We knew them to be formidable… But some are appalling! At least that is the reaction one can have when discovering some of the results of the Chitowine project unveiled at the start of 2021, concerning alteration yeasts. Brettanomyces bruxellensis.
Presented by Julie Maupeu, Microflora laboratory manager, transfer unit of the Oenology Research Unit of ISVV Bordeaux, and Marguerite Dols-Lafargue, teacher-researcher at the Polytechnic Institute of Bordeaux, the study reveals a major result: “13% of strains Brettanomyces bruxellensis of our study, are resistant to chitosan “ Julie Maupeu announces.
“ 13% of strains Brettanomyces bruxellensis of our study, are resistant to chitosan “
At the laboratory scale, Julie Maupeu and Marguerite Dols-Lafargue have tested more than 50 strains of Brettanomyces bruxellensis on a Bordeaux finished red wine voluntarily contaminated with 103 Bretts cells / mL, “A consistent population is found in the cellar in contaminated red wines” adds Julie Maupeu.
They added between 4 and 10 g / hl (maximum authorized dose) of chitosan, leaving it in contact for three and ten days. “We then racked the wine to analyze it and compare it to the control that had no treatment with chitosan. The islands were also checked ” she continues. “Often, we find chitosan in formulation, with enzymes or inactive yeasts. In our study, we used it pure ”.
Three different behaviors
“41% of the strains studied responded well to the treatment. Their population has clearly decreased or even disappeared in the wine racked as well as in the lees. 46% had an intermediary behavior. In 30% of these wines, we found strains of Brettanomyces bruxellensis still viable. It was also left on the lees on almost all samples. And the remaining 13% of Bretts were totally resistant to chitosan with a population after treatment identical to the initial population ” dtaille the person in charge.
The variation in the dose between 4 and 10 g / hL of chitosan had no impact on the intermediate and resistant strains. To go further, the research teams investigated whether there was a relationship between a strain’s response to chitosan and its membership in a genetic group. “For the moment, we have not been able to identify a genetic group of Brettanomyces bruxellensis which are tolerant or not to chitosan, as is the case for strains tolerant or not to SO2 ” explains Julie Maupeu.
Two other results
Julie Maupeu emphasizes the value of drawing off the treated wine, after 3 or even 10 days of contact, if the treatment with chitosan is curative. “We found that the remaining strains in the lees after treatment were able to produce volatile phenols and produced them on our samples left on the lees. As a preventive measure, the chitosan present in the lees will be effective in combating the implantation of sensitive strains only, which could develop, even beyond 3 months ” explains the manager.
Another result of the study: the pH, the temperature of the wine and the alcohol content have no influence on the effectiveness of a treatment with chitosan to eliminate Brettanomyces bruxellensis. “This effectiveness depends above all on the nature of the strains of B. bruxellensis present in the wine. Other elements of the wine could nevertheless modulate the effectiveness of the treatment ” adds Julie Maupeu, without saying more.
A glimmer of hope
Despite the absence of a genetic link concerning resistance to chitosan between the different strains studied, it seems that the strains of Sulphite tolerant Brettanomyces bruxellensis are predominantly sensitive to chitosan. “That’s pretty good news! “ points out Julie Maupeu. “In the future, we would like to develop a test to predict the effectiveness of the treatment with chitosan in wine” adds the manager, who specifies that the Chitowine project is coming to an end. Full results should be available in early 2022.