WINETECH Technical Yearbook 2020

INTRODUCTION Bentonite is widely used during winemak- ing to remove haze-forming proteins in white and rosé wines, however, the appli - cation has some significant disadvantages. These include: ● Poor settling resulting in significant wine volume losses. ● Potential changes in wine sensory composition. ● Sustainability of the product (non- renewable). ● Environmental impact of bentonite waste. Research institutions are constantly on the lookout for possible alternatives of which chitosan and proctase have been identified as viable options (Colangelo et al ., 2018; Robin- son et al ., 2012). The goal is to find a sustain - able and economical product that preserves the wine quality, while efficiently remo­ ving the haze-forming proteins. Researchers looked to winery waste for the treatment of heat-unstable wines and conducted a pre- liminary study assessing the feasibility of grape seed powder as a novel and sustainable bentonite alternative (Romanini et al. , 2020). Some of the main findings in this study will be reported in this article. MATERIALS AND METHODS Grape seed powder (GSP) was added to Australian Sauvignon blanc juice and wine

to test the effect of the additive on the heat stability of the wine. The study also included wines from other white grape varieties, however, for these, the effect of the addition of GSP to the juice was not investigated. Further, similar results were obtained for the wines made from different cultivars. The Sauvignon blanc juice and wine were f ined wi th GSP isolated from unfermented frozen Chardonnay grape marc. The seeds were either processed raw or it was roasted prior to refinement. The ref ined product was added to the juice and wine at 20°C at various dosages. The GSP was in contact with the medium by stirring for either one or two hours before it was removed by centrifugation and filtration. The juice was then fermented and wine filtered for analyses. A sample was also fined with 0.5 g/L bentonite for comparison. Heat stability tests (McRae et al ., 2018) were performed on the juice and wine before the addition of GSP and after the removal thereof. The sample was filtered and heated to 80°C for two hours and cooled to room temperature for three hours. The turbidity of the sample was measured using a turbidity meter before heating and after cooling and a difference of less than two nephelometric turbidity units (NTU) was considered stable.

New developments in protein stability

DECEMBER 2020

CARIEN COETZEE: Basic Wine, Stellenbosch KEYWORDS: Protein stabilisation, bentonite alternatives

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