Tarhana is the traditional Turkish version of kishk: a fermented wheat flour-yoghurt mixture dried and used in soups. Yoghurt, flour, and often vegetables and herbs are fermented for several days, then dried and crumbled into a shelf-stable powder that reconstitutes into a tangy, nourishing soup, the Greek version being known as trahanas. The lactic fermentation preserves the mixture and develops its characteristic sour flavour while improving digestibility. It is one of the world’s oldest instant foods, a peasant staple that keeps for months without refrigeration.