Red wines develop through oxidation and other aging mechanisms. Limited oxidative changes, such as color stabilization and “softening” of tannins, are desirable and contribute to wine quality and complexity. Investigations into the effects of microoxygenation on wine composition have revealed continuous oxygen consumption, yet no specific substances have proved to be useful markers for monitoring wine development. Even acetaldehyde, perhaps the major product of wine oxidation, does not appear to accumulate in microoxygenated wines. Its presence is transient because it rapidly undergoes reaction with various wine components. We believe these reactions lead to sinks into which acetaldehyde flows, some of which are hidden from common analytical methods. To overcome these shortcomings, we investigated the fate of acetaldehyde with Nuclear Magnetic Resonance Spectroscopy (NMR), a direct method that does not alter the sample prior to analysis and detects any substance in equal measure. Thus, it is an integral instrument to detect any form or product of acetaldehyde. One- and two-dimensional NMR was applied to analyze relevant acetaldehyde reactions with known nucleophiles (sulfites, thiols, alcohols, and flavonoids) in model wine solutions to establish basic properties of each reaction. In addition, free acetaldehyde and some of its derivatives were measured in microoxygenated wines to make sense of the inexplicable results obtained through routine analysis methods (Aeration-oxidation, HPLC-MS). Consequently, NMR measurements have begun to reveal the fate of acetaldehyde in wine: the outcome of oxidation. With this information, we hope to provide a means to predict the distribution of acetaldehyde created by oxidation into its various forms, based on a wine’s composition. Given a more accurate picture of the anticipated content and the various forms of acetaldehyde, we can begin to make more predictive decisions on oxygen treatments.

Funding Support: American Viticulture Foundation and UC Davis Viticulture Department Scholarships