Caftaric acid

Caftaric acid is a non-flavonoid phenolic compound.

It is found in the juice of grapes (Vitis vinifera) and impacts the color of white wine.

It is an esterified phenolic acid, composed of caffeic acid, a hydroxycinnamate produced by plants, and tartaric acid, the principal organic acid found in grape berries. As such, caftaric acid is found in all grape juices and wines. During alcoholic and malolactic fermentation, the ester can be enzymatically hydrolysed, releasing the two constituents. Caffeic acid is susceptible to chemical oxidation, and subsequent redox reactions involving caffeic acid can contribute to wine browning over time, and the straw-gold color that can develop in some white wines after bottling.

Aside from wine, it is abundantly present in raisins. It also occurs in Cichorium intybus (common chicory) and is one of the bioactive components of Echinacea purpurea (Eastern purple coneflower).

Caftaric acid has a good bioavailability when fed in rats. Intact trans-caftaric acid was detected in rat plasma along with its O-methylated derivative trans-fertaric acid.

In wine
Winemakers measure caftaric acid levels as their primary method to estimate the oxidation levels that a wine has undergone. For example, press wines, which undergo a high degree of oxidation, will have little to no caftaric acid.

Grape reaction product (2-S glutathionyl caftaric acid) is an oxidation compound produced from caftaric acid and found in wine. Malvidin 3-glucoside alone is not oxidized in the presence of grape polyphenol oxidase (PPO), whereas it is degraded in the presence of a crude grape PPO extract and of caftaric acid, forming anthocyanidin-caftaric acid adducts.