Fining with purified grape pomace. Effect of dose, contact time and varietal origin on the final wine phenolic composition

Fining, which involves the addition of adsorptive material in order to reduce or eliminate certain unwanted components, is a common winemaking practice. Fining agents affect the wine phenolic compounds, some of which may be reduced. When this reduction is experimented by the tannins, a positive effect may result by decreasing astringency in the wine, although a decrease in the wine color may also take place when the anthocyanins are involved, affecting its quality. Recently, grape cell wall material has been tested as a potential fining agent in wines, since it shows a high affinity for tannins so that its use could reduce wine astringency. In this work, the use of purified grape pomace as fining agent is proposed and the effect of different doses and contact times on wine chromatic characteristics was investigated as well as how differences in the composition of the purified pomace could alter the phenolic composition of a red wine. The results showed that a Monastrell purified grape pomace dose of 6 mg/ml and a contact time of 5 days could be suitable for decreasing the wine tannin content without producing great changes in the wine chromatic characteristics. When comparing the effect of purified pomaces from four grape varieties, some differences in their capacity to interact with the wine tannins and anthocyanins were found, however, the results confirm that the purified grape pomace, a byproduct of the enology industry could be a new interesting fining material.