Accounting for the partitioning of extractable and bound tannin fractions during commercial pinot noir fermentations

Tannins, or proanthocyanidins, are key components of wine known for their influence on astringency, ageability and color stability over time. Understanding the extraction of tannin from grapes into wine is an important factor in forecasting viticultural decisions and winemaking adjustments during harvest and fermentation. In previous work it was noted that not all tannin found in the fruit can be accounted for in the finished wine. In addition, it is not possible to predict what amount of the tannin found in fruit will end up in wine on a consistent basis.;Five commercial Pinot noir lots ranging in fruit harvest weights of 517 to 1,098 kilograms were sampled in order to account for the total tannin present throughout processing, from grape to wine. Samples were taken as fruit, at pressing after primary fermentation, and after secondary fermentation as wine. Skins, seeds and mesocarp (the fleshy berry pulp) from the fruit, along with the pomace, lees and seeds taken from the tanks were all ground separately in liquid nitrogen, and extracted with 70% acetone for phenolic analysis by use of the Adams-Harbertson Tannin Assay. The cell wall materials from these components were used, after acetone extraction, for the measurement of the cell wall binding potential, as well as the measurement of the "bound" tannins present by use of a common acid-butanol method for the analysis of proanthocyanidins. The extractable tannin measurements of the post-fermentation components were able to account for only 40% to 63% of the tannin initially present in the corresponding fruit. Further measurements of "bound" tannins indicate that the inclusion of this portion while accounting for tannin was able to largely explain the whereabouts of the missing tannin, with a recovery range of 70% to 108% of the total tannin in the fruit. The variable tannin accounting can be mostly explained by a margin of error and the inclusion of a whole cluster fermentation lot, which may have skewed "bound" tannin values for that lot. Although there is still room for refinement to the accounting of tannin by this method, those lots that are still missing tannin after the inclusion of the "bound" tannin are much closer to the original fruit tannin concentrations than they were without this consideration.