Eight inmates have fallen ill at a prison in Utah, after drinking a homemade “jailhouse wine.” The wine was created by a particular inmate who mixed juice, fresh and canned fruit, as well as water in a bag.

The mix became infected with the bacterium Clostridium botulinum, which causes botulism, after a contaminated potato was added to the concoction as an “experiment.” The wine-making inmate had hidden the bag of wine under his mattress for a week to allow it to ferment.

In a study that reviewed the botulism cases at the prison, doctors analyzed what may have caused the outbreak from the “pruno,” which is what the inmates coined the homemade wine. “Potato in the pruno recipe was associated with botulism,” the report concluded.

Botulism is rare but serious. There are several different types of infection, including foodborne botulism, transmission through a wound, or the ingestion of the spores of bacteria, that ultimately begin to grow in the intestines, releasing the nerve toxin that paralyzes muscles. According to the Centers for Disease Control and Prevention (CDC), there are only about 145 cases of botulism that occur per year. Fifteen percent are foodborne.

After having a taste of the pruno, eight inmates began experiencing the signature symptoms of botulism: slurred words, difficulty breathing, and double vision. Botulism affects the muscles, starting from the top of the head and slowly moving down until ultimately it paralyzes the muscles that control breathing. “It can take weeks to months [to recover],” Dr. Megan Fix, a lead author of the study and assistant professor of surgery at the Division of Emergency Medicine at the University of Utah Hospital, told ABC News. “You have to just wait it out. The nerve endings will have to wake up … Essentially your nerve endings have to make a new receptor.”

The botulism bacterium releases a nerve toxin that links to nerve receptors and disrupts their reactions. “The brain is functioning perfectly fine, but you can’t control your muscles,” Fix told ABC News. “That’s why [the inmate] was so scared. His brain was working, but he couldn’t control what was going on. He knew he was getting weaker and weaker.”

The inmate who created the pruno told doctors that he had made this type of alcohol “20 times before,” but this time he had added a potato to the mix to experiment. “He didn’t have a great explanation for why he experimented,” Fix told ABC News.