Microbial changes during malolactic fermentation in red wine elaboration

Winemaking is based on complex microbial interactions. They result in alcoholic and malolactic fermentation. In some cases undesirable micro-organisms pass beyond a limit and become prejudicial to wine quality. It is particularly the case of Brettanomyces bruxellensis which produces volatile phenols. Most of wine microbial studies have been focused on only one species and that can lead to incomplete and biased results by neglecting possible interactions between the populations. The aim of this study was to obtain a global survey of wine microflora and its quantitative and qualitative changes during the malolactic fermentation, the last microbial intervention before sulphur dioxide addition. The results were obtained by chemical wine analysis, conventional microbiological methods and molecular tools for microbial identification (PCR-ITS-RFLP, PCR-DGGE). In this study, conducted under cellar scale conditions, several oenological parameters were considered: two different cellars, three grape varieties, MLF in tank or in barrels, use of malolactic starters or indigenous flora. Interactions appeared, mainly between Oenococcus oeni and B. bruxellensis, but also between O. oeni strains. Some explanations are suggested and further investigations are proposed.