(Pseudo)cereal grains have been the basis of human nutrition for thousands of years. The various types of cereals are usually harvested by grain harvesters and must be technologically processed in different ways before consumption. In addition to genotype and growing conditions, the compositional characteristics of the (pseudo)cereal grains are highly dependent on the processes used. In the present study, the effects of hulling, cleaning and brushing/polishing wheat, spelt, oat, barley, common and Tartary buckwheat grains and their fractions on physical parameters (thousand kernel weight, kernel width, fractional yield) and nutritional characteristics (protein, fat, β-glucan, macro- and microelements) were investigated. Grain samples contained 22.7–148.5 mg/g protein, 4.5–69.6 mg/g fat and 0.5–54.4 mg/g β-glucan. The content of macro- (K, Mg, P, S, Ca) and microelements (Mn, Fe, Zn, Na, Cu, Cr, Mo) varied considerably among the studied (pseudo)cereals and their grain fractions. Analysis of variance showed that species and fractions significantly influenced most of the analyzed characteristics. However, the composition of the edible fractions was not significantly dependent on the brushing/polishing process.