Burping is generally caused by swallowing air 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 beverages, such as beer, soft drinks, energy drinks, and wine 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 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 m (3 ft 3 in).
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.
Inability to burp is uncommon, and chest pain caused by dysfunction of the belch reflex is rare