Burping is usually caused by swallowing air when eating or drinking and subsequently expelling it, in which case the expelled gas is mainly a mixture of nitrogen and oxygen.
Burps can be caused by drinking beverages containing carbon dioxide, such as beer and soft drinks, in which case the expelled gas is mainly carbon dioxide.
Diabetes drugs such as metformin and exenatide can cause burping, especially at higher doses. This often resolves in a few weeks.
Chest pain associated with burping can occur, but is rare.
Society and culture
Acceptance
Some cultures regard burping as acceptable in certain situations, for example in South Asia it signals the host that the guest has enjoyed the food and is full. In Japan, burping during a meal is considered bad manners. Burping during a meal is also considered unacceptable in Western cultures, such as North America and Europe. In Middle Eastern countries it is not acceptable to burp out loud in public, and one should silence one's burp, or at least attempt to do so.
Infants
are likely to accumulate gas in the stomach while feeding and experience considerable discomfort until assisted. Burping an infant involves placing the child in a position conducive to gas expulsion and then lightly patting the lower back. Because burping can cause vomiting, a "burp cloth" or "burp pad" is sometimes employed on the shoulder to protect clothing.
It is possible to voluntarily induce burping through swallowing air and then expelling it, and by manipulation of the vocal tract produce burped speech. While this is often employed as a means of entertainment or competition, it can also act as an alternative means of vocalisation for people who have undergone a laryngectomy, with the burp replacing laryngeal phonation. This is known as esophageal speech.
Other animals
Many other mammals, such as cows, dogs and sheep also burp.
Ruminants
Much of the gas expelled is produced as a byproduct of the ruminant's digestive process. These gasses notably include a large volume of methane, produced exclusively by a narrow cohort of methanogenic archaeain the animal's gut; Escherichia coli and other bacteria lack the enzymes and cofactors required for methane production. A lactating cow produces about 322g of methane per day, i.e. more than 117kg per year through burping and exhalation, making commercially farmed cows a major contributor to anthropogenic methane emissions, and hence to the greenhouse effect. 95% of this gas is emitted through burping. This has led scientists at the Commonwealth Scientific and Industrial Research Organisation of Perth, Australia, to develop an anti-methanogen vaccine to minimize methane in cow burps. One reason why cows burp so much is that they are often fed foods that their digestive systems cannot fully process, such as corn and soy. Some farmers have reduced burping in their cows by feeding them alfalfa and flaxseed, which are closer to the grasses that they had eaten in the wild before they were domesticated. The failure to burp successfully can be fatal. This is particularly common among domesticated ruminants that are allowed to gorge themselves on spring clover or alfalfa. The condition, known as ruminal tympany, is a high-pressure buildup of gas in the stomach and requires immediate treatment to expel the gas, usually the insertion of a flexible rubber hose down the esophagus, or in extreme cases the lancing of the animal's side with a trochar and cannula.
Birds
There is no documented evidence that birds burp, though ornithologists believe that there is nothing which physiologically prevents them from doing so. However, since the microbiota of birds do not include the same set of gas-producing bacteria that mammals have to aid in digestion, gas rarely builds up in the gastrointestinal tracts of birds.
