Tteok is largely divided into four categories: steamed tteok (찌는 떡), pounded tteok (치는 떡), boiled tteok (삶는 떡) and pan-fried tteok (지지는 떡). The steamed tteok is made by steaming rice or glutinous rice flour in a siru (시루), a large earthenware steamer, so it is often called sirutteok (시루떡). It is regarded as the basic and oldest form of tteok. Pounded tteok is made by using a pounding board or mortar after steaming it first. In making pan-fried tteok, the rice dough is flattened like a pancake and pan-fried with vegetable oil. Shaped tteok are made by kneading dough with hot water, then shaping it into balls.