Combining high-power ultrasound and oenological enzymes during winemaking for improving red wine chromatic characteristics

Abstract

The use of high-power ultrasound (US) is proving of great interest to the oenological industry due to its effects in the improvement of wine organoleptic characteristics, especially in terms of color [1, 2]. Even though the International Organization of Vine and Wine approved its industrial use on crushed grapes to favor the extraction of phenolic and aroma compounds during winemaking [3], most of the published studies have generally been carried out at a laboratory scale being very scarce the studies on a semi-industrial and industrial scale [2]. The effect of US, due to cavitation phenomenon, is the developing of shock waves capable of breaking solid surfaces such as cell walls of grape skins and seeds, improving the extraction of those compounds located inside the cells, mainly phenolic compounds. This effect sought with the use of US is similar to that observed when maceration enzymes (E), mainly pectolytic enzymes, are used with the purpose of dissembling the cell wall structure [1]. The combination of both techniques could be a useful tool for improving wine phenolic content if a synergistic effect occurs [1]. The objective of this study is to determine on a semi-industrial scale if the combined use of the US and E at the beginning of the maceration process enhance the effect of both techniques and if the ripening stage of the grapes affects the output of the results, since this factor has been found to interfere with the effect of the enzyme [4].Thereby, pilot scale trials were carried out with Monastrell grapes at two different ripening levels, testing two different maceration times (72 hours and 7 days) at the winery. Vinifications were carried out using both techniques (E and US) separately as well as in combination, also testing if the moment of the enzyme addition (prior to the application of US or added after the grapes had been sonicated) led to differences in the final wine quality. A semi-industrial scale high power ultrasound equipment was used at a sonication frequency of 30kHz. Physicochemical and chromatic parameters by spectrophotometry and high-performance liquid chromatography were analyzed at the time of bottling.The results obtained showed differences depending on the moment of the enzyme addition. When the enzyme was added after the sonication of the crushed grapes, the wine obtained with the less ripen grapes and a 72 hours maceration time presented chromatic characteristics similar to the control wine with 7 days of skin maceration. The effect was much more evident when the same experiment was carried out with the more mature grapes.In conclusion, this study on a semi-industrial scale demonstrated that an adequate combination of these techniques entails an optimization of the maceration process not only in time but also in improving the organoleptic characteristics in wine, the results being of special industrial interest.