| The north slope of Tianshan Mountains in Xinjiang is one of the major wine regions in China, and Cabernet Sauvignon is the main wine grape variety in this region. Lack of fruit note and elegance in aroma, poor color stability are main problems for wines from this region as many other Cabernet Sauvignon wines from western China. To improve the overall wine quality in this region, a series of vineyard management and winemaking experiments were conducted by us in recent years. The works showed in this dissertation were parts of the researches, and were focused on the influence of pre-fermentation technologies, such as cold maceration and grape sorting, on wine aroma.All the researches in this dissertation were based on industrial winemaking. The pre-fermentative cold maceration treatment (CM) and grape berry sorting technology were conducted in two successional vintages respectively, and the impacts on wine aroma during fermentation and aging process were studied. Two kinds of industrial scale fermentors, automatic pumping over tank (PO-tank) and automatic pouching down tank (PD-tank), were applied for CM experiment, and two strains of commercial yeasts (L2323, D254) were used for grape sorting experiment. After fermentation, all wines from different treatments were aged in oak barrels for12months, and the aroma compounds were analyzed during the aging process. The CM treated wines (CM-wine) and control wines (Co-wine) were aged both in stainless steel tank and French oak barrels with two toasting degree (light toasted and medium toasted) and grain tightness (tight grain and moderate grain). The results obtained from this study were as follows:The CM treatment had different effect on wine aroma depending on the types of fermentor, more effective for PO-tank than PD-tank. The fruity aroma series were enhanced by the CM treatment in PO-tank fermented wines even after barrel aging. The enhancement of wine aroma by CM treatment was a result of the improvement on some esters (isoamyl acetate, hexyl acetate, ethyl laurate,9-ethyl decenoate, isoamyl lactate, ethyl2-hydroxy-4-methyl pentanoate) and decrease on some fusel alcohols (isobutanol, isopentanol) during fermentation and barrel aging. More hexanol was produced during CM process compared to the Co wines, and punching-down could accelerate this compound in wine.Although the fruity aroma series and some esters were low in berry-selected wines (BS-wine) than cluster-selected wines (CS-wine) at the end of alcoholic fermentation, this difference between BS and CS wines were disappeared at the end of barrel aging due to the rapid degradation of these esters (isoamyl acetate, ethyl decanoate, ethyl octanoate and ethyl laurate). D245was more suitable for making a more fruity wine because of its high production of P-ionone and some esters such as ethyl hexanoate, ethyl octanoate and ethyl decanoate.The toasting degree and grain tightness of oak barrels had some significant impacts on wine odorants derived from fermentation process such as isoamyl acetate, ethyl laurate, ethyl decanoate and isoamyl decanoate. Oak barrels with light toast degree and tight grain were more benefit for the maintenance of these esters and the formation of fruit note during wine aging. |
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