Custard is usually cooked in a double boiler (bain-marie), or heated very gently in a saucepan on a stove, though custard can also be steamed, baked in the oven with or without a water bath, or even cooked in a pressure cooker. Custard preparation is a delicate operation, because a temperature increase of 3-6 °C (5–10 °F) leads to overcooking and curdling. Generally, a fully cooked custard should not exceed 80 °C (176 °F); it begins setting at 70 °C (158 °F). A water bath slows heat transfer and makes it easier to remove the custard from the oven before it curdles.