Japan — tentsuyu developed alongside tempura in the Edo period (17th century), in the shokado (eating establishments near temples) and yatai (street food stalls) of Tokyo (then Edo). The standard ratio was codified through the Edo-period restaurant tradition and has remained largely unchanged since.
Tentsuyu (天つゆ) is the dipping sauce for tempura — a clean, light dashi-soy-mirin broth served hot alongside tempura, with finely grated daikon (大根おろし, daikon oroshi) and grated ginger placed separately at the edge of the dish. Tentsuyu's ratio and quality are as important as the tempura batter itself — a rough or poorly made tentsuyu undermines an otherwise excellent tempura. The sauce must be hot enough to prevent the tempura's crisply fried surface from going soggy on contact, clear enough to allow the dashi's quality to show, and precisely balanced so neither soy nor sweetness dominates. The daikon oroshi serves a dual purpose: it refreshes the palate between pieces and its natural diastase enzymes assist in digesting the tempura's oil.
Tentsuyu's flavour is a clean expression of dashi — the oceanic, mineral quality of kombu-katsuobushi extraction underpins a mild soy-sweet seasoning. Dipped briefly (not submerged), the tentsuyu's flavour applies a savoury-sweet gloss to the tempura's neutral fried exterior. The daikon oroshi's cool, slightly pungent freshness between pieces resets the palate for the next piece. The overall flavour experience: alternating between the warm, oily richness of the tempura and the clean, sharp brightness of tentsuyu with daikon — a rhythmic contrast that makes tempura eating a more sustained and varied pleasure than plain fried food.
Standard tentsuyu ratio: dashi 4 parts : mirin 1 part : soy sauce 1 part. For a lighter, Kyoto-style tentsuyu: dashi 5 parts : mirin 1 part : soy sauce 0.8 parts. Bring mirin to a boil first (to cook off harsh alcohol), then add dashi and soy; simmer briefly. The sauce must be served hot — cold tentsuyu soaks into the tempura coating rather than maintaining separation. The daikon oroshi is grated immediately before service (never pre-grated by hours); squeeze to remove excess moisture before plating. Ginger grate is optional but standard for fish tempura; omit for vegetable courses.
At Tempura Kondo (Tokyo, two Michelin stars), the tentsuyu changes subtly throughout the meal — slightly lighter for the delicate first courses, slightly richer for the more substantial prawn and seasonal vegetable pieces at the meal's centre. This progressive adaptation of the dipping sauce to the ingredients being served is a master-level refinement. Some tempura chefs add a small piece of kombu to the tentsuyu during service to maintain umami as the sauce cools and the diner works through their tempura.
Serving tentsuyu cold — cold sauce softens the tempura batter on contact, eliminating the textural contrast that defines the dish. Using low-quality dashi — tentsuyu is transparent; poor dashi is immediately apparent. Over-seasoning with soy — the sauce should taste of dashi first, with soy as a background seasoning. Serving daikon that was grated hours before — oxidised daikon turns bitter and discoloured.
Japanese Cooking: A Simple Art — Shizuo Tsuji; Tempura Didactic — Fumio Kondo (private monograph)