Your food pipe or esophagus is surrounded by a muscular valve called the upper esophageal sphincter. This muscle only relaxes while swallowing, and during the other times, it contracts. The esophageal sphincter will have to relax momentarily when you burp to allow the built-up air to escape. When this doesn’t happen, it results in the inability to burp. This is why some people find it difficult to belch. It is also due to the lack of correct muscle memory; damage to the left part of the brain can be a cause for the inability to burp as well.