Post-harvest high heat treatment on grapes and the effects on wine quality relating compounds
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This research evaluated simulated accumulated summer temperature conditions in grape shipping containers during transportation from vineyard to winery in Texas. Temperature treatments were applied to five batches of destemmed grapes comprised of three batches of red varieties and two batches of white varieties. After 0 to 15 hr treatments, the berries were processed and fermented to wines in micro scale. Phenolic constituents important to wine quality sensory perception, including total phenolics, anthocyanins, tannins and polymeric pigments, as well as color intensity, hue and standard wine parameters were quantified to evaluate the effects of heat at post-harvest stage on the subsequent wines. The results indicate that long distance transportation of berries in Texas may result in high phenolic extraction and elevated browning in white wines, while red wines tended to change red color intensity, tannin concentrations and red pigment profiles, which might not affect red wines sensorily. Heat treatment did not affect pH, titratable acidity, ethanol concentrations, browning, total phenolic concentrations or anthocyanin concentrations compared to the wines made from the low heat treated berries. The composition of phenolic constituents in red wines is relatively stable after the heat treatment before vinification.