A feature of the product is the burnt flavour that is derived from roasted unmalted barley, although this is a relatively modern development, not becoming part of the grist until the mid-20th century. For many years a portion of aged brew was blended with freshly brewed beer to give a sharp lactic flavour. Although the Guinness palate still features a characteristic "tang", the company has refused to confirm whether this type of blending still occurs. The draught beer's thick, creamy head comes from mixing the beer with nitrogen when poured.