Nowadays, the use of sulfur dioxide (SO₂) during the winemaking process is a controversial societal issue. In order to reduce its use, various alternatives are emerging, in particular bioprotection by adding yeasts, with different impacts on yeast microbiota in early winemaking stages. In this study, quantitative-PCR and metabarcoding high-throughput sequencing (HTS) were combined with MALDI-TOF-MS to monitor yeast population dynamic and diversity in the early stages of red winemaking process without sulfites and with bioprotection by Torulaspora delbrueckii and Metschnikowia pulcherrima addition. By using standard procedures for yeast protein extraction and a laboratory-specific database of wine yeasts, identification at species level of 95% of the isolates was successfully achieved by MALDI-TOF-MS, thus confirming that it is a promising method for wine yeast identification. The different approaches confirmed the implantation and the niche occupation of bioprotection leading to the decrease of fungal communities (HTS) and Hanseniaspora uvarum cultivable population (MALDI-TOF MS). Yeast and fungi diversity was impacted by stage of maceration and, to a lesser extent, by bioprotection and SO₂, resulting in a modification of the nature and abundance of the operational taxonomic units (OTUs) diversity.

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.

Additives have been used in the food industry for many years, to prevent food spoilage and extend shelf life. These chemical additives are a source of controversy and their use must be reduced in the face of societal demand. In enology, this applies in particular to sulfur dioxide (SO2). There has been recent research on bioprotection as an alternative to sulfite addition in the pre-fermentation phase. This technical article discusses the many advantages of using bioprotection agents.