Winetech Technical Yearbook 2022

retentates showed similar haze-forming protein concentrations after treatment by removing more than 83% of the proteins. As expected, the ultrafiltration of the wine delivered heat stable permeate and heat-unstable retentate. All the treatments (unfiltered, as well as filtered and reconstituted wines) to which no bentonite was added, failed the heat-stability test, and were considered heat unstable. Heat and/or protease treatment of the retentate was thus not successful in delivering heat-stable reconstituted wine. However, these treatments did lower the bentonite requirements. The bentonite requirements of the applicable treatments were determined based on the change in turbidity after conducting heat-stability tests. For the unfiltered wine (UNF-B), the bentonite requirement was 1.0 g/L. Naturally, the bentonite requirement in g/L for the concentrated retentate was much higher than the full volume. However, less bentonite was needed due to the treatment of a smaller volume of wine. For comparison, the bentonite requirement dosage of the retentate samples was converted back to the original volume and calculated as 0.9, 0.4 and 0.28 g/L for F-B, F-HB and F-HPB, respectively. It seems that the concentration of the proteins in the retentate fraction enabled a more efficient and targeted removal of the proteins, thereby reducing the overall bentonite requirement compared to the dosage needed for the unfiltered wine sample. Therefore, even though heat and/or protease treatment could lessen the bentonite requirements, it could not completely eradicate the need for bentonite. This strategy could still serve the winemaker favourably by reducing the amount of bentonite needed to stabilise the wine and by subjecting a smaller volume of wine to additional stabilisation processes. Sensory evaluation and volatile thiol content The quality of the wines was sensorially assessed by an expert panel of eight winemakers. Results showed no significant differences in quality ratings, and no faulty characteristics were reported. However, tasting notes would suggest that treatments F-HP and F-HB exhibited “riper fruit” characteristics and a slight “cooked-fruit” character while lacking “floral” notes when compared to the other treatments. Interestingly, F-HPB (abundant in desirable fruity and floral aromas) were not considered sensorially similar to F-HP and F-HB and instead closely resembled the wine stabilised via traditional bentonite fining (UNF-B). Bentonite fining did not affect the volatile thiol concentration of the Sauvignon blanc wine. However, ultrafiltration resulted in some decreases in thiol content. The 3MH concentrations were, on average, between 1 500 ng/L and 2 000 ng/L for all the treatments. Ultrafiltration resulted in a 12 - 15% decrease

in 3MH concentration. However, it is uncertain whether these decreases would be sensorially perceived. 3MHA concentrations averaged between 20 and 50 ng/L. These concentrations are relatively low and would likely not have much sensory impact. Ultrafiltration resulted in a 49 - 57% loss in 3MHA concentration which, considering the low starting concentration, might not be sensorially significant. Nonetheless, these decreases could be attributed to polyphenol oxidation during the filtration action, which may have inadvertently caused some aeration and oxidation and will require stringent quality control measures. CONCLUSION Fractionation by ultrafiltration and treatment of the retentate enabled efficient protein stabilisation using less bentonite than traditional fining. This novel method offers a targeted approach of fining only the macromolecule-rich fraction and is likely to reduce the impact on wine quality and sensory properties. ABSTRACT A novel method to obtain a heat-stable wine describes the fractionation of the wine by ultrafiltration and subsequent treatment of the protein-rich retentate. This enabled efficient protein stabilisation using less bentonite than traditional fining and is likely to reduce the impact on wine quality and sensory properties. REFERENCE https://www.wineland.co.za/reducing-bentonite-usage-with-a novel-method-to-obtain-heat-stable-wines/

For more information, contact Carien Coetzee at carien@basicwine.co.za.

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WINETECH TECHNICAL YEARBOOK 2022