Autobrewery is a process by which the body produces alcohol endogenously and without drinking.

Alcohol is produced inside the body from sugars and other carbohydrates by a process called fermentation. Scientific consensus suggests that autobrewery would not produce significant alcohol levels in healthy individuals, though disease states, diet, and/or medications may enhance alcohol production by autobrewery. Metabolic disorders which impair the body’s ability to eliminate alcohol will increase alcohol concentrations in the body. Therefore, the alcohol produced naturally by the body would build up to high levels, and this would naturally add to alcohol which was actually drunk by the individual. Such metabolic disorders are most commonly found in people of Japanese descent. Secondly, yeast infections in the gastrointestinal tract produces autobrewery which can result in very high BACs. In fact, one case report details a case where a female had BACs in excess of 3 times the legal limit. Continuous monitoring in a rehabilitation facility excluded alcohol drinking as an explanation and her aspirate grew abundant amounts of yeast. Endogenous alcohol production is highest when ingesting food high in carbohydrate content, since this is a starting material for fermentation. Finally, in one case I consulted on, a supplement for cholesterol called Red Yeast Rice caused intoxication above the legal limit, because, as the name suggests, this product contained yeast.

Intoxication as a result of autobrewery would constitute involuntary intoxication. To assess whether autobrewery is a valid defense, I would look for evidence of yeast infections, alcohol metabolism disorders, or ingestion of the supplement Red Yeast Rice.