High-power ultrasound for improving chromatic characteristics in wines. Does a varietal effect exist?

Abstract

The use of high-power ultrasound (US) during the winemaking process has been extensively studied at laboratory scale in order to demonstrate its possible use to improve the extraction of compounds of interest. However, studies on semi-industrial and industrial scale are needed to confirm this positive effect, since the International Organization of Vine and Wine approved its industrial use in 2019 [1]. On the other hand, numerous studies on the characterization of grape varieties have shown some differences in their physical and chemical characteristics [2], and these may affect the outcome of the ultrasound treatment. Thus, our work focuses on the chromatic study of wines made from three different varieties (Monastrell, Cabernet Sauvignon and Syrah), to determine whether the use of US at a semi-industrial level facilitate the extraction of compounds of interest from the different varieties.Thereby, Monastrell, Syrah and Cabernet Sauvignon grapes were vinified. Four pilot scale trials were carried out for each variety: In two of them, ultrasound treatment was not applied in order to be used as controls (C). For the other two elaborations, the destemmed and crushed grape was subjected to ultrasound treatment (US) using a semi-industrial scale high power ultrasound equipment at a sonication frequency of 30kHz and a flow rate of 400 kg/h. Sonication was applied after destemming-crushing of the grapes for subsequent maceration. One of the control trials along with one of the US trials underwent a 3-day maceration, while the remaining two trials underwent a 7-day maceration of must-wine contact with the solid parts of the grapes. Physicochemical and chromatic parameters, as well as phenolic concentration and composition were analyzed by spectrophotometry and high-performance liquid chromatography respectively at the time of bottling.The results showed large differences between varieties. Wines obtained by sonicated grape of Syrah and Cabernet Sauvignon varieties showed greater color intensity and concentration of the different phenolic compounds analyzed both with 3 or 7 days of skin maceration. Moreover, those wines made from sonicated grapes and 3 days of skin maceration present similar chromatic characteristics of those wines made from control grapes and 7 days of maceration, which indicates that ultrasounds used on a semi-industrial scale can be of great interest in order to reduce maceration time in wineries, thus increasing their production capacity.Different behavior was observed in Monastrell wines, where no positive effect was observed in wines made from sonicated grapes and 3 days of maceration although wines obtained from Monastrell sonicated musts and 7 days of skin maceration showed a higher concentration of polymerized stable compounds and tannins than their respective controls, which would be of interest to improve the long-term stability of these wines. The possible reasons behind these differences would be discussed.

References

[1] OIV. (2019). Resolution OIV-OENO 616-2019. Paris, France: OIV.
[2] Ortega-Regules, A., Ros-García, J. M., Bautista-Ortín, A. B., López-Roca, J. M., & Gómez-Plaza, E. (2007). European Food Research and Technology, 227(1), 223–231.