Sōmen (Japanese: 素麺), somyeon (Korean: 소면), or sùmiàn (simplified Chinese: 素面; traditional Chinese: 素麵) are very thin noodles made of wheat flour, less than 1.3 mm in diameter. It is used extensively throughout East Asian cuisines. The most common example is Japanese somen and the noodles are usually served cold with soy sauce and dashi dipping sauce, similar to mori-soba (盛り蕎麦) noodles style. There are no academic study nor evidence of where the somen originally invented. The difference between somen and another thin Japanese noodles hiyamugi (冷麦) are, hiyamugi is sliced by a knife to make them thin noodles but somen noodles are thinned by stretching the dough. The dough is stretched with the help of vegetable oil to make very thin strips and then air dried. When served warm in soup, usually in winter, they are called nyumen (煮麺) in Japanese.
Sōmen are usually served cold with a light flavored dipping sauce or tsuyu. The tsuyu is usually a katsuobushi-based sauce that can be flavored with Japanese bunching onion, ginger, or myoga. In the summer, sōmen chilled with ice is a popular meal to help stay cool.
Sōmen served in hot soup is usually called nyūmen and eaten in the winter, much as soba or udon are.
Some restaurants offer nagashi-sōmen (流しそうめん flowing noodles) in the summer. The noodles are placed in a long flume of bamboo across the length of the restaurant. The flume carries clear, ice-cold water. As the sōmen pass by, diners pluck them out with their chopsticks and dip them in tsuyu. Catching the noodles requires a fair amount of dexterity, but the noodles that are not caught by the time they get to the end usually are not eaten, so diners are pressured to catch as much as they can. A few luxury establishments put their sōmen in real streams so that diners can enjoy their meal in a beautiful garden setting. Machines have been designed to simulate this experience at home.
Sōmen (in large white bowl at upper-right) with assorted toppings
In Korean cuisine, somyeon is used in hot and cold noodles soups such as janchi-guksu (banquet noodles) and kong-guksu (noodles in cold soybean soup), as well as soupless noodle dishes such as bibim-guksu (mixed noodles). It is often served with spicy anju (food that accompanies alcoholic drink) such as golbaengi-muchim (moon snail salad).