Water insoluble chitosan in the form of powder having a particle size of 5-50 microns, is claimed. Independent claims are included for: (1) a composition comprising the chitosan； and (2) #a method of curative and/or preventive treatment of a food liquid of vegetable origin, such as a food liquid of plant origin prepared by fermentation, where undesirable yeasts are to be eliminated, of which the presence is to be prevented, and/or where the population is to controlled, preferably yeasts of genus Brettanomycesand/or Dekkera, preferably yeasts of B. anomalus, B. bruxellensis, B. claussenii, B. custersianus, B. Lambicus, B. naardenensisand/or B. nanus, comprising placing, in the presence of food liquid with a water insoluble chitosan in powder form of which a particle size is 0.1-200 microns at a concentration of 1-10 g/hl of food liquid to be processed, preferably 2-5 g/hl of food liquid to be processed, the chitosan or the composition. ACTIVITY : Fungicide； Antibacterial. MECHANISM OF ACTION : None given.L'invention concerne un chitosane sous forme de poudre micronisée, son utilisation pour lutter contre certaines levures, comme des Brettanomyces, et une méthode de traitement d'un liquide alimentaire. L'invention concerne en particulier un chitosane insoluble dans l'eau sous forme de poudre micronisée dont la granulométrie est comprise entre 5 et 50 microns, et son utilisation dans le traitement de liquides alimentaires et/ou pour lutter contre Brettanomyces.
