Abstract
This review intends to rationalize the knowledge related to the aroma of grapes and to the aroma of wine with specific origin in molecules formed in grapes. The actual flavor of grapes is formed by the few free aroma molecules already found in the pulp and in the skin, plus by those aroma molecules quickly formed by enzymatic/catalytic reactions. The review covers key aroma components of aromatic grapes, raisins and raisinized grapes, and the aroma components responsible from green and vegetal notes. This knowledge is used to explain the flavor properties of neutral grapes. The aroma potential of grape is the consequence of five different systems/pools of specific aroma precursors that during fermentation and/or aging, release wine varietal aroma. In total, 27 relevant wine aroma compounds can be considered that proceed from grape specific precursors. Some of them are immediately formed during fermentation, while some others require long aging time to accumulate. Precursors are glycosides, glutathionyl and cysteinyl conjugates, and other non-volatile molecules.
Highlights
Winemaking grapes are quite unique fruits because they are grown not to be immediately consumed, but to make wine with them. From this point of view, the study of grape aroma cannot be limited to the pool of molecules directly responsible for the odors and flavors of grape and grape juice but has to include those other chemical structures that, more or less directly, are specific precursors of relevant wine aroma molecules
The first one addresses the aroma molecules of those types of grapes showing at 5-times wine concentration and in the absence of wine volatiles, which may call into question the sensory relevance of the aroma volatiles released from those glycosides in the mouth [20]
The first type of molecules includes a series of polyols discovered more than 30 years ago which by chemical rearrangements induced by the acid hydrolysis at wine pH produce different aroma active terpenols [2]
Summary
Winemaking grapes are quite unique fruits because they are grown not to be immediately consumed, but to make wine with them From this point of view, the study of grape aroma cannot be limited to the pool of molecules directly responsible for the odors and flavors of grape and grape juice but has to include those other chemical structures that, more or less directly, are specific precursors of relevant wine aroma molecules. 1. Scheme showing main systems/pools in grape of specific precursors of aroma molecules andand their involvement in the development of wine varietal aroma andand flavor. For neutral varieties things are slightly more complicated, since the precursors of some relevant aroma molecules, such as norisoprenoids, require acid catalysis to undergo the chemical rearrangement processes through which the odorant is formed This implies that labile aroma molecules, such as linalool and geraniol, will be degraded [9]. Potential grape aroma refers to the different grape molecules and grape chemical systems that are specific precursors of relevant wine odorants
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