Influence of Grape and Wine Production Practices on Tannin Extractability and Activity

The primary objective of this proposal has been to develop an analytical method that predicts tannin interaction with salivary protein. This method is unique in that it moves away from tannin concentration as a predictor of astringency so that the impact of tannin structure variation (e.g.: color incorporation, oxidation of tannin structure) on interaction, can be measured. This analytical approach follows previous work which found that tannin structure variation related to grape maturity and wine age, could be related to thermodynamics of interaction.

Coupled to the development of an analytical method, this project also focused on the development of a rapid reproducible method for preparing extracts from grape berries. This method deviates from many extraction methods developed to date in that it does not rely on the addition of solvents to mimic a wine-like system. Instead, this extraction method imposes a mechanical stress on berries for a short period of time (5 min), thereby testing the robustness of plant cells and hypothesized durability of diffusional barriers. The two methods above are expected to provide new and novel information on tannin development, from grapes to wine. The objectives of this proposal are consistent with the highest priority research objective as outlined by the American Vineyard Foundation. The results to date have been very positive.

First, a new analytical method has been developed and is now being applied to grape extracts and wines. The analytical method has the ability to measure tannin interaction variation that would be consistent with “softening” and therefore has significant potential in managing grape and wine production operations. Importantly, the analytical method is able to measure the impact of tannin modification on the “stickiness” of tannins. With regard to the new extraction method, the results have also been successful in that extracts prepared from the developed extraction procedure have been associated with predicted differences based upon growing region and historical block differences in tannin quality.

The results from the first two years have led to the development of analytical methods for tannin assessment in grapes and wine. In year three of this project, research efforts are being directed to the development a more complete understanding of the utility of these new methods.