Japan — shun concept documented from at least the Heian period (794–1185); formalised in kaiseki through the 24 solar terms (nijushi sekki) calendar alignment; encoded in Japanese poetic culture (seasonal reference words, kigo, in haiku)
Shun (旬) — the concept of ingredients being at their peak seasonal perfection — is the organising philosophy of Japanese cuisine. Rather than a theory imposed on cooking, shun is an empirical observation of when each ingredient achieves its maximum sugar content, minimum water content, optimal fat accumulation, or most complex aromatic development. The Japanese seasonal calendar for food is extraordinarily detailed: spring (haru, March–May) brings bamboo shoots, young fish (hatsu-gatsuo skipjack tuna), wild mountain vegetables (sansai), cherry blossoms, and the first bonito; summer (natsu, June–August) brings unagi eel (Doyo no Ushi no Hi), ayu sweetfish, myoga, edamame, corn, and cold noodle culture; autumn (aki, September–November) brings the peak of the calendar — matsutake mushrooms, sanma Pacific saury, kuri chestnuts, nashi pears, and the season's best sake (hiyaoroshi); winter (fuyu, December–February) brings crab, oysters, oden, fugu pufferfish, and the richest fatty fish.
The philosophy that produces the flavour — shun determines which ingredients reach the kitchen and when, making seasonality the first and most important decision in Japanese cooking
Shun is dynamic — it changes week by week, not just season by season. A chef at the peak of their craft knows not just that bamboo shoots are spring vegetables but that the first bamboo shoots in March from Kyushu are sweeter and more delicate than the April bamboo from Kyoto, which are firmer and more complex. The transition days (sekki, the 24 solar terms from the traditional lunisolar calendar) are used by serious Japanese cooks to calibrate seasonal transitions precisely. Ingredients eaten slightly before their peak (hashiri, 'running') are prized for their delicacy and freshness; ingredients at the exact peak (shun) are consumed for maximum character.
Build a personal shun calendar by visiting a good Japanese fishmonger and produce market weekly — what the vendor is excited about is usually the current shun ingredient. The Japanese concept of 'ichiju sansai no shun' — all components of the meal reflecting the same season simultaneously — is the target. Restaurant menus that change daily (日替わりランチ, daily changing lunch) are the best way to eat shun in Japan. Learn the kanji for the major seasonal ingredients to navigate market purchases.
Treating Japanese seasonal eating as merely decorative — it is a flavour-improvement system, not symbolism. Ignoring the sub-regional and microclimate dimensions of shun — the first sanma arrives in Hokkaido in September; the same fish doesn't reach Tokyo until late September or October. Substituting imported or greenhouse-grown ingredients when the seasonal product isn't available — better to choose a different dish appropriate to the season than to use an out-of-season substitute.
Murata, Yoshihiro — Kaiseki; Tsuji, Shizuo — Japanese Cooking: A Simple Art; UNESCO Washoku documentation