Application of high power ultrasounds during red wine vinification

Abstract

Wine color is one of the main organoleptic characteristics influencing its quality. It is of especial interest in red vinifications due to the economic resources that wineries have to invest for the extraction of the phenolic compounds responsible of wine color, compounds that are mainly located inside the skin cell vacuoles. Moreover, these phenolic compounds not only influence color but also other organoleptic properties such as body, mouthfeel, astringency and flavour. The transference of phenolic compounds from grapes to must during vinification is closely related with the type of grapes and the winemaking technique. During traditional winemaking, grapes are crushed and skin macerated for several days, with pumps over to facilitate the color extraction. To increase this extraction, some chemical (maceration enzymes) or physical technologies (thermovinification, criomaceration, flash-expansion) can be applied. In this work, a new methodology has being tested. This methodology consists in the application of high power ultrasounds to crushed grapes to increase the extraction of phenolic compounds. Ultrasound is a non-thermal processing method, which is already widely used in the food industry due to its mild application but significant effects on the product. The mechanical activity of the ultrasound breaks the cell wall mechanically by the cavitation shear forces, and facilitates the transfer of phenolic and other compounds from the cell into the must. Also, the particle size reduction by the ultrasonic cavitation increases the surface area in contact between the solid and the liquid phase. High power ultrasounds have been used in the vinification of Monastrell grapes. Crushed grapes were treated with ultrasound, considering as variables the time the ultrasounds were applied to the crushed grapes (two different times were applied) and the duration of the fermentative skin maceration period (3, 6 or 8 days) and the results were compared with a control vinification, where grapes were not subjected to any treatment and were skin macerated during 8 days. The wine chromatic characteristics (determined spectrophotometrically) and the individual phenolic compounds (anthocyanins and tannins, determined by HPLC) were followed during all the maceration period, at the end of alcoholic fermentation and after three months in bottle. The wines made with ultrasound treated grapes presented differences with control wine, especially as regard total phenol content and tannin content, the wines with three days of maceration time presenting similar concentration of anthocyanins and twice the concentration of tannins than control wines with 8 days of maceration time. Other possible advantages of wines made with ultrasound treated grapes will be discussed.