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Proanthocyanidins are a grape-derived phenolic class of compound that provide wine with bitterness and astringency. Because of this, proanthocyanidins are considered to be essential components of wine quality. Proanthocyanidins are localized in the seed, skin and stem tissue of the grape berry and the composition of proanthocyanidins will vary depending on the tissue of origin.
Empirical evidence suggests that proanthocyanidins that are seed-derived impart harsh and aggressive tannins to red wine, and minimizing the crushing of fruit prior to fermentation and maceration will minimize the extraction of seed material. There are however, few studies that provide conclusive evidence of this.
In the present study micro-fermentations (4 kg fruit) were conducted on Vitis Vinifera L. cv. Merlot berries that were crushed to varying degrees. Five treatments were established varying from 0-100% crushed berries. Samples were collected throughout fermentation and of the free run and press wine at the time of pressing..Grape and wine extracts were subjected to phloroglucinolysis to determine the amount and proportional extraction of seed and skin proanthocyanidins.
Overall total proanthocyanidin extraction followed an exponential model, consistent with previous studies. Regardless of the treatment, and increase in total proanthocyanidin extraction was observed during fermentation. Moreover, it was observed that crushing increased the rate at which proanthocyanidins were extracted. Contrary to conventional wisdom, the highest skin concentration or percent composition was not obtained in the treatments that had fewer crushed berries. For all treatments, skin proanthocyanidin extraction reached a maximum prior to pressing while seed proanthocyanidins increased throughout maceration. The highest skin proportion was reached by the treatment with 75% crushed berries at day 10, little past half of the fermentation time. |
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