It all began when the man checked himself into a Texas emergency room complaining of dizziness, reports NPR.
A breath test soon revealed he was almost five times over the legal limit, yet the man claimed he hadn't taken a sip of (alcohol) that day.
Doctors were stumped, but put it down to the man being a closet alcoholic.
But one team of medical professionals were determined to solve the mystery.
"He would get drunk out of the blue - on a Sunday morning after being at church, or really, just anytime," says Barabara Cordell, the dean of nursing at Panola College in Carthage, Texas. "His wife was so dismayed about it that she even bought a Breathalyzer."
Isolated in a hospital room for 24 hours, Cordell and gastroenterologist Dr. Justin McCarthy fed the man carbohydrate-rich foods, with regular blood-alcohol checks along the way.
After the series of tests conducted by the pair, the man's intestinal tract was found to be acting like his own brewery.