Japan-wide — horenso cultivation in all prefectures, peak quality in winter
Horenso (Japanese spinach, Spinacia oleracea — a winter-harvested variety) is one of Japan's most fundamental leaf vegetables, appearing in virtually every category of Japanese cooking. Unlike Western spinach varieties that are often wilted or sautéed, Japanese cooking has three primary preparations: ohitashi (blanched, squeezed, and dressed with dashi-soy sauce — the quintessential side dish); gomaae (blanched and dressed with sweet sesame sauce); and spinach as ingredient in tamagoyaki, miso soup, and nimono. The key technique is the thorough blanching followed by immediate cold-water shocking to preserve the vivid green colour, followed by squeezing out all water before seasoning (un-squeezed spinach dilutes sauces and creates a watery dish). Winter horenso (fuyu horenso), grown under snow or cold temperatures, is significantly sweeter than summer spinach due to the cold-weather accumulation of natural sugars as an antifreeze mechanism.
Vivid, slightly mineral green vegetable character; winter variety has pronounced natural sweetness; dashi-soy dressing elevates the natural flavour without masking it
Blanch in heavily salted boiling water (1% salt) for 30–60 seconds only; immediately transfer to ice water to shock and preserve colour; squeeze firmly between hands to remove all excess water before cutting or dressing; the bundle of squeezed spinach is then cut cross-wise into 3–4cm pieces; season ohitashi with dashi+soy (1:1 ratio) and serve at room temperature or lightly chilled.
Winter horenso's sweetness is remarkable — taste the blanched spinach before any seasoning and adjust soy downward if the natural sweetness is pronounced; gomaae sesame sauce benchmark: 4 tablespoons roasted black or white sesame + 2 tablespoons soy + 1 tablespoon mirin + 1 tablespoon sugar, all ground together in suribachi (Japanese mortar); the suribachi's ridged interior is ideal for grinding sesame to a paste; komatsuna (Japanese mustard greens) is often used interchangeably with spinach in ohitashi and has a more bitter-peppery character.
Under-blanching (spinach should be wilted but not mushy — typically 45 seconds in rolling boil); skipping the ice water shock (warm spinach continues cooking and loses vivid green); failing to squeeze out water thoroughly (dressed spinach becomes a watery mess within minutes); over-dressing with too much soy (ohitashi should be lightly flavoured, not strongly seasoned).
Japanese Cooking: A Simple Art — Shizuo Tsuji