Due to climate change, we are facing increasingly long periods of drought, which can have a negative impact on the quality of grapes and wine of the grapevine (Vitis vinifera L.). In 2021, we tested the effectiveness of kaolin on the variety 'Refošk' and its effect on reducing drought stress and the impact on the quality of grapes and wine. The experiment was conducted in Baredi, Slovenia. We were particularly interested in the effect of kaolin treatment on the content of secondary metabolites in grapes and consequently in wine. Kaolin was applied to the vines three times: on July 31 (30 g/L), on August 14 (20 g/L), and on August 28 (20 g/L). The trial included 25 vines treated with kaolin and 25 vines representing the control plot. The trial was conducted in 10 blocks, five control blocks and five kaolin treated blocks. At the time of technological maturity, we harvested the grapes and took them to the cellar. In the cellar we separated the berries from the stems, squeezed them and performed the first analyses. The process of microvinification took place for 24 days at 18 °C. We monitored the fermentation process daily and soaked the berry skins. After maceration, we poured off the wine and left it to ferment until the end. After fermentation, the wine was sulfurized and bottled while the final analyses were performed. The analyses were performed with the WineScanTM, a spectrophotometer and HPLC. After statistical analysis of the data, we found no statistically significant differences between the control samples and the samples treated with kaolin, in terms of the content of total sugars, total acids, phenolic compounds and other parameters studied in the grapes. There were also no statistically significant differences in the parameters measured in the control wine and the wine treated with kaolin. Therefore, we conclude that kaolin has no negative effects on the quality of grapes and wine.
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