Soba is the Japanese name for buckwheat. It is synonymous with a type of thin noodle made from buckwheat flour, and in Japan can refer to any thin noodle (unlike thick wheat noodles, known as udon). Soba noodles are served either chilled with a dipping sauce, or in hot broth as a noodle soup. It takes three months for buckwheat to be ready for harvest, so it can be harvested four times a year, mainly in spring, summer, and autumn. In Japan, buckwheat is produced mainly in Hokkaido. Soba that is made with newly harvested buckwheat is called "shin-soba". It is sweeter and more flavorful than regular soba.
In Japan, soba noodles are served in a variety of settings: they are a popular inexpensive fast food at railway stations throughout Japan, but are also served by expensive specialty restaurants. Markets sell dried noodles and men-tsuyu, or instant noodle broth, to make home preparation easy.
Some establishments, especially cheaper and more casual ones, may serve both soba and udon as they are often served in a similar manner. Soba is the traditional noodle of choice for Tokyoites. This tradition originates from the Tokugawa period, when the population of Edo (Tokyo), being considerably wealthier than the rural poor, were more susceptible to beri beri due to their high consumption of white rice, which is low in thiamine. It was discovered that beri beri could be prevented by regularly eating thiamine-rich soba. In the Tokugawa era, every neighborhood had one or two soba establishments, many also serving sake, which functioned much like modern cafes where locals would stop for a casual meal.
Udon is a type of thick wheat flour noodle of Japanese cuisine. Udon is often served hot as a noodle soup in its simplest form, as kake udon, in a mildly flavoured broth called kakejiru, which is made of dashi, soy sauce (shoyu), and mirin. It is usually topped with thinly chopped scallions. Other common toppings include tempura, often prawn or kakiage (a type of mixed tempura fritter), or aburaage, a type of deep-fried tofu pockets seasoned with sugar, mirin, and soy sauce. A thin slice of kamaboko, a halfmoon-shaped fish cake, is often added. Shichimi can be added to taste.
The flavor of broth and topping vary from region to region. Usually, dark brown broth, made from dark soy sauce (koikuchi shoyu), is used in eastern Japan, and light brown broth, made from light soy sauce (usukuchi shoyu), is used in western Japan. This is even noticeable in packaged instant noodles, which are often sold in two different versions for east and west.