Uruguayan Study Finds Tannat Wines With 76% Less Sulfites Match Traditional Taste

A new study from Uruguay has examined ways to reduce or replace sulfur dioxide (SO₂) in the production of Tannat wine, a grape variety closely associated with the country. The research, conducted during the 2023 vintage in Canelones, Uruguay, focused on using chitosan and lysozyme as alternatives to traditional sulfite additions. The goal was to maintain microbial stability and wine quality while addressing growing consumer demand for wines with lower sulfite content due to health concerns.

The experiment involved five different winemaking treatments: a traditional method using 125 mg/L SO₂, a reduced-sulfite approach with 30 mg/L SO₂, chitosan at 100 mg/L, a combination of reduced sulfites and chitosan, and a combination of reduced sulfites with lysozyme at 5 mg/L. Each treatment was performed in triplicate using Tannat grapes harvested at technological maturity.

Researchers found that all treatments allowed alcoholic fermentation to proceed normally, with no significant differences in fermentation kinetics or ethanol production. However, the various approaches had marked effects on the microbial populations present during and after fermentation. Wines made with traditional or reduced sulfite levels showed lower counts of lactic acid bacteria (LAB) after bottling, while those treated with chitosan or lysozyme maintained higher LAB populations. Metagenomic analysis revealed that chitosan fostered a more diverse bacterial community, while lysozyme selectively reduced Oenococcus spp., a key LAB involved in malolactic fermentation.

The study also found that reducing SO₂ led to changes in the wine’s chemical composition. Wines with less SO₂ had lower concentrations of phenolic compounds such as anthocyanins and tannins. This was attributed both to increased oxidation—since SO₂ acts as an antioxidant—and to direct interactions between chitosan or lysozyme and phenolic compounds, which can cause them to precipitate out of the wine. These chemical changes affected the color of the wines: low-sulfite treatments tended to be lighter and less saturated in color compared to those made by traditional methods.

Despite these measurable differences in chemistry and microbiology, sensory analysis by a panel of experienced tasters found no significant differences in overall preference among the wines. The only attributes that varied significantly were persistence (with traditional wines scoring highest) and bitterness (perceived as greater in traditional and chitosan-only wines). Other characteristics such as color intensity, aromatic quality, acidity, and astringency were rated similarly across all treatments.

The findings suggest that it is possible to reduce or replace SO₂ in Tannat winemaking without compromising sensory acceptability, but careful management is required. Lowering sulfite levels changes the balance of microbial populations and makes phenolic compounds more vulnerable to oxidation or removal by additives like chitosan and lysozyme. This can affect both the stability and appearance of the wine.

The choice between chitosan and lysozyme as alternatives depends on specific winemaking goals. Chitosan encourages a more complex but less predictable microbiota, while lysozyme offers targeted control over LAB populations. Both require attention to process management to ensure that microbial stability is maintained and that phenolic structure—and thus color and mouthfeel—are preserved.

This research responds to international trends toward lower-sulfite wines and aligns with evolving regulations from organizations such as the International Organization of Vine and Wine (OIV), which has encouraged reductions in permitted SO₂ levels over recent years. The study was supported by Uruguay’s National Agency for Research and Innovation (ANII) and involved collaboration between academic researchers and local wineries.

As consumer interest in natural and low-intervention wines continues to grow, studies like this provide important data for winemakers seeking to balance safety, quality, and market demand. The results indicate that alternative antimicrobial strategies can be viable but must be carefully tailored to each wine’s needs to avoid unintended changes in composition or sensory character.