Why Beans Make You Fart
The 16th-century theologian Martin Luther boasted that he could drive away the evil spirit with a single fart. Just imagine what he could have done after a whole plate of beans. But where does this bean-power come from?
Farts have been called belches lost to posterity, but belches or burps are sometimes caused by swallowed air, while farts are bubbles of gas produced by bacteria in the large intestine, or colon. Kids classify them—noisy smelly, silent deadly, and so on. There is a real medical term for farts, however: "flatus" (rhymes with "hate us"), and flatulent describes both a person who farts a lot and food such as beans that tends to produce farts.
Everyone farts. Most people fart gently every now and then, producing between 10 and 40 ml of gas per hour, but some people fart much more than this, and farts are enormously increased by particular foods, including onions, cabbage, and especially beans.
Much of the food we can digest is made of proteins and carbohydrates, especially complex sugars, or polysaccharides. The polysaccharides are broken down by enzymes in the gut into oligosaccharides and then into simple sugar molecules, which are absorbed into the bloodstream and provide energy for the muscles.
However, beans contain three rogue oligosaccharides—raffinose, stachyose and verbascose—which humans cannot digest, because we lack the necessary enzyme, a-D-galactopyranosidase. These three rogues therefore go right through into the colon, where they are chewed up by bacteria, producing the gases hydrogen, nitrogen and carbon dioxide. Some people—about one in four—also produce methane, but most of us don't.
The smell of farts is partly due to traces of indole and scatole, but mainly the result of various sulphur compounds produced as by-products alongside the hydrogen and carbon dioxide. When you hold a fart in, the gases are absorbed into the bloodstream, and the hydrogen can be detected in your breath, but luckily the smell does not get through.
At a New York farting conference, a doctor described how volunteers had sat for hours with perforated rubber tubing inserted into their rectums to collect the farts, which were then analysed for quantity and composition. On a base diet they produced an average of 15 ml of gases per hour, mainly nitrogen and hydrogen, but a few hours after a meal of pork and beans the rate went up by a factor of 12 to an average of 176 ml an hour, and the farts contained masses of carbon dioxide as well.
There is great variation between people; some produce up to 500 ml per hour after eating beans.
The doctor also found that farting was greatly increased by stress. The volunteers farted much more when they sat with their rubber tubes in a passage in an open lab than when they were in a comfortable room with armchairs and a TV set.
Some people fart a lot after consuming dairy products; one flatulent man went to his doctor and eventually discovered he could not digest lactose, the main sugar in milk. When he eliminated dairy foods from his diet his farting returned to normal. For other people, sweet biscuits produce an immediate effect. If your farting bothers you, try varying what you eat and see what happens.
You can prevent farting when you eat beans by consuming with them some of that missing enzyme, which is marketed in the UK as Ido-air, and in the US as Beano. Eat a Beano tablet first, or sprinkle a drop or two on your food, and (so they claim) the farts will not come. "Now you can have peas and quiet" says their advertisement—and for a promotion they once produced a lightweight nylon jacket—a Beano windbreaker.
In her excellent Bean Book, cookery writer Rose Elliott suggests par-boiling the beans, thoroughly rinsing with cold water, and then simmering until done, but it's hard to see how this will remove those rogue oligosaccharides.
Collect Your Own
If you really want to find out how much you fart after a meal of beans, take a bath a few hours later, and take into the bath a small empty plastic bottle. Fill the bottle with water, hold it upside down, keeping the open end under the surface so that it stays full of water, and pull it up between your legs so that when you fart, the gases bubble up into the bottle. Can you beat 250 ml?
If you don’t want to stop eating beans, but find all this flatulence rather embarrassing, then just remember that you’re not alone—everyone does it. Edward de Vere, Earl of Oxford farted loudly as he bowed to Queen Elizabeth I, and was so ashamed that he travelled abroad for seven years. When he returned to her majesty's presence, however, the first thing she said was "My Lord, I had forgot the fart."