The aim of the study was to test the efficacy of chitosan against the spoilage yeast Brettanomyces bruxellensis.
Researchers from Bordeaux evaluated pure chitosan against 50 strains of Brett as part of a bigger Chitowine project. The project was done on laboratory scale with a Bordeaux red wine that was deliberately contaminated with the different strains. The Brett infected wines were left in contact with the chitosan for 3 – 10 days. Chitosan dosages ranged from 4 – 10 g/hl.
- 41% of the strains reacted well to the treatment by either disappearing completely in both the wine and the lees or by just decreasing substantially.
- 46% had intermediate behaviour in that viable Brett cells could still be detected in the wine and/or the lees.
- 13% of strains were completely resistant in that the Brett population after treatment was exactly the same as the untreated control wine.
- The researchers found no genetic correlation between the resistant strains.
- The temperature, pH or alcohol of the wine did not affect the efficacy of chitosan treatment. Efficacy is determined by the specific strain.
- The study also found that it is mainly the SO2 resistant strains that are sensitive to chitosan.
Significance of the study:
Full results of the Chitowine project will only be available in 2022. However it seems that Brettanomyces shows highly differential behaviour towards treatment and in the absence of knowing what strain one is dealing with, it is best to control Brett with both SO2 and chitosan (and maybe crossflow filtration as well). Suppliers of chitosan often combine the chitosan with other oenological products such as enzymes or inactivated yeasts to enhance its efficacy. It would have been interesting to see what this study’s results would have been if chitosan combined with glucanase enzymes have been used, instead of just pure chitosan.
I therefore would not fall on my sword just yet.