Many people have noticed that beans have a deleterious gastrointestinal effect, which often manifests in the form of gas. This tendency is so linked with beans that a popular children's rhyme references it, although beans bear an unfair portion of the reputation. Numerous other foods can also increase gas, such as other legumes, cauliflower, cabbage, Brussels sprouts, and onions. This is because of certain sugars in these foods which are difficult for your body to break down; beans cause gas often because they are particularly high in this sugar.

You may not be aware of this, but when beans cause gas, the bulk of the gas is actually odorless. The scented part of the gas is primarily methane, a gas which is not produced by all people. Specific gases like sulfur may also be released as bacteria in your gut process other parts of your meal. When beans cause gas, although it may not smell very good, it is not generally harmful. You may want to avoid combining beans with other odorous foods like members of the onion family if you are particularly concerned.

The substance in beans which causes gas is oligosaccharide, a type of sugar which is not normally digestible by the human body. Beans cause gas when this sugar enters the large intestine, which hosts an abundance of bacteria. Since the sugar has not been broken down at earlier stages of the digestive process, these bacteria seize upon it as a source of nutrition, consuming it and quickly multiplying. The resulting gas is a byproduct of the digestive process of the bacteria.

Beans are also high in fiber, another substance which tends to increase gas. In addition, they are often combined with dairy products in burritos and other Mexican food; many people are familiar with the aftereffects of Mexican food, especially when it is hastily consumed. It appears that hasty consumption inhibits the abilities of your body to break down food, increasing the chance of gas. Stress can also contribute to the formation of gas.

Undercooked beans cause gas in larger amounts. People who want to reduce the risk may want to consider soaking their beans for at least eight hours before cooking, and rinsing them as well. Canned beans should be thoroughly rinsed as well. This appears to rinse away some of the gas-causing sugar, thus making the beans less potentially volatile. It also happens to shorten the cooking time, which can be convenient for cooks in a hurry. When cooking beans, it is important to make sure that they cook all the way to softness.

Incidentally, if you're curious about the etymology of the word “fart,” commonly used to describe the results of bean consumption, it is an Old English word of imitative origin.