biosynthesis in grapes undergoing carbonic maceration

Two grape varieties, Baco Noir and Gamay, were subjected to carbonic maceration (CM) conditions for 3, 6, 9, 12 and 15 days and the levels of higher alcohols, diacetyl, acetoin and 2,3-butanediol were determined. Diacetyl was not present in any of the CM juices. Acetoin and 2,3-butanediol were produced in the grapes and their amounts increased as the time of CM increased. On the 15th day of CM, acetoin was 12.6 ± 0.9 mg/l in Baco Noir juice and 3.2 ± 0.1 mg/l in Gamay juice, and 2,3-butanediol was 68.2 ±  3.9 mg/l in Baco Noir juice and 19.9 ± 1.2 mg/l in Gamay juice. 1-propanol, 2-methyl-1-propanol, 3-methyl-1-butanol, 2-methyl-1-butanol appeared in trace amounts (the highest among them was 3.3 ± 0.0 mg/l) in the CM Baco Noir juices and were not detected in the CM Gamay juices. Based on these results, the sensory contribution of higher alcohols from grape CM would be inconsequential when compared to that from yeast metabolism.