There's no secret about it,
somen,
hiyamugi, and
udon are all
Japanese noodles made from the same ingredients of
flour and
salt water, practically made in the same manner when mass-produced.
Only thickness differentiates any type from the other two, according to the Japanese Agricultural Standards (
JAS):
somen: less than 1.3 mm in width
hiyamugi: 1.3 - 1.7 mm in width
udon: 1.7
mm and above
Somen basically look and taste like
angel hair noodles. Served cold in somen
tsuyu soup, it is a popular summer dish. A variety of toppings exist, which may include but are not limited to
nori seaweed, roasted
sesame seeds,
cucumber slices, chopped
negi, stir-fried
egg slices,
ham slices, ginger, ground wasabi, and
tomato slices. (However, traditional somen aren't supposed to have toppings like
hiyamugi.)
Nagashi somen
Participants carry around a bowl with soup and toppings, waiting at a
bamboo waterslide. One person serves the prepared cold somen noodles from the top of the bamboo
waterslide by releasing small amounts at a time, while participants scoop out
their share from the slide with
chopsticks.