Heartburn after drinking happens because of alcohol’s effect on the body’s physical functions, as well as the chemical reactions that happen in the stomach, according to Heartburn Remedies. When people drink alcohol, the lower esophageal sphincter relaxes and allows that acid to enter the tube. Too much caffeine causes the muscle that connects the stomach to the esophagus to relax, creating an opening for stomach acid to enter the esophagus causing acid reflux.