Bacterial production of diacetyl and actoin in wine

Wines which have undergone malo‐lactic fermentation contain significantly more diacetyl and acetoin than wines which have not. The amounts of diacetyl and acetoin formed depend on the type of bacterium present and on the composition of the wine. Leuconostoc mesenteroides is the chief organism forming these products in Australian wines while pyruvic acid and citric acid are the chief substrates from which they are formed. The presence of a few g. per litre of glucose interferes with the formation of these products in wine. The heterofermentative rods, Lact. hilgardii and Lact. brevis, which are responsible for malo‐lactic fermentation in some Australian wines, produce diacetyl and acetoin only under conditions unlikely to occur in wines. Homofermentative lactobacilli have not yet been isolated from Australian wines.