Many people have noticed that beans can have an effect on the gastrointestinal tract, which often manifests in the form of gas. This tendency is so linked with beans that a popular children's rhyme references it. Many other foods can also increase gas, however, including other legumes, cauliflower, cabbage, Brussels sprouts, and onions. This is because certain sugars in these foods are difficult for the human body to break down; beans cause gas because they are often particularly high in this sugar.
Although most people may not be aware of this, the bulk of the gas created by beans is actually odorless. The scented part is primarily volatile sulfur compounds. Specific gases like sulfur may also be released as bacteria in the gut process other parts of a meal. Although the gas may not smell very good, it is not generally harmful. Diners may want to avoid combining beans with other odorous foods like members of the onion family if they are particularly concerned.
The substance in beans that causes gas is oligosaccharide, a type of sugar that 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 that tends to increase gas. In addition, they are often combined with dairy products in burritos and other Mexican foods; many people are familiar with the aftereffects of such food, especially when it is eaten quickly. It appears that eating fast makes it more difficult for the body to break down food, increasing the chance of gas. Stress can also contribute to the issue.
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 them, and rinsing them as well. Canned beans should be thoroughly rinsed as well. Water appears to rinse away some of the gas-causing sugar, 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.