Organic Acids

Organic acids are the small, non-aromatic molecules that carry one or more carboxylic-acid (–COOH) groups — the sour, tart principles of fruits and saps. Familiar members include malic acid (apples), citric acid (citrus), tartaric acid (grapes), and the volatile shorter-chain acids such as formic, valeric, and angelic acid. Their acidity comes directly from those carboxyl groups, which readily give up a proton in solution.

As a group they are close to ubiquitous, because most are intermediates of ordinary plant metabolism. The acids of the Krebs (citric-acid) cycle — citric, malic, succinic, fumaric — turn up in virtually every living tissue, while others accumulate in specific organs to set fruit sourness and buffer cellular pH. Their concentration is a large part of what gives a fruit or sap its characteristic sharpness.

The boundary that defines this class is one of structure. It gathers the simple aliphatic acids — malic, citric, tartaric, formic, valeric, angelic, gluconic, glycolic and their kin — while the ring-bearing phenolic acids and the long-chain fatty acids are classified separately. In short, if an acid is neither aromatic nor a fatty acid, it belongs here.

Medicinally the group is overwhelmingly benign and largely food-grade: malic and citric acid are everyday additives, and the class contributes to flavour, metal chelation, and gentle exfoliation or astringency. The caveats are those of concentration and irritancy rather than systemic poisoning — formic acid delivers the sting of nettles and ant bites, and oxalic acid can irritate tissues and bind minerals — so the character of an organic acid depends heavily on its dose and form.