Ponzu

Steps

1. zest5 min
   vegetable peeler, wide strips, no white pith — substitute-citrus branch only
   lemon, peeled in wide strips before it is juiced, taking only the coloured layer. This step belongs to the substitution and not to the tradition: yuzu carries a floral, resinous perfume that no lemon has, and since most of any citrus's aroma sits in oil glands in the peel rather than in the juice, steeping the peel is the documented way to recover some of the difference. Skip it entirely if you have real yuzu, sudachi or kabosu — the traditional formulations use juice alone and the added peel would muddy them. Take no pith: pith carries no aroma oil and contributes only bitterness, which a sauce steeping overnight has plenty of time to extract
2. mix8 min
   sanitised glass jar, cold, solids pushed under the liquid
   soy sauce + lemon juice + lime juice + mirin + rice vinegar, combined in a clean jar, then + kombu + katsuobushi + the lemon peel, pressed below the surface. Wipe the kombu with a dry cloth rather than rinsing it: the white bloom on the surface is mannitol and free glutamate, which is most of what the kelp is here to give, and washing it off is washing away the umami. Use nikiri mirin — mirin that has been boiled to drive off its alcohol — or boil ordinary mirin and cool it first, because nothing in this recipe is ever heated and raw alcohol will sit in the finished sauce with nothing to cook it away. For the same reason use true hon-mirin rather than a corn-syrup seasoning: there is no cooking here to hide it. The jar must be scrupulously clean, since this is a cold, uncooked preparation that will sit for weeks
3. infuse720 min
   refrigerated, sealed, 12 to 24 hours (up to 3 days)
   the filled jar, refrigerated and left alone. This is the whole method and the reason ponzu is worth making rather than buying: kombu releases glutamate and katsuobushi releases inosinate, and those two umami compounds are synergistic — together they read many times more savoury than the arithmetic of either alone. Cold extraction is slow but selective, pulling the savoury amino acids and nucleotides while leaving behind the bitter alginates and the sharp fishiness that heat would drag out of the same ingredients in minutes. That is why nothing is cooked. Thirty minutes already gives a usable sauce and the depth keeps building for days; overnight is the practical centre of the sources. Do not shake it — agitation abrades the bonito flakes and clouds the sauce
4. clarify5 min
   fine-mesh sieve or muslin, solids never pressed
   the steeped liquid, poured through a fine sieve and the kelp, bonito and peel discarded. Straining is a required step and not a refinement. Left in, kombu goes on releasing alginates and turns the sauce viscous and faintly slimy, and the bonito breaks down into a muddy sediment that makes a clean savoury sauce taste of old fish. Let it drain rather than pressing or wringing the solids: squeezing forces fine particles and the bitter compounds through the mesh, and clarity is most of what separates a good homemade ponzu from a cloudy one
5. store5 min
   sanitised airtight bottle, refrigerated 1 to 2 months
   strained ponzu, bottled and refrigerated, where it keeps a month or two and improves over the first weeks as the flavours marry. Sources claim anywhere from two weeks to a year and the honest window for a home kitchen is the shorter end of that: the sauce is salty and acidic enough to resist spoilage but the citrus aroma fades steadily, so a six-month bottle is safe and dull. Freeze it in an ice-cube tray for longer keeping. Serve it as a dipping sauce for shabu-shabu, tataki, gyoza and cold tofu, or thinned with a little dashi for a dressing