The cooking broth that is used for boiling soba noodles makes a satisfying and heathy broth called Sobayu. It is usually served half way during the meal when you order cold soba at a soba noodle shop. The standard way to drink it is to pour the broth directly into the cup containing the dipping sauce. Usually, by the time they serve the broth, you would have used half the dipping sauce for the soba. The sobayu dilutes the dipping broth and makes a nice, not too salty broth. But I like to drink sobayu straight. It has a very clean taste and nice fragrance.
This sobayu has alight mustardy color because it is the cooking broth that came from boiling tartan soba noodles.