Achalasia is a digestive system disorder that makes it difficult to swallow food and liquids during eating and drinking. In a healthy swallowing process, the muscles of the esophagus contract rhythmically to push food towards the stomach (peristalsis). At the end of this process, the lower esophageal sphincter (LES), a ring of muscle between the esophagus and the stomach, relaxes to allow food to pass into the stomach. In patients with achalasia, this mechanism is impaired; the LES does not relax sufficiently, and the peristaltic movements in the esophagus weaken or completely cease. This condition is usually caused by damage to the nerve cells in the esophagus. Over time, the esophagus dilates and can completely lose its ability to propel food into the stomach. Consequently, food accumulates in the esophagus, may ferment, and can regurgitate into the mouth with a bitter taste.