Japanese noodles, whether udon or these buckwheat-flour ones, are often served in broth
... 
served in noodle soups like udon, they are most often served cold in... [DOC] [TLE] Japanese Noodle Recipes, Soba, Udon, Somen & Ramen recipes [PAR] Soba is made of buckwheat flour, and can be eaten hot, in soup, or cold, with 
dipping ... For hot soba, prepare the soup stock separately from the noodles, and 
serve hot.