Kidney is the edible kidney of cattle, sheep or pigs, a firm, dense offal organ with a smoothly lobed surface and a deep, distinctly minerally, faintly ammoniac savour. Beef (ox) kidney is large and multi-lobed; lamb kidney is small, tender and mild; pork kidney sits in between. It is the classic partner to steak in steak-and-kidney pie and the star of French rognons.