Tentsuyu (Authentic Tempura Dipping Sauce)

Tentsuyu began as street food. In the second half of the Edo period (1603-1868), rapeseed oil became cheap and plentiful, so tempura stalls popped up all over Edo. Vendors deep-fried small pieces of seafood on skewers in oil. Customers ate them standing up. A skewer cost about ¥100 in today’s money. There was no individual bowl of sauce. A single large bowl sat on the stall. People dipped their skewer in, added grated daikon, and ate. The thick, dark, heavy batter from the stall fire needed cutting, so the light dashi-forward broth and sharp daikon did exactly that. The character of tentsuyu was set right there.

My ratio is 5 parts dashi to 1 part mirin to 1 part koikuchi soy sauce. That is 1 extra measure of dashi compared with the common 4-1-1 standard. More dashi lowers the relative strength of the soy sauce and mirin. I never add sugar. The natural sweetness of mirin is enough, and extra would push sweetness forward. I also skip citrus. 2 strong aromas would fight and the dashi would lose. In Kansai some cooks blend in light-colored (usukuchi) soy sauce, but I stick to dark only. Of course you can use the light-colored kind if you prefer. My last step is to drop in a small handful of bonito flakes after I remove the pot from the heat. The flakes give aroma without clouding the broth or adding any sourness.

Oigatsuo is the second handful of bonito flakes you drop in after the dashi is already finished. The word itself means chasing the bonito. Its job is different from the first steep. That first pull spends time moving umami into the water. This one puts aroma on top. Aroma is the first thing heat and time strip away, so the longer the flakes sit the thinner the smell becomes. I add them only after the heat is off and lift them the moment they begin to sink. The umami is already in the pan. What goes in now is the part that reaches the nose.

A nel cloth is cotton flannel, brushed on one side, and in Japan it is what people reach for to strain dashi and coffee. The 3 ways of straining listed in this step land at slightly different levels of clarity. The weave of a nel cloth is fine enough to catch the bonito particles a sieve alone lets through, and the sauce comes out a step clearer for it. Cheesecloth gets close once you fold it over a few times. A paper towel is in every kitchen and strains it plenty clear. Use whichever one you own.

A salty tsuyu comes from over-reducing it or from too much soy sauce, since water leaves the pan over the heat and the salt left behind reads stronger for it. Add more dashi (liquid) to loosen it, and if the sweetness thins out along with it, return a few drops of mirin. A flat tsuyu has a different cause, which is a weak dashi. Brew a stronger one and stir a little of that in, and the tsuyu lifts back up right there in the bowl. From the next batch, drop the heat the moment it boils, count 1 minute, and take the pan off there.

Either the tsuyu was too hot, or the piece of tempura sat in it for too long. The inside of a fried coating is a mesh of fine holes left behind where the water escaped, and those holes pull hot liquid in faster than cool. If the pan is still hot, pour the tsuyu into the dipping bowl and wait until the steam disappears. Dip just the corner of the piece and eat it right away.

The alcohol in the mirin has yet to cook off. If you start counting before the pan is truly boiling, the minute passes without the liquid ever getting there, and the sharp edge of the alcohol stays in the finished tsuyu. To fix the pan in front of you, put it back over low heat and wait until the smell turns sweet, then add dashi to replace what evaporated so the strength holds. Next time, watch for the dashi and mirin to reach a real boil first, then lower the heat and start counting there.