The following are some of the causes of beer diarrhea: 1. The patient may have enteritis or gastritis, and although the beer is low, it also contains ferments and alcohol, so when the beer comes into contact with the gastrointestinal mucosa, it will stimulate the mucosa, which is already inflamed, and produce diarrhea. 2. The symptoms of diarrhea will occur when the bacteria enter the digestive tract and stimulate the permeability of the mucosa. 4.