Burping (also known as belching, ructus, or eructation) is the release of gas from the digestive tract (mainly esophagus and stomach) through the mouth. It is usually accompanied with a typical sound and, at times, an odor.
Burping is generally caused by swallowing air when eating or drinking and subsequently expelling (or inhaling) it, so in this case the expelled gas is mainly a mixture of nitrogen and oxygen. Burps can also be caused by consuming carbonated drinks such as beer, soft drinks, energy drinks or champagne, in which case the expelled gas is primarily carbon dioxide from the drink itself. Common diabetes drugs metformin and Byetta can cause burping, especially at higher doses. This often resolves in a few weeks. Burping combined with other symptoms such as dyspepsia, nausea and heartburn may be a sign of an ulcer or hiatal hernia, and should be reviewed by a physician. Other causes of burping include: food allergy, gallbladder problems, acid reflux disease, H. pylori, and gastritis.
The source of the sound of burping is unknown, but might be due the rapid passage of air through the lower esophageal sphincter [Lang et al Am. J. Physiol 307:G452-G458, 2014] . The current Guinness world record for the loudest burp is 109.9 dB, set by Paul Hunn on 23 August 2009. (This is louder than a jackhammer at a distance of 1 meter.)
In microgravity environments, burping is normally associated with regurgitation. The valve at the top of the stomach (the gastroesophageal junction) does not produce a tight seal, and in the absence of gravity, the stomach contents tend to float near this loose seal, making them likely to come up along with the expelled air.
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Babies are particularly subject to accumulation of gas in the stomach while feeding, and this can cause considerable discomfort and agitation unless the child is burped. The act of burping an infant involves placing the child in a position conducive to gas expulsion (for example holding the infant up to the adult's shoulder, with the infant's stomach resting on the adult's chest) and then lightly patting the lower back so that the child burps. Because burping can cause vomiting in infants, a "burp cloth" or "burp pad" is sometimes employed on the shoulder to protect the adult's clothing.
Some cultures, notably Chinese and Indian, regard burping as acceptable in certain situations. In Japan, burping during a meal is considered bad manners. In others, particularly Western cultures, such as North American, French, German, Italian and British cultures, burping is also deemed socially inappropriate. In Middle Eastern countries it is not acceptable to burp out loud, and one should silence one's burp, or at least pretend to do so.
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.
In other animals
Many other mammals, such as cattle, dogs and sheep, also burp. In the case of ruminants, the gas (wind) expelled is methane produced as a byproduct of the animal's digestive process. This methane is produced exclusively by a narrow cohort of methanogenic archaea; Escherichia coli (E. coli) and other bacteria lack the enzymes and cofactors required for methane production. Cows are thought to emit an average of 542 litres (if located in a barn) and 600 litres (if in a field) of methane per day through burping and exhalation, making commercially farmed cattle a major[quantify] contributor to the greenhouse effect. 95% of this gas (wind) 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 cattle burps.
One reason why cattle 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.
In some animals, a failure to burp successfully can be fatal. This is particularly common among domesticated ruminants that are allowed to gorge themselves on very rich[clarification needed] spring clover or alfalfa. The condition, known as bloat, is a high pressure buildup of gas in the stomach(s) 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.
Some fish are also known to expel air from their gills; here the burp is produced by gas being expelled from the gas bladder.
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