Skin and Seed Tannin Extraction during Red Wine Fermentations.
To manage tannins in red wine fermentations optimally, winemakers would like to know
the following: 1) when tannins are extracted during alcoholic fermentation, 2) from
which part of the grape (seed or skin) the tannins are derived, and 3) from where in the
tank the extraction occurs (i.e.: does seed tannin extraction at the bottom of the fermenter
contribute significantly to the tannins in red wine?).
The purpose of this investigation is to better understand the tannin extraction process
from grapes into must/wine during maceration. This year, experiments were conducted
on cultivar Pinot noir in commercial-scale open-top fermenters and with cap management
by punchdown. Wine samples were taken daily during the alcoholic fermentation until
dry, and at 3 different depths in the tank: bottom, middle and top (in the cap). For each
sample, the amount of total tannins and the proportion of skin and seed tannins were
determined. At the peak of alcoholic fermentation a large amount of skin tannin was
released from the cap, with an increasing amount of seed tannin extracted with time. At
the end of fermentation, ~50%of the tannin was seed-derived. Samples collected from
the bottom of the tank indicated little seed tannin extraction, suggesting that seed tannin
is extracted from the cap.
In parallel, fruit harvested in the same block was managed by pumpover instead of
punchdown. Based upon this experiment, the rate of seed tannin extraction exceeded skin
tannin extraction when the cap was managed by punchdown. This study also investigated
seed and skin tannin extraction as a function of plant vigor. The results indicate that skin
tannin changes in wine a far greater than those derived from the seed.