Metatartaric Acid is an organic acid derived from tartaric acid, a natural compound found in many fruits, especially grapes. It is primarily used in the wine and food industry for its ability to prevent the formation of tartrate crystals in wines and fruit juices. Metatartaric acid is produced by heating tartaric acid, a process that alters its molecular structure, giving it unique stabilizing properties.

Chemical Composition and Structure

Metatartaric acid is a polymeric form of tartaric acid, obtained through heating. This transformation modifies the molecular structure of tartaric acid, converting it into a more complex form that is less soluble and more chemically stable. This allows it to prevent crystal formation in acidic solutions such as wine.

Production Process

It is produced by heating natural tartaric acid, typically extracted from grapes. During the heating process, tartaric acid undergoes polymerization, transforming into metatartaric acid. This process must be carefully controlled to ensure the quality and purity of the final product, which can vary depending on the temperature and duration of the treatment. 

• Extraction of Tartar: Metatartaric acid is primarily produced from tartar, which is a byproduct of winemaking. Tartar is extracted from the residues of wine, particularly from the fermentation lees.

• Purification: The extracted tartar is purified to remove impurities and other undesirable substances. This may include filtration and washing processes to obtain a high-quality raw material.

• Heating: The purified tartar is heated to high temperatures to facilitate thermal decomposition and the formation of metatartaric acid. This process involves the removal of water and the restructuring of the tartaric acid molecule present in tartar.

• Crystallization: Once metatartaric acid is formed, the solution is cooled to allow the product to crystallize. The crystals are then collected and further purified if necessary.

• Quality Control and Packaging: Finally, metatartaric acid undergoes quality control checks to verify its purity and functional properties. After analysis, it is packaged for distribution and use in food and cosmetic products.

Physical Properties

It appears as a yellowish powder, slightly soluble in water, and easily incorporated into liquid solutions. It has an acidic pH, and when dissolved, it helps stabilize beverages by preventing tartrate precipitation, a phenomenon that can affect the clarity and quality of wine. 

Applications

• Wine Industry: Used as a stabilizer in wines to prevent the formation of tartrate crystals during storage and cooling. This helps improve the clarity and appearance of wine, ensuring that consumers do not find crystals in the final product.

• Food Industry: Applied in fruit juices and other beverages to stabilize solutions and prevent crystal precipitation, enhancing the quality of the product.

Ingredient on the European food additives list as E353, acidity regulator, stabilising agent in wines.

Stabilisation of tartrates in wines with cold bottling recommended, as high temperature bottling would reduce their effectiveness (1).

• Preservation: Can be used to improve the stability of acidic solutions over time, preventing degradation or crystallization. 

Other uses

Effective complexing agent for the removal of copper ions.

Safety

EFSA's Panel on Food Additives concluded that metatartaric acid (E353), assuming that metatartaric acid is fully hydrolysed pre-systematically to l(+)-tartaric acid, should be included in the group Acceptable Daily Intake (ADI) of 240 mg/kg body weight (bw) per day (2).

Health and Safety Considerations

Safety in Use
Metatartaric acid is considered safe for use in food and beverages, including wine. It is approved as a food additive in many regions worldwide, including the European Union and the United States. However, since it may degrade over time at high temperatures, it is best suited for beverages stored at moderate temperatures.

Allergic Reactions
Allergic reactions to metatartaric acid are extremely rare, as it is a natural derivative of tartaric acid, which is commonly present in foods like fruit. Nonetheless, it is always advisable to follow guidelines for food additive usage.

Toxicity and Carcinogenicity
It has been thoroughly tested and approved for food use without known risks to human health.

Environmental Considerations
Derived from a natural source like grapes, metatartaric acid is biodegradable and poses no significant environmental risks. However, its production requires energy for heating, which can contribute to the environmental footprint if not managed sustainably.

Regulatory Status
Metatartaric acid is approved as a food additive by the European Union (classified as E353) and the Food and Drug Administration (FDA) in the United States. It is widely used in the wine and food industry.

• Molecular Formula  C₈H₈O₁₀
• Molecular Weight   264.14
• CAS  39469-81-3
• UNII    
• EC Number   609-694-5
• DSSTox ID  DTXSID901205002
• IUPAC  2-[5-[carboxy(hydroxy)methyl]-3,6-dioxo-1,4-dioxan-2-yl]-2-hydroxyacetic acid
• InChl=1S/C8H8O10/c9-1(5(11)12)3-7(15)18-4(8(16)17-3)2(10)6(13)14/h1-4,9-10H,(H,11,12)(H,13,14)
• InChl Key      KWBYTEOPKORPPY-UHFFFAOYSA-N
• SMILES  C1(C(=O)OC(C(=O)O1)C(C(=O)O)O)C(C(=O)O)O

Synonyms:

• 2,2'-(3,6-Dioxo-1,4-dioxane-2,5-diyl)bis(2-hydroxyacetic acid)

References_____________________________________________________________________

(1) Sturza, R., Covaci, E., & Prida, I. (2014). Effect of different chemical additives on the tartaric stabilization of young wines. In Modern Technologies in the Food Industry (pp. 297-302).

(2) EFSA Panel on Food Additives and Flavourings (FAF), Younes, M., Aquilina, G., Castle, L., Engel, K.H., Fowler, P., Frutos Fernandez, M.J., Fürst, P., Gürtler, R., Gundert‐Remy, U. and Husøy, T., 2020. Re‐evaluation of metatartaric acid (E353) as a food additive. EFSA Journal, 18(3), p.e06031.