Bioprotection in winemaking

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Reducing sulphur dioxide in winemaking: bioprotection as a sustainable alternative
Isabelle Masneuf-Pomarède — Univ. Bordeaux, Bordeaux INP, Bordeaux Sciences Agro

Sulphur dioxide (SO_₂) has long been a pillar of winemaking practice thanks to its antimicrobial, antioxidant and antioxidase properties. However, winemakers are increasingly being driven to reduce their use for health reasons, regulatory reasons (e.g. organic dry wines) and in response to consumer demands. Among the most promising alternatives, bioprotection — particularly through the use of non-Saccharomyces yeasts — has attracted considerable interest. In the food industry, bioprotection is defined as the use of antagonistic microbial cultures to suppress pathogens and/or extend the shelf life of products, whilst preserving their sensory qualities. In oenology, this strategy relies primarily on species such as Torulaspora delbrueckii and Metschnikowia pulcherrima.

Over the past decade, numerous studies have assessed the effectiveness of bioprotective yeasts as a substitute for SO_₂. Experiments carried out on white and red grape varieties have compared bioprotection (applied at harvest or during the pre-fermentation phase) with the addition of sulphites and untreated controls. Inoculating grape must with non-Saccharomyces yeasts reduces the abundance of filamentous fungi, which are generally associated with a deterioration in the quality of the must. The results regarding the suppression of Hanseniaspora spp., which may contribute to the formation of ethyl acetate and acetic acid, remain inconclusive. The lower efficacy in overripe grapes suggests that bioprotection doses may need to be adjusted according to the ripeness of the grapes. The ability to limit oxidation processes was also studied: some species, such as M. pulcherrima, are highly efficient consumers of O_₂, and this ability may adversely affect acetic acid bacteria during the pre-fermentation phase. However, in the production of dry white wines, this antioxidant capacity of bioprotection has yet to be complemented by an anti-oxidase activity that remains to be developed. Finally, although the use of non-Saccharomyces yeasts for bioprotection effectively preserves and enhances the sensory quality of wines, their co-inoculation with Saccharomyces cerevisiae remains the most efficient strategy for intensifying fruity aromas. Current research highlights the importance of selecting the appropriate yeast species and strains according to winemaking objectives, and of adjusting bioprotection dosages according to grape ripeness and winemaking conditions.

The use of bioprotection as a tool for managing SO_₂
Victor Puente Lopez — Laffort

The steady rise in pH observed in recent years means that the levels of molecular SO_₂ and free SO_₂ in wines are becoming increasingly lower for a given concentration of total sulphurous acid. Given this situation, a loss of microbiological control can lead to an undesirable increase in metabolites such as acetaldehyde, which is the main factor responsible for the rise in combined SO_₂ in wines. Controlling and reducing these levels during the fermentation process is essential for lowering the levels of combined SO_₂. This study presents bioprotection as a tool for reducing the use of SO_₂ in must and grapes, and positions it as a process for controlling acetaldehyde production, presenting results from various applications aimed at controlling the microbial population responsible for contamination during different stages of the fermentation process.

Recordings of the presentations given at Enoforum España 2026 (20–21 May 2026, Zaragoza)