Malic Acid as a Potential Marker for the Aroma Compounds of "Amarone Wine" Grape Varieties in Withering

Amarone is a wine produced from withered grapes of Corvina, Corvinone, and Rondinella varieties. The berries’ water loss in the withering process, combined with berry senescence, results in significant metabolic changes. Here, we report on changes in malic acid, total polyphenols, and aroma compounds of three single Amarone varieties during withering. Grape bunches of the three varieties were withered in a commercial facility, and weight loss (WL) was measured to determine the time of sampling of grapes for analyses (10, 20, 30, and 50% WL). Rondinella grapes lost weight faster than did Corvina and Corvinone grapes. Malic acid decreased rapidly in all varieties, but in Rondinella grapes with 20% WL, malic acid subsequently increased. Total polyphenols rose slightly in grapes with 20% WL, and their content then increased more than could be attributed to concentration effects. At harvest, the aroma compounds that were initially present at high concentrations and decreased during withering were 6-methoxy-3-methylbenzofuran; 4-vinylguaiacol; 3,4,5-trimethoxybenzyl alcohol; vomifoliol; and coumaran, which were detected in all varieties, reaching the highest concentrations in Corvinone. During withering, most of these markers showed a peak at 10% or 20% WL in Rondinella grapes, whereas in Corvinone, they peaked at 20% WL as in Corvina grapes, which also exhibited a concentration peak of some compounds at 30% WL. We conclude that not all grape varieties behave in the same way in withering; therefore, it is necessary that winemakers know the weight loss (and the time) at which the best aromatic expression is reached to determine the optimal processing stage of a variety. By matching malic acid trends with those of aroma compounds, we propose that malic acid could be a useful tool for monitoring the changes in aroma compounds during grape withering.