EVALUATING WINEMAKING APPLICATIONS OF ULTRAFILTRATION TECHNOLOGY
Ultrafiltration is a process that fractionates mixtures using semipermeable membranes, primarily on the basis of molecular weight. Depending on the nominal molecular weight cut-off (MWCO) specifications of the membrane, smaller molecules pass through the membrane into the ‘permeate’, while larger molecules are retained and concentrated in the ‘retentate’. This study investigated applications of ultrafiltra-tion technology for enhanced wine quality and profitability. The key objective was to establish to what extent ultrafiltration could be used to manage phenolic compounds (associated with astringency or bitterness) and proteins (associated with haze formation) in white wine. Nevertheless, ultrafiltration was also applied to red wine, despite the removal of anthocyanins and tannins (associated with colour and textural properties) being inherently detrimental to wine quality, so as to better characterise the chemical consequences of membrane filtration. The composition of permeate and retentate derived from pilot-scale fractionation of red and white wine using 10 and 20 kDa membranes, and different permeation rates (50, 80, 90, 95%) was investigated. The alcohol content and pH of permeate and retentate were not significantly different from that of the initial wine, but titratable acidity and macromolecules (proteins, polysaccharides and phenolic compounds, including anthocyanins for red wine) were progressively concentrated in the retentate, as a function of both membrane MWCO and the degree of permeation. Red wine permeates were stripped of much of their essential character, such that they were not considered commercially acceptable; whereas the removal of white wine phenolics demonstrated the potential for ultrafiltration to remediate oxidised or highly phenolic wines. Subsequent trials investigated the addition of retentate to (i) fermenting red grape must, (ii) dealcoholised wine, and (iii) permeate, as a potential strategies for enhancing wine colour stability, flavour intensity and/or mouthfeel properties. Whereas colour enhancements were not apparent, likely due to the inherent effects of dilution, differences in wine flavour and mouthfeel were perceived via sensory profiling using the Rate-All-That-Apply method. Findings will enable the wine industry to make informed decisions regarding the suitability of ultrafiltration technology as an innovative approach to improving wine quality and process efficiency, and therefore profitability.
Issue: OENO Macrowine 2023
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membranes, phenolics, proteins, wine