An odorless flavor precursor fraction extracted from different nonfloral grape varietals has been added to a grape must and has been fermented by three different yeast strains. The wines obtained were analyzed by sensory descriptive analysis and by gas chromatography mass spectrometry to determine more than 90 aroma chemicals. The addition of the precursor fraction brought about a significant increase of the wine floral notes, irrespective of the yeast used. The levels of 51 wine aroma chemicals were found to depend on the precursor fraction addition and, in most cases, also on the yeast strain. Only beta-damascenone, beta-ionone, and vinylphenols were produced at concentrations well above threshold. However, the concerted addition of groups of compounds has shown that lactones, cinnamates, vanillins, and terpenes are together active contributors to the floral note. Different observations suggest that the formation of varietal aroma is an integral part of yeast metabolism and not a simple hydrolytical process.

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Precursor extracts obtained from different grape varieties were submitted to harsh acid hydrolysis (pH 2.5, 100 degrees C, 1 h) and enzymatic hydrolysis (AR2000, pH 5, 40 degrees C, 16 h) and were also added to a synthetic must (200 g L(-1) glucose), which was fermented (yeast strain Stellevin NT 116), to compare the "natural hydrolysis" carried by yeast with alternative "fast" hydrolytic strategies. In all cases, released volatile compounds were extracted by SPE and determined by GC-MS. Leaving aside Muscat, differences between varieties were not relevant, although Grenache and Chardonnay presented some key peculiarities. In general, alcoholic fermentation showed the lowest potential to release volatile compounds from aromatic precursors, whereas enzymatic hydrolysis was the most efficient but also the most different. Practically, this implies that the predictive ability of this hydrolytic strategy is rather poor. In contrast, harsh acid hydrolysis can be considered to much more adequately measure the aroma potential of grapes for winemaking, which suggests that transformations taking place during fermentation include relevant chemical rearrangements in acid media that are better predicted by acid hydrolysis.

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