Definition: "In simple terms structured proteins are considered to be collagen, elastin and keratin and all others as non-structured. Collagen is the leather making protein and needs to be protected in process whilst keratin (hair / epidermis) is removed in liming and elastin is modified during soaking, liming and bating. Non-structured proteins exist between the collagen structures and need to be removed during soaking and liming to improve diffusion of process liquors and to enable the production of mellow, flexible leather with well opened fibres."