What are the causes of sour burps?

GERD versus burping?: Involuntary belching after a meal is normal, caused by release of swallowed gas after distension of the stomach with food. Magenblase syndrome is postprandial epigastric fullness & bloating, relieved by belching. Aerophagia (accumulation of gas due to air swallowing) is common with anxiety, hypersalivation from gum chewing, smoking, drinking, oral irritation. Both acid & bile reflux possible too.