Study Finds Low-Dose Mannoproteins Speed Malolactic Fermentation in Tempranillo

A study published Thursday in OENO One found that adding selected mannoprotein extracts to red wine helped speed up malolactic fermentation in Tempranillo wines from two consecutive harvests, while also changing parts of the wine’s color-related phenolic profile without raising volatile acidity or altering pH in a harmful way.

The research was carried out by Paloma Toraño, Albert Bordons, Nicolas Rozès, and Cristina Reguant using Tempranillo wines from the 2022 and 2023 vintages made at the experimental winery Mas dels Frares of Universitat Rovira i Virgili in Tarragona, Spain. The team studied how commercial mannoprotein extracts affected malolactic fermentation driven by Oenococcus oeni PSU-1, a lactic acid bacterium widely used as a reference strain in wine research.

Malolactic fermentation is a key step after alcoholic fermentation in many red wines. In that phase, bacteria convert L-malic acid into L-lactic acid, which lowers sharp acidity and helps improve microbiological stability. But the process can be slow or stop altogether because wine is a difficult environment for bacteria, with alcohol, acidity, and other stress factors limiting their activity. The authors said that uncertainty is one reason winemakers are interested in tools that can make the process more reliable.

The researchers tested three commercial mannoprotein products derived from Saccharomyces cerevisiae cell walls. These extracts differed in their polysaccharide and protein composition, which the team said matters because those structural differences can affect how the compounds interact with wine and with microorganisms. Mannoproteins are already known to occur naturally in wine through fermentation and yeast breakdown, but their amount and characteristics vary with yeast strain and cellar practices.

The trials were done in real wine, not just in synthetic media. That is an important point because much of the earlier work in this area was done under more simplified laboratory conditions. The wines from the two harvests were chemically similar before malolactic fermentation began. In 2022, the wine had a pH of 3.55, alcohol of 13.2%, and L-malic acid of 1.62 g/L. In 2023, the wine had a pH of 3.51, alcohol of 13.8%, and L-malic acid of 1.61 g/L.

In the 2022 vintage, the team added mannoproteins at 2 g/L. Wines treated with the three extracts completed malolactic fermentation in 14 days, while the untreated control needed 17 days. The paper said that difference was statistically significant. The authors also noted that by day 12, treated wines had already finished the process, while the control still had more than 0.2 g/L of L-malic acid left.

In the 2023 vintage, the researchers shifted to lower doses that were closer to practical cellar use, testing 0.25 g/L and 0.50 g/L. According to the study, those lower additions still shortened fermentation. Depending on the extract and dose, treated wines completed malolactic fermentation in about 11 to 12 days, compared with 14 days for the control. The paper’s abstract highlighted 0.25 g/L as an effective low dose for stimulating the process.

The study did not find that mannoprotein addition increased the population of O. oeni in an obvious way by the end of fermentation. The bacterial counts remained around 10^6 CFU/mL across treatments. That suggests the benefit was not simply a matter of larger final cell numbers. The authors said the improved fermentation kinetics could be linked to mannoprotein consumption by O. oeni, meaning the added compounds may have served as a useful resource during the bacteria’s metabolic activity.

The wine quality results were more mixed, but still notable. The researchers reported no negative effect on pH or volatile acidity, two parameters that are important for both stability and sensory quality. At the same time, mannoprotein addition changed the phenolic composition. Total anthocyanins fell, but stable acylated anthocyanins and vitisins increased. Those compounds are linked to more stable color in red wines, suggesting that the additives may reshape the pigment system rather than simply preserve all pigments at the same level.

That outcome may matter for wineries because malolactic fermentation is not only a technical step but also a scheduling and stability issue. If a low-dose additive can make the process finish sooner and more consistently from one vintage to the next, it could help with cellar planning, microbiological control, and the management of wine color during aging. The study does not show a guaranteed commercial outcome, but it points to a practical route that producers may be able to test under normal winemaking conditions.

The authors also stressed that the wines used in the trials were not especially harsh for O. oeni. Their pH was above 3.5, alcohol levels were moderate for red wine, and other conditions were relatively favorable. Because of that, the gains in fermentation time were modest rather than dramatic. Even so, the team said the results are relevant because they show that the effect can be detected clearly in real wine and at doses that are more realistic for winery use.

The work also adds to a broader effort to understand why some mannoprotein products perform differently from others. In this study, the three extracts had distinct protein and polysaccharide profiles. One had very high polysaccharide content and low protein, while the others contained more protein and different molecular-weight fractions. The paper argues that these chemical differences help explain variations in how the extracts influence bacterial metabolism and wine composition.

The authors carried out the experiments in triplicate and used statistical analysis including ANOVA and Tukey’s test with significance set at p<0.05. They said their findings support the use of specific mannoprotein extracts as a way to stimulate malolactic fermentation in red wine and to influence pigment composition at the same time, particularly when used at low doses that are feasible in a commercial cellar.