Wheat hardness is a measure of how resistant wheat kernels are to being ground into flour — the physical toughness of the grain. Hard wheats fracture along the starch-protein boundaries, giving coarse particles with damaged starch that absorb more water and develop strong gluten: ideal for bread. Soft wheats shatter through the starch granules, giving fine, low-damage flour with weak gluten: ideal for cakes and biscuits. Millers measure hardness instrumentally to predict milling behaviour and flour performance, and breeders select for it deliberately. The single most important quality split in wheat — hard versus soft — traces back to this physical property and the puroindoline proteins that control it.