2,3-Butanediol fermentation is anaerobic fermentation of glucose with 2,3-butanediol as one of the end products. The overall stoichiometry of the reaction is 2 pyruvate + NADH --> 2CO2 + 2,3-butanediol. Butanediol fermentation is typical for the facultative anaerobes Klebsiella and Enterobacter and is tested for using the Voges–Proskauer (VP) test. There are other alternative strains that can be used, talked about in details in the Alternative Bacteria Strains section below. The metabolic function of 2,3-butanediol is not known, although some have speculated that it was an evolutionary advantage for these microorganisms to produce a neutral product that's less inhibitory than other partial oxidation products and doesn't reduce the pH as much as mixed acids. There are many important industrial applications that butanediol can be used for, including antifreeze, food additives, antiseptic, and pharmaceuticals. It also is produced naturally in various places of the environment. Comparison with mixed acid fermentation 2,3-butanediol fermentation produces smaller amounts of acid than mixed acid fermentation, and butanediol, ethanol, CO2 and H2 are the end products. While equal amounts of CO2 and H2 are created during mixed acid fermentation, butanediol fermentation produces more than twice the amount of CO2 because the gases are not produced only by formate hydrogen lyase like they are in the mixed acid fermentation 2,3 Butanediol is produced at varying levels in aerated fermentations as long as the dissolved oxygen level is limiting (i.e., the culture is trying to consume more oxygen than is available). The degree of oxygen limitation dictates the ratios of 2,3-butanediol to by-products produced Butanediol properties Butanediol has various properties that help contribute to its many industrial applications and effect how it is processed during manufacturing. Butanediol is an odorless and colorless liquid. It has a high boiling point, 180-184 °C that can impact downstream processes and cause problems while recovering the fermented slurry. It also has a low freezing point, which allows it to be used for industrial applications. Industrial applications 2,3-butanediol has a variety of industrial applications and products it can produce. The levo isomer of butanediol has a low freezing point of -60 °C, which allows it to work as an antifreeze agent. Through catalytic dehydrogenation, butanediol can form diacetyl. Diacetyl is a food additive that can be used to add flavor. 0.1% butanediol will kill most pathogenic bacteria due to its antiseptic properties. Through esterification, forms of precursors of polyurethane foams are produced. These