Bioprotection Emerges As Natural Alternative To Reduce Sulphur Dioxide In Winemaking

A natural approach to protection

The case for bioprotection is based on its role as a natural alternative to reduce or eliminate chemical additives and was inspired by the agri-food industry. Bioprotection uses microorganisms or their metabolites to inhibit or eliminate unwanted microorganisms in food, thereby ensuring product hygiene and extending shelf life without compromising sensory properties.^1,2

The OIV definition

The OIV (International Organisation of Vine and Wine) defines bioprotection as follows: “Use of oenological microorganisms, by direct effect or through some derivatives (zymocins, bacteriocins…) produced by the inoculated protective microorganisms and not added as purified products, to control the development of other undesirable microorganisms and/or to avoid oxidations, to reduce SO₂ use in grapes and wines and to preserve the sensory properties of the final product.”³

According to the OIV, bioprotective yeast in oenology must be effective against specific spoilage microorganisms under conditions typical of the early stages of winemaking.

Why winemakers turn to bioprotection

During the pre-fermentative stage of winemaking, before Saccharomyces cerevisiae becomes dominant, there is a high risk of microbial spoilage.⁴ This critical phase is traditionally managed by the addition of sulfur dioxide (SO₂). However, due to various factors, new alternatives to SO₂ as a preservative in winemaking are emerging, such as bioprotection via the addition of non-Saccharomyces yeasts.

Non-Saccharomyces yeasts were once considered undesirable due to their association with sluggish or stuck fermentations and the production of off-flavours that could lead to financial losses.⁵ However, perceptions have shifted in recent decades, and today several non-Saccharomyces species are commercially available as Active Dry Yeast (ADY) and are increasingly used for their beneficial properties. While some non-Saccharomyces yeasts enhance wine sensory properties, others can help protect against spoilage. They can help suppress the growth of unwanted microorganisms by rapidly colonising the must. Although not primarily involved in alcoholic fermentation, their presence plays a valuable role in stabilising the microbial environment at a critical point in the process.

The use of bioprotective yeasts supports a broader shift in the wine industry towards reducing dependence on chemical additives.⁶ The growing consumer pressure to reduce sulfite use has prompted wine producers to explore alternative preservation methods. Other factors driving the adoption of bioprotection include the effects of climate change, such as increased juice pH, as well as regulations on maximum SO₂ levels and additive labelling requirements.

Unpacking SO₂

Sulfur dioxide is one of the most widely used additives in winemaking.⁴ It can be added at various strategic stages: in juice, after fermentation (both alcoholic and malolactic), during wine ageing and at bottling. It possesses three main properties:

• Antimicrobial – In juice, SO₂ inhibits the growth of unwanted microorganisms, favouring the colonisation of the medium by yeasts of the Saccharomyces cerevisiae species, which are more tolerant to SO₂.
• Antioxidant – SO₂ limits chemical oxidation, thereby preserving aroma and colour, limiting browning, and protecting sensitive compounds such as varietal thiols.
• Antioxidasic – SO₂ inhibits enzymes such as grape tyrosinase and, to a lesser extent, Botrytis laccase, which are responsible for the enzymatic oxidation of phenolic compounds.

Because of these three main traits, SO₂ is regarded by many winemakers as an essential tool during both the pre-fermentative and storage phases of winemaking to prevent spoilage and ensure wine quality.

Regulatory pressure on SO₂ use

Despite its benefits, high doses of SO₂ can cause health issues in sensitive individuals.^4,6 Therefore, the World Health Organisation (WHO) promotes the use of alternative methods to lessen or eliminate the use of SO₂ in wine production. Legislation has also evolved in recent years, lowering the permitted SO₂ concentrations in wine. Additionally, sulfites must be indicated on wine labels if the concentration exceeds 10 mg/L of SO₂.

Climate change and the pH problem

Another obstacle for SO₂ is the impact of climate change on the pH of juice and wine, and therefore the antimicrobial properties of SO₂.⁷ Due to global warming, pH levels have increased in recent years. The higher the pH of a juice or wine, the smaller the proportion of SO₂ in its molecular form, which is the form that protects the juice and the wine from microbial spoilage and off-flavour formation. Juices and wines with pH values below 3.5 are generally less susceptible to microbial spoilage. Conversely, juices and wines with pH levels near 4 are particularly risky, as many spoilage bacteria and yeasts can easily develop during winemaking.

Unlike SO₂, bioprotection is unaffected by pH and can protect juice in which SO₂ has a limited antimicrobial effect due to high pH. A complementary action to bioprotection is bioacidification by selected yeasts during fermentation, which lowers the pH and thereby enhances the antimicrobial effectiveness of SO₂ in the final wine.^8,9

Mandatory labelling and consumer perception

The European Commission’s mandatory labelling of nutritional and ingredient information for wine is likely to cause confusion and doubt among consumers, thereby undermining wine’s reputation as a natural product.¹⁰ This provides wineries with an opportunity to adopt clear labelling practices by avoiding additives that require labelling.

According to the regulation, additives used in wine production must be listed. Yeasts used in wine production are considered processing aids and therefore do not require listing.¹¹ Yeast derivatives that serve specific functions in wine production are also regarded as processing aids and are exempted accordingly. The only yeast compound that must be listed as an ingredient is yeast mannoproteins, as it is considered a “stabiliser” and thus an additive. Therefore, using bioprotective yeasts in no-sulfur-added winemaking can help create clean-label wines. The same applies to using bioacidification yeasts rather than adding exogenous tartaric acid to control wine acidity and pH.

Supporting sustainability and microbial diversity

The growing concern over the environmental impact and economic sustainability of wine production has led many wine producers in recent years to adopt sustainable grape-growing and winemaking practices.¹² Using bioprotective yeasts during the pre-fermentative stage can help protect the must from oxidation and spoilage, mitigating economic losses. It may also enhance microbial biodiversity by preventing the dominance of Hanseniaspora uvarum.¹³ This spoilage yeast can produce high levels of acetic acid and ethyl acetate during the early stages of fermentation.⁷

Concluding remarks

Bioprotection provides a practical, science-based solution for a sector facing tighter regulations, evolving consumer expectations, and growing challenges related to climate change. It reduces dependence on SO₂ at a time when its effectiveness and social acceptance are under scrutiny. It stabilises musts when they are most vulnerable and preserves aromatic potential.

Taken together, bioprotection in the pre-fermentative stage and bioacidification during fermentation form a robust strategy. LAFFORT® provides two solutions for bioprotection (Table 1) and two solutions for bioacidification (Table 2). For many wineries, bioprotection and bioacidification are no longer experimental; they are practical tools that enhance cellar resilience in a changing world.

References

1. Lücke, F.K. Utilization of microbes to process and preserve meat. Meat Sci. 2000;56:105-115.
2. Windholtz, S., Nioi, C., Thibon, C., Bécquet, S., Vinsonneau, E., Coulon, J. & Masneuf-Pomarède, I. Bioprotection as an alternative to SO₂ in the pre-fermentation phase. IVES Tech Rev. 2023.
3. Oelofse, A., Capece, A., Morata, A., Von Wallbrunn, C., Baldeschi, G. et al. Use of bioprotection strains in winemaking. OIV Collective Expertise Document. 2024.
4. Escribano-Viana, R., González-Arenzana, L., Garijo, P., Fernández, L., López, R., Santamaría, P. & Gutiérrez, A.R. Bioprotective effect of a Torulaspora delbrueckii Lachancea thermotolerans mixed inoculum in red winemaking. Fermentation. 2022;8(7):337.
5. Puyo, M., Simonin, S., Bach, B., Klein, G., Alexandre, H. & Tourdot-Maréchal, R. Bio-protection in oenology by Metschnikowia pulcherrima from field results to scientific inquiry. Front Microbiol. 2023;14:1252973.
6. Di Gianvito, P., Englezos, V., Rantsiou, K. & Cocolin, L. Bioprotection strategies in winemaking. Int J Food Microbiol. 2022;364:109532.
7. Morata, A., Loira, I., González, C. & Escott, C. Non-Saccharomyces as biotools to control the production of off-flavors in wines. Molecules. 2021;26(15):4571.
8. Hranilovic, A., Gambetta, J.M., Schmidtke, L. et al. Oenological traits of Lachancea thermotolerans show signs of domestication and allopatric differentiation. Sci Rep. 2018;8(1):1-13. doi:10.1038/s41598-018-33105-7.
9. Vion, C., Muro, M., Bernard, M. et al. New malic acid producer strains of Saccharomyces cerevisiae for preserving wine acidity during alcoholic fermentation. Food Microbiol. 2023;112:104209. doi:10.1016/j.fm.2022.104209.
10. Pabst, E., Szolnoki, G. & Mueller Loose, S. How will mandatory nutrition and ingredient labelling affect the wine industry? A quantitative study of producers’ perspectives. Wine Econ Policy. 2019;8(2):103-113. doi:10.14601/web-8084.
11. International Organisation of Vine and Wine. Additives, Processing aids, Contaminants. Available from: https://www.oiv.int/standards/international-code-of-oenological-practices/part-0/additives%2C-processing-aids%2C-contaminants.
12. Nardi, T. Microbial resources as a tool for enhancing sustainability in winemaking. Microorganisms. 2020;8(4):507.
13. Windholtz, S., Dutilh, L., Lucas, M., Maupeu, J., Vallet-Courbin, A., Farris, L., Coulon, J. & Masneuf-Pomarède, I. Population dynamics and yeast diversity in early winemaking stages without sulfites revealed by three complementary approaches. Appl Sci. 2021;11(6):2494.

For more information, contact Karien O’Kennedy

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