A combination of biotechnology tools and coopers elements for an alternative the addition of SO2 at the end of the malolactic fermentation in red wines or at the “mutage” for the “liquoreux” wines

Abstract

In red wines the post-MLF SO2 addition is an essential event. It is also the case for the “mutage” during the elaboration of the “liquoreux”. At these moments SO2 plays an antimicrobial action and an antioxidant effect. But at current pH of wines, ensuring a powerful molecular SO2 has become very difficult. Recent work on Brettanomyces strains have also shown that some strains are resistant up to 1.2 mg / L of molecular SO2. It’s also the case of the some Saccharomuces or Zygosaccharomyces strains suitable to re-ferment “liquoreux” wines after the “mutage”. Biotechnological products are now available for effective antimicrobial actions. Lysozyme inhibits the lactic acid bacteria. Chitosan also acts on the lactic acid bacteria but also efficiently on Brettanomyces. Acid sorbic can be a help to control the development of the undesirable strains yeast strains. On the antioxidant effect oak wood could potentially play a protective role. The development of an electrochemical sensor was used to estimate the influence of different cooperage factors on the antioxydant capacity(CaOx)suitable to be transmit by the wood at the wine. For red wines, during two successive vintages in two different wineries, tests compared classical post-MLF SO2 additions (5 g/hL) in classic new barrels to a treatment with a mixture of lysozyme and chitosan in CaOx optimized barrels. Microbiological monitoring has been done like chemical assays and wines tasted by expert panels. Barrels were also fitted with an innovative device allowing to measure dissolved oxygen without to have to open the barrel. In two different “Sauternes” wineries, test have been done to compare a classic mutage (between 10 and 25 g/hL of SO2) in classic barrels to a half a dose of SO2 and adding a supplement chitosan and sorbic acid in in CaOx optimized barrels. The impact on the microbial flora were investigated as well as the impact on the quality of wine. The innovative device for measuring dissolved oxygen was also used. All these wines were followed until the end of the harvest of breeding, ie on breeding periods of 6-18 months to understand the stability over time of the results. The results show that the test wines are microbiologically more stable than control wines. In the most of the case, always for the wine experiments and often for the “liqoureux”, the dissolved oxygen levels are also lower. Some metabolites (volatile phenols, diacetyl, and acetaldehyde) are less concentrated and colors are more intense and more stable. At the end, the combination of biotechnology tools and CAOX appears of a very efficient has emerged as a very effective technique to reduce the amount of total SO2 in wine as currently requested by consumers and by legislators.