Although apples contain metal elements such as zinc and iron, but after all, they are not monomers, so they do not react with stomach acid to produce gas.
The so-called acidic and alkaline food, not by the taste or smell to identify, mainly to see the food is absorbed by the body after oxidation of the chemical elements contained as the basis for identification. All contain nitrogen, sulfur, phosphorus and other non-metallic elements are more acidic food, while sodium, potassium, calcium, magnesium and other metal elements are more alkaline food. Not acidic flavor is acidic food, such as vinegar is acidic, citrus, plums, apricots and other fruits are also acidic, but they are not acidic food, on the contrary, is a typical alkaline food. Another example is grain, candy, pastries, fish, pork and other animal meats, etc., is not alkaline food, all belong to the acidic food.