Tartaric acid is a dihydroxyl derivative of succinic acid. As there are two asymmetric carbon atoms in its molecule, so it exists in four different stereoisomers: L, D, DL and Meso. The L and DL forms are commonly used as food additives.

1. L-Tartaric Acid
When it comes to tartaric acid, we’re mostly talking about L-(+)-tartaric acid, the dextro form which with the CAS number 87-69-4 and E number E334. It is used widely like other acidulants (citric acid and malic acid) for its high solubility, strong tart taste (about 1.2 to 1.3 times that of citric acid), and its stable salts.

Natural Source

L tartaric acid is widely present in nature and mostly in the form of potassium, calcium and magnesium salts or free state. It can be found in a variety of plant fruits such tamarinds, grapes, bananas. Tartaric acid is another major grape acid, along with malic acid. But unlike malic acid, its concentration does not decline much during the grape ripening process.

How is it Made?
Generally, there are three production methods to obtain this ingredient: by-products of winemaking/grape, enzyme process, and microbial fermentation. The first method is commonly used among European manufacturers for the abundant raw materials – grapes, while China is the biggest manufacturers for the second method.

1. Winemaking byproduct

During the winemaking process, a part of tartaric acid is precipitated in the form of cream of tartar crystals (potassium bitartrate), or more lovingly, “wine diamonds”. The first step of production is the recrystallization of cream of tartar as its solubility increases along with the rising temperature.

Then reacting it with calcium hydroxide and calcium chloride to produce calcium tartrate (insoluble).


And finally, L tartaric acid is obtained by reacting calcium tartrate with sulfuric acid. It can also be extracted from the grape.

For your better understanding, the following are the four steps reaction equations:

Cream of tartar (Recrystallization) → KHC4H4O6
2KHC4H4O6 + Ca(OH)2 → CaC4H4O6 + K2C4H4O6 + 2H2O
K2C4H4O6 + CaCl2 → CaC4H4O6 + 2KCl
CaC4H4O6 + H2SO4 → CaSO4 + C4H6O6
It is shown in the European Parliament that the total output quantity in 2016 was around 35, 000MT, and 86% was produced in Europe. (1)

2. Enzyme process

The enzyme method is the mainstream commercial production method of L tartaric acid in China due to the high purity, high conversion efficiency, and safety. The manufacturing flow chart as follows:


l tartaric acid enzyme production

Maleic anhydride is oxidized to sodium cis-epoxysuccinate by hydrogen peroxide.
Sodium cis-epoxysuccinate is hydrolyzed to tartaric acid using cis-epoxysuccinate hydrolase (ESH)
3. Fermentation method

Using glucose as raw material, through microbial fermentation, the glucose is oxidized to 5-keto-D-gluconate (5-KGA), and then catalyzed to L- tartaric acid.

l tartaric acid glucose fermentation

2. D-Tartaric Acid
It is not the natural form and seldom used in food, also known as D(-)-tartaric acid with the CAS number 147-71-7, it can be obtained by chiral split DL tartaric acid.

3. DL-Tartaric Acid

Racemic tartaric acid is a mixture of equal amounts of L and D, the CAS number 133-37-9. Its manufacturing flow chart is similar to that of producing L tartaric acid by enzyme but without the enzyme used in the hydrolysis process. DL tartaric acid can be used as a PH regulator, chelating agent, and also used to produce tartrates.

4. Meso Tartaric Acid
CAS number 205-696-1. It is optically inactive due to internal molecular symmetry.