Belching

 Belching, also known as burping, ructus, or eructation, involves 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.

Physiology
Belching is typically caused by swallowing air (aerophagia) when eating or drinking and subsequently expelling it, so in this case the expelled gas is mainly a mixture of nitrogen and oxygen. Burps can also be caused by drinking carbonated drinks such as beer, soft drinks, or champagne, in which case the expelled gas is carbon dioxide from the drink itself. Common diabetes drugs metformin and Byetta can cause belching, especially at higher doses. This often resolves in a few weeks. Belching 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.

The sound of burping is caused by the vibration of the upper esophageal sphincter as the gas passes through it. The current Guinness world record for the loudest burp is 107.1 dB, set by Paul Hunn in 2008. (This would be noticeably louder than a chainsaw at a distance of 1 metre.)

Terminology
In the United States, "burping" is significantly quieter and subtler than "belching".

Social context and etiquette
In many parts of the world, especially in formal situations, audible burping is considered impolite. Public belching tends to be received in a manner similar to flatulence.

Infant burping
Babies are particularly subject to accumulation of gas in the stomach while feeding, and this can cause considerable agitation and/or discomfort 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 holding the infant up to the adult's shoulder, with the infant's stomach resting on the adult's chest) and then lightly patting it on the lower back so that he or she burps. This practice is not universal, for instance in the Czech Republic, there is no tradition of burping babies.

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

In animals
Many other mammals, such as cattle, dogs, and sheep also burp. In the case of ruminants, 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 exhalation, making commercially farmed cattle a major contributor to the greenhouse effect. 95% of this gas is emitted through belching. 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 that domesticated cows burp so much is because they are often fed foods that their digestive systems did not evolve to 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 spring clover or alfalfa. The condition, known as bloat is basically a high pressure build up of gastric gasses and requires immediate veterinary treatment, usually the insertion of a flexible rubber hose down the esophagus or in extreme cases the lancing of the animal's side with a scalpel to expel the build up of gas.

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