Although there are many varieties within each group, there are two main types of Japanese noodles: those made from buckwheat (soba) and those made from wheat (udon and somen). Since buckwheat requires cooler, drier growing conditions, the thin brownish-gray soba noodle is most popular in northern Japan. Udon, a thick, chewy beige wheat noodle, is favored in Kyoto and southern Japan. In winter, both types are most often enjoyed in hot broth either plain or topped with simmered vegetables.
In the summer, soba is commonly eaten cold with a chilled dipping sauce, but southerners prefer either hiyamugi or somen - thin, vermicelli-type wheat noodles in the summer. Traditionally, udon is not served cold.