Probably because just after eating sugar or food with high sugar content, there are still lactic acid bacteria in the mouth, sweet food by fermentation and the formation of lactic acid, sweet food will also increase the secretion of stomach acid, so the mouth will be sour after eating. The secretion of stomach acid and saliva increases after getting cold, and saliva and stomach acid break down the starch in the mouth into sugar, which also forms acid after fermentation. It may also be caused by indigestion, stomach fire, inadequate digestion of food accumulates in the body to form toxins, causing bad taste in the mouth. It may also be caused by stomach diseases such as gastritis or peptic ulcer; suffering from oral diseases can also trigger sourness in the mouth after eating. It is recommended to develop good personal hygiene habits, rinse your mouth or brush your teeth after eating, try not to eat raw and cold food, don’t eat sweets and cold drinks together, eat more easily digestible food, eat less greasy, spicy food, etc. If you suffer from oral diseases, you should seek medical attention in time.