Turns out the smallest micro-brewery might be in your gut.
One 61-year-old man initially confounded doctors and his wife by spontaneously becoming drunk even when he hadn't ingested any alcohol.
The episodes started after the man had surgery on his foot and took a round of antibiotics. Suddenly, just two beers would make him intoxicated. Eventually, a stick of gum or liqueur in a chocolate could raise his blood-alcohol concentration past the legal limit.
For five years, the man would become intoxicated even if he had no or very little alcohol. He was admitted to the emergency room at one point with a blood-alcohol level of 0.37 percent, more than four times the legal limit.
Emergency room doctors thought the Texas man was a closet drinker. But his wife, a nurse, suspected there was an underlying medical condition and bought a Breathalyzer.
When his wife started to monitor his breath, she found that his blood-alcohol level was often 0.33 percent to 0.40 percent.
Eventually, doctors sent the man to a lab for observation and gave him a high-carb diet. Although researchers kept him from ingesting any alcohol, the man's blood-alcohol level reached 0.12 percent.
Further tests revealed high levels of saccharomyces cerevisiae, also known as brewer's yeast, were residing in his intestines.
Dr. Dan Peterson, a clinical pathologist and assistant professor in the Department of Pathology at Johns Hopkins University in Baltimore, said it's likely that when the man took a round of antibiotics, he cleared out the bacteria that normally resided in his gut. He likely ate food or had a beer with brewer's yeast at some point that was able to remain in his intestine.
"He didn't have this problem four or five years ago," Peterson said. "It really shows the dynamic effect of microbiota [human microbes] on your gut and what you eat."
While intestines are constantly fermenting food into calories, the food was being turned into alcohol in this case. Whenever the man ate carbohydrates, the yeast fermented the carbs and sugars into ethanol that was then absorbed into his blood stream.
"Really [this yeast] evolved to make beer and wine and bread. It's not evolved to live in our colon," Peterson said.
After his diagnosis, the man was put on a strict diet that cut out all carbohydrates, sugar and alcohol. In addition, he was put on anti-fungal medications for 10 weeks, after which there was no longer any sign of the brewer's yeast in his system. He stopped becoming drunk without alcohol.
While his symptoms stopped, Peterson points out that the man's syndrome could have lasting consequences, especially for his liver and heart.
"It could not have been good for him; high levels of alcohol isn't good for anybody," Peterson said.
While Peterson said the case is extremely rare, it does highlight how important gut bacteria are on overall health.
"We don't eat alone," Peterson said. "We have a microbe community that eats alongside us and takes and transforms food into things that are good for us or bad for us and in this case made the man directly sick."