Make it once, then just dilute
Kaeshi and the noodle broths
The figure
Kaeshi 5 : 1 : 1
Kaeshi is soy 5 : mirin 1 : sugar 1. Change only how much dashi you dilute it with, and every noodle broth follows.
What kaeshi is
A soba shop does not build its broth one bowl at a time. It cooks soy, mirin and sugar together, lets it rest, and keeps the concentrate. That is kaeshi. Everything after it is dilution — the cold dip, the hot broth, the tempura dip.
Soy 5 : mirin 1 : sugar 1. The edge comes off the soy while it rests.
The dilution
How much dashi goes against 1 part kaeshi — that single number decides the dish. Cold broths are strong, hot ones weak, because cold blunts the tongue to salt.
- Dipping broth (mori, zaru) — kaeshi 1 / dashi 3–4
- Hot broth (noodles in soup) — kaeshi 1 / dashi 7–9
- Tentsuyu — kaeshi 1 / dashi 5
- Oden — kaeshi 1 / dashi 5
Making it
Hon-gaeshi: boil off the mirin's alcohol, melt the sugar into it, add the soy and stop the heat around 80°C. Never boil it. Cool it and let it rest one week to one month.
Nama-gaeshi: no heat at all. Dissolve the sugar and mirin into the soy and let it rest. More aroma survives. This is the one for a hurry.