Ash is another term for the mineral content of flour. When bakers are buying flour, they look at two important numbers in the flour’s description: the protein content and the ash content. The ash content is determined by burning a sample of flour in a controlled environment. The starch and protein, when burned completely, turn to carbon dioxide gas, water vapor, and other gases, but the minerals do not burn and are left as ash. In general, the higher the ash content, the darker the flour. This is because the bran and the outer parts of the endosperm contain more minerals than the whiter, inner portions of the endosperm. Similarly, whole-grain flour is higher in ash than white flour. In conventional baking, bakers like a relatively low ash content because it makes whiter breads. Today, many artisan bakers of handmade breads look for darker flour with a higher ash content because it makes breads with a more robust wheat flavor.
