Influence of sulphur dioxide management on microbial populations during wine ageing

The use of food preservatives is controversial these days, and sulphur dioxide (SO2) is no exception. Microbial communities have been studied particularly during the prefermentative and fermentative stages in the absence of added SO2. However, the microbial risks associated with the reduction or absence of SO2, particularly during the wine ageing process, have been little studied. The microbiological control of wine ageing is a key issue for winemakers wishing to produce high-quality wines without added SO2. The present study aims to evaluate the impact of different wine ageing strategies, depending on whether or not SO2 is added, on microbial population levels and diversity. Sulphite management had minimal impact on the population levels of yeast and acetic acid bacteria. Conversely, the population of lactic acid bacteria, whether from inoculation or spontaneous malolactic fermentation (MLF), was significantly impacted by SO2 management. High and stable population levels of around 105 CFU/mL were observed in the SO2-free modalities. Sulphiting after malolactic fermentation has a greater effect on lactic acid bacteria up to four months of ageing than standard SO2 addition at the time of vatting. Oenococcus oeni was the only species detected during ageing using a culturable approach. After five months of ageing, a high genetic diversity of Oenococcus oeni was highlighted in all modalities, even in the inoculated one with a commercial strain. The high population level of Oenococcus oeni was associated with acetic acid and D-lactic acid production, as well as mousy off-flavours. One sulfite treatment at the end of MLF inhibits the growth of Oenococcus oeni, but only temporarily. Winemakers should consider the stage and number of treatments to limit the development of lactic acid bacteria (LAB) during ageing and preserve the quality of red wine.