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 often audible.

Physiology

Burping is typically caused by eating or drinking too fast, and thereby swallowing (aerophagia) and subsequently expelling air, in which case the expelled gas is a mixture of nitrogen and oxygen. Burps can also be caused by imbibing carbonated drinks such as beer, soft drinks, or champagne, in which case the expelled gas is carbon dioxide from the drink itself. Gastroesophageal reflux disease can also cause involuntary burping. Some studies ( [1]) have suggested that aerophagia is not the primary culprit but that burping is in fact a learned (social) behaviour.

The sound of burping is caused by the vibration of the cardia (esophageal sphincter) as the gas passes through it. The current world record for the loudest burp is 118.1 decibels, set by Paul Hunn from London, England. (This would be noticeably louder than a chainsaw in a 1 meter diameter.) Similar sounds, such as that created by Tupperware, are sometimes also referred to as burps.

Social context and etiquette

In the Western world burping (particularly audible burping) is considered impolite (although not as socially unacceptable as farting), and so some people will cover the mouth with their hand in the same fashion as one used to guise a yawn. In India and many other countries in burping after eating is considered complemetary to the chef.

Infant burping

Babies are particularly subject to accumulation of gas in the stomach whilst feeding, and this can cause considerable agitation to the child unless it is burped. The act of burping an infant involves placing the child in a position conducive to gas expulsion (for example over the adult's shoulder, with the infant's stomach resting on the adult's chest) and then lightly patting or rubbing it on the back so that it burps.

Because burping can cause vomiting in infants, a euphemistically-named burp cloth or burp pad is sometimes employed on the shoulder to protect the adult's clothing.

"Burped" speech

It is possible to voluntarily induce burping by swallowing air and then expelling it, and by manipulation of the vocal tract produce burped speech.

While this is often employed by children 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 Animals

Other mammals, such as horses, cows, and sheep also burp; in these cases, the gas expelled is actually methane produced as a byproduct of the animal's digestive process. Anaerobic organisms such as Escherichia coli (E Coli) and methanogenic archaea produce this effect. An average cow is thought to emit between 542 litres (if located in a barn) and 600 litres (if in a field) of methane per day through burping and farting, making commercially farmed cattle a major contributor to the greenhouse effect.

Some fish are also known to expel air from their gills; here the burp is produced by gas being expelled from the gas bladder.

External links

• Burping as a behavioural problem
• Cow methane production