Grape seed powder as an alternative to bentonite for wine fining

PR proteins can cause haze in wines, and the risk is to keep the wine unsold. Generally, in winemaking bentonite solves this problem by removing proteins, but it is not a renewable resource, has poor settling, which means difficulty in filtering after use and a considerable loss of wine, it is not a specific adsorbent and may reduce aromas and flavor compounds. This work studied the use of grape seeds powder (GSP) to remove haze-forming proteins from wine and grape juice. GSP was tried both roasted 180°C x 10 minutes and unroasted, while contact time was set at one hour and two hours for comparison. GSP was tried first on four different heat-unstable wines in small-scale experiments. The results showed that GSP removed PR proteins and permitted to achieve heat stability (NTU<2) but with high doses (25-32 g/L) of addition. A similar reduction of PR proteins was obtained in all the wines after 1-h contact time with unroasted GSP as wells as with roasted GSP, which suggests that roasting did not substantially alter the protein-binding capability of GSP. Contact time (1 or 2 hours) did not change the efficacy of protein removal suggesting that the reaction between grape tannins and proteins occurs within one hour. Treated wines showed changes in the matrix composition, with increased phenolic contents (A280) and improved yellow color (CIELAB b* parameter). As for the experiments with grape juice, GSP was added in two juices before fermentation to observe the impact on the composition of the finished wines. Roasted GSP was chosen as the fining agent and the contact time was 1 hour. A lower amount of GSP (5 g/L) was observed to be needed to heat-stabilize (NTU<2) the juices. The corresponding wines showed minor changes in the matrix composition, perhaps because of phenolic-protein interaction and precipitation during the fermentation or degradation via non-enzymatic processes. These results suggested that GSP may be a viable alternative to bentonite. Furthermore, being a by-product of winemaking, GSP utilization would improve the environmental sustainability of winemaking processes.