The lower content of organic acids in grape berries due to global warming, and therefore high pHs, is forcing winegrowers to acidify must or wine to preserve their microbiological stability and their physico-chemical equilibrium. Acidification is essential to avoid damageable consequences on the colour and the sensory quality of the wines. Of the possible modes of acidification, chemical acidification is still the most common one used by OIV country members. It consists of adding lactic, malic, tartaric or citric acids to the musts and wines. Fumaric acid, with its high acidifying power and availability on the market, could be an interesting alternative at lower cost than other acids. Very few studies describing the effects of the addition of this acid on the chemical and organoleptic quality of musts and wines have been published. The present study therefore investigated the impacts of fumaric acid – namely its solubility, acidifying power, and impacts on colour and phenolic compounds – on musts and wines in comparison to other acids. Sensory analyses were also carried out to evaluate the perception threshold of each acid in the wines and compare how the acids are perceived. Except for its low solubility, fumaric acid seems to be a good candidate for an economic alternative to wine acidification. It had the highest acidifying power and slightly affected wine chemistry and organoleptic qualities. Further studies are needed to determine the appropriate step during which this acid should be added during winemaking.
The figure below (Figure 2 in the original article) demonstrates the acid concentration needed (g/L) to decrease pH by 0.1 to 0.5 units in white and red musts and wines.
The amounts of fumaric acid and tartaric acid necessary for the same pH decrease were systematically lower than for other acids. These acids therefore had more acidifying power in musts and wines than the others. In contrast, according to the plot profiles of Figure 2, lactic acid was found to be the weakest acid, as it required the highest amount to be added to the musts and wines to lower the pH to the same target level as the other acids. Thus, the strengths of the studied acids was classified as follows: FA>TA>CA≈MA>LA in musts and FA>TA>MA>CA>LA in red wines and FA>TA>MA>CA≈LA in SB-wine.
Furthermore, in order to lower the pH of musts and wines by 0.1 units, significantly less fumaric acid (30%) was needed than tartaric acid. Thus, in addition to the fact that fumaric acid is the cheapest and most readily available acid on the market, it also has the highest acidifying power. Indeed, the results obtained here clearly show that fumaric acid is the most effective in reducing the pH of musts and wines, regardless of the type of wine. Such low quantities of added fumaric acid for decreasing pH represent a considerable financial gain for a wine cellar. The only negative point is its low solubility, but it is however higher than the doses needed to acidify must or wines. A negative aspect of tartaric acid is its possible precipitation during storage, unlike fumaric acid with which this does not occur.
Besides its high acidifying potential, fumaric acid is also known to have antimicrobial activity; it can inhibit bacterial development. These properties could allow the use of SO2 to be reduced at the vatting when FA is added to the must, protecting the must from bacterial growth or blocking a non-desired malolactic fermentation. They are of particular interest in white wines, especially in Cognac, which must be sulfite free with a high acidity. However, it should be taken into account that when added before alcoholic fermentation or in the presence of residual living yeasts, fumaric acid is converted into malic acid by yeasts via the citric acid cycle.
REFERENCE
Gancel, A.-L. ., Payan, C., Koltunova, T., Jourdes, M. ., Christmann, M., & Teissedre, P.-L. (2022). Solubility, acidifying power and sensory properties of fumaric acid in water, hydro-alcoholic solutions, musts and wines compared to tartaric, malic, lactic and citric acids. OENO One, 56(3), 137–154. https://doi.org/10.20870/oeno-one.2022.56.3.5455
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