Handmade flour. Slag noodles are made of refined white flour and auxiliary materials, which are repeatedly rubbed by hand to make fine water leaves, which are elastic and long in tendon, so they are handmade noodles. Flour is a kind of powder ground from wheat. According to the content of protein in flour, it can be divided into high gluten flour, medium gluten flour, low gluten flour and gluten-free flour.