Brewing vessel

An unglazed or partially glazed earthenware pot used to boil coffee directly, most familiar as the olla de barro of Mexican café de olla. Clay heats and cools more slowly than metal, which suits a preparation that is simmered with sugar and spices rather than brought quickly to the boil. Whether the clay itself contributes flavour is widely claimed and not well evidenced; what it demonstrably does is hold heat.