Free beer might sound like heaven to some tailgaters on this football weekend, but consider the case of a man whose tummy was fermenting its own brew.

Suspected for five years of being a “closet drinker,” the 61-year-old man showed up in 2009 at a Texas emergency room with a blood alcohol concentration of 0.37 percent—despite not having a drop of alcohol.

“He would get drunk out of the blue,” nursing dean Barabara Cordell of Panola College in Carthage, Texas, told NPR’s “the salt” food blog. The man’s wife, a nurse, purchased a breathalyzer and found that (often after exercise or not eating) his blood-alcohol level was regularly four to five times the U.S. legal limit of 0.08 percent. (Explore a human-body interactive.)

In April of 2010, Cordell and her colleague Justin McCarthy report in a recent International Journal of Clinical Medicine, the man checked in for 24-hour observation at a hospital, where his bags were searched for booze and he was fed high-carbohydrate snacks during the day. In the afternoon of the stay, his blood alcohol level rose to 0.12 percent.

The culprit was gut fermentation syndrome, also known as auto-brewery syndrome. The man had been a home-brewer of beer and likely was regularly exposed to the brewer’s yeast, Saccharomyces cerevisiae, the fungus used to ferment beer. He probably acquired his own private brewery in 2004 after antibiotics treatment killed off his original intestinal flora and replaced it with brewer’s yeast. (Watch a video on the science of brewing.)

Thereafter, after eating carbohydrate-rich foods such as bread or bagels, the gut bugs would ferment away, merrily making an alcohol-rich brew in the man’s innards in the next 24 hours.

The story has a happy ending; the man took daily anti-fungal medications for six weeks to kill off the brewer’s yeast. During his recovery, he also had to follow “a very strict no sugar, no carbohydrate diet and did not ingest alcohol in any form,” says the study.

After years of involuntary inebriation, the last part of the treatment may have come as a relief.

Follow Dan Vergano on Twitter.