Acetic and propionic acids

Vinegar has been known as the natural result of air exposure of beer and wine, as acetic acid-producing bacteria are present in nature. Today, the biological route accounts for only approximately 10% of worldwide acetic acid production, but it remains important for vinegar production. Similarly, the bioproduction of propionic acid is not economically competitive with petrochemical routes, although, since early last century, a number of pilot plants have been designed and built to produce propionic acid by fermentation processes. The goal of this article is to focus on several aspects of acetic acid and propionic acid production: the acid-producing bacterial strains and the metabolic pathways of acid biosynthesis, as well as the aerobic and anaerobic fermentation processes. At the end, the downstream processes to separate the products efficiently are discussed.