Dr. Carien Coetzee
26 April 2023
The decreased concentration of organic acids in grape berries due to global warming often necessitates the acidification of musts and/or wines in order to preserve the microbiological stability and their physico-chemical equilibrium. Fumaric acid seems to be a good candidate for an economic alternative to wine acidification. In this blog post, the use of fumaric acid in winemaking is explored.
Fumaric acid in nature
Fumaric acid was isolated for the first time from the plant Fumaria officinalis. It is naturally produced in various biological systems since it is an intermediary metabolite in the citric acid cycle, also known as the Krebs cycle. The cycle is used by all living organisms that respire, as opposed to those that ferment.
Is fumaric acid naturally present in grapes?
In grape berries, small amounts of fumaric acid (0.07-10.69 mg/L) have been found1–3.
Fumaric acid in the food industry
Known for being the least expensive of the food-grade acids and being nontoxic, fumaric acid is mostly used in the food industry as an antibacterial agent and acidulant4. Examples of use include certain dairy-based products, certain beverages, breakfast cereals and processed meats and spreads, and salt and vinegar potato chips.
Fumaric acid effect on pH (acidifying power)
Wine acids differ significantly in their acidification power meaning that some acids are stronger than others. A recent study5 investigated the acidification power of the main wine acids by reporting the acid concentration needed to decrease the pH by 0.1 units in real musts and wines. Results showed that the amount of fumaric acid and tartaric acid needed to decrease the pH was systematically lower when compared to the other acids included in the study (citric acid, malic acid and lactic acid). These two acids, therefore, had higher acidifying power in musts and wines. It is interesting to note that significantly less (30%) fumaric acid was needed to lower the pH when compared to tartaric acid.
The strengths of the studied acids were classified as follows (tested in real musts and wines):
For musts: Fumaric acid > Tartaric acid > Citric acid ≈ Malic acid > Lactic acid
For Sauvignon blanc wine: Fumaric acid > Tartaric acid > Malic acid > Citric acid ≈ Lactic acid
For red wines: Fumaric acid > Tartaric acid > Malic acid > Citric acid > Lactic acid
Therefore, fumaric acid can be considered as a strong acidulant. This means that a smaller amount of fumaric acid is required to acidify the product in comparison with other organic acids. These low quantities of added fumaric acid to decrease pH represent a considerable financial gain for a producer.
Antibacterial properties of fumaric acid
Many publications describe the antibacterial properties of fumaric acid. The strong acidifying properties of fumaric acid (lowering of pH) help to limit bacterial development and growth6. The antibacterial properties of fumaric acid have also been investigated in wines.
- A study showed that the addition of fumaric acid at concentrations higher than 360 mg/L retarded malolactic fermentation7.
- Another study8 showed that, at concentrations of between 300 and 600 mg/L, fumaric acid was able to inhibit malolactic fermentation (Oenococcus oeni) even with large bacteria populations present while 150 mg/L was able to delay the beginning of malolactic fermentation for several days8
- Dosages of ≥50 mg/L of sulphur dioxide and ≥300 mg/L fumaric acid added to wine had the same effects on bacterial populations and malic acid concentrations9. The inhibitory effect of fumaric acid is, however, more stable over time, since free SO2 is transformed into bound forms, reducing its inhibitory effect.
The ability of fumaric acid to inhibit/delay the growth of lactic acid bacteria is of interest for high pH wines, such as wines from warm regions10–12. Additionally, the antimicrobial properties of fumaric acid mean that the addition to the must could decrease the need for sulphur dioxide by protecting the must from bacterial growth. Therefore, fumaric acid is of particular interest for the production of low-sulphur and/or high pH white wines. It is important to note, however, fumaric acid is only inhibitory to lactic acid bacteria and not acetic acid bacteria.
How does fumaric acid affect yeasts?
Fumaric acid does not affect yeast metabolism and is therefore a tool to inhibit malolactic fermentation without affecting alcoholic fermentation13. It can be especially useful to apply during bottle fermentation of natural sparkling wines. However, the effect of fumaric acid added before alcoholic fermentation (or in the presence of residual living yeasts) should be considered as yeast can convert fumaric acid into malic acid via the citric acid cycle14–16.
Solubility of fumaric acid
A study5 compared the solubility of the main acids used in winemaking (tartaric, malic, citric and fumaric acid). Results showed that citric acid was the most soluble followed by malic and tartaric acid, which in many cases were very similar in their solubility. Fumaric acid showed the lowest solubility. This property constitutes the main obstacle to its use in winemaking. However, the solubility tests showed that the authorised quantity of 3 g/L for acidification in wine in the USA is less than the solubility value17. The oenological use of this acid should therefore not pose significant solubility problems.
Fumaric acid can have an effect on the sensory properties of the product it is added to18. It is known to have a fruity-like taste19 and a persistent, long-lasting sourness due to its hydrophobic nature4.
- The sensory evaluation of wine acids in water20 showed that fumaric acid and tartaric acid are perceived as more astringent compared to other food acidulants and that fumaric acid is sourer than malic acid and citric acid. In wines, the comparison of three wine acids showed that the relative sourness ranked fumaric acid > malic acid > citric acid on a pound-weight basis, in an order of lowest to highest molecular weight21.
- In another study, the addition of fumaric acid to wine either had no, or very little effect, on the sensory characteristics of the wines. During the triangular tests, panellists could not tell the difference between treated wines (300 and 600 mg/L fumaric acid) and controls (0 mg/L fumaric acid). During the preference sensory test comparing wines treated with 600 mg/L fumaric acid and controls, panellists detected slight increases in acidity and body in the wines to which fumaric acid was added8.
- A different study performed a similar test and results showed that no differences were perceived between the (fumaric acid) acidified wine and the control (non-acidified wine)5. Panel members were also not able to distinguish between the wines acidified with either tartaric acid or malic acid and the wine acidified with fumaric acid.
It seems that fumaric acid is not subject to precipitation as is the case with tartaric acid. It also does not affect wine colour, turbidity and stability8.
Regulations and recommended dosage
Fumaric acid has been declared legal for use by the European Union (Commission Delegated Regulation (EU) 2022/68) as an additive to wine to delay or prevent malolactic fermentation. It was previously approved by the OIV in July 2021 (Resolution, OIV-OENO 581A-2021). The permissible use of fumaric acid for the primary application of lowering wine pH is being evaluated.
The addition of fumaric acid to wine is not yet legal in South Africa. An application to have it incorporated into South African legislation must be lodged with the Department of Agriculture by an intended supplier of the product.
The use of fumaric as an additive is permitted in the European Union at dosages of 300 – 600 mg/L. It is only allowed to be added after fermentation completion i.e., in wine. The objectives for its addition are to control the growth and activity of lactic acid bacteria responsible for malolactic fermentation in wine, to reduce sulphur dioxide dosages and to preserve malic acid. Fumaric acid addition to wine is also permitted in the USA and New Zealand22.
- Commission Delegated Regulation (EU) 2022/68 of 27 October 2021 amending Delegated Regulation (EU) 2019/934 supplementing Regulation (EU) No. 1308/2013 of the European Parliament and of the Council regarding authorised oenological practices. https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32022R0068&from=EN
- Resolution OIV-OENO 581A-2021: Treatment with fumaric acid in wine to inhibit malolactic fermentation. https://www.oiv.int/public/medias/8084/en-oiv-oeno-581a-2021.pdf
Fumaric acid is a potential alternative additive to delay, prevent or stop malolactic fermentation. It can be particularly useful in high pH, low acidity wines from warmer climates.
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