Koshun

Koshun is a Shizuoka sencha cultivar bred for one trait above the rest: an orchid-like floral aroma that its own release material describes as unmistakably different from Yabukita’s, and that difference was the entire point. Crossed in 1970 from two locally-bred aroma cultivars, Kurasawa and Kanayamidori, and registered in 2000, it belongs to a run of late-twentieth-century Shizuoka cultivars bred not to replace Yabukita at scale but to give individual growers something distinctive to sell under their own name. It has become one of the more commercially interesting aroma cultivars to come out of the prefecture, sold as single-cultivar sencha, pan-fired kamairicha and, at specialist shops, a withering-style black tea.

Lineage

• Kurasawa (くらさわ) ♀ — an unregistered 1967 selection made at the same Shizuoka station, chosen from naturally-pollinated Yabukita seedlings rather than a deliberate cross. Its trial designation was Shizu-7111, and it belongs to a loosely-grouped “7000 series” of Yabukita-derived Shizuoka selections from the same years, alongside Yamakai, Suruga-wase and Fuji-midori. It contributes a forest-like, woodland aroma and a fairly heavy astringency of its own, and — as matcha — a distinctive cocoa note.
• Kanayamidori (かなやみどり) ♂ — 茶農林30号, bred not at the prefectural station but at the national tea experiment station at Kanaya, and registered in 1970 from a 1949 cross of a zairai selection (S6) as seed parent with Yabukita as pollen parent. It contributes the other half of the aroma-forward pairing: a cultivar known for a sweet, milky fragrance closer to fresh dairy than to anything in the standard vocabulary of green tea.

This is a controlled cross rather than a landrace selection, but an unusual one in that neither parent is itself a fully “clean” cultivar in the pedigree sense. Kurasawa was picked out of an open-pollinated seedling population, so its own pollen parent is unrecorded; Kanayamidori is a proper controlled cross, but one generation removed from Yabukita on its own account. The result is that Koshun carries Yabukita in its background on both sides — through Kurasawa directly, and through Kanayamidori’s paternal line — even though it was selected for and is prized precisely for smelling nothing like it. No cultivars bred using Koshun as a parent in turn have been located in the course of this research.

History

Kurasawa and Kanayamidori both belong to a documented wave of Shizuoka cultivar selection spanning the mid-1960s to mid-1970s, driven by surging domestic demand and the growing scale of tea-processing machinery, with breeding aimed at higher-yielding, differently-timed, higher-quality cultivars. Koshun’s own cross was made in 1970 at the Shizuoka Prefectural Tea Experiment Station, using Kurasawa (itself only three years out of selection) as the seed parent and the newly-registered Kanayamidori as the pollen parent.

The chronology from there is unusually well documented for a Shizuoka prefectural cultivar:

• 1970 — crossed: Kurasawa × Kanayamidori.
• 1978 — entered clonal (vegetative) comparison trials under the strain name 70-11-6.
• 1987 — entered the prefecture’s recommended-cultivar determination trial.
• 1995 — breeding formally completed (育成).
• 1996 — application filed on 21 October for registration under the Seed and Seedling Law (種苗法) as application No. 9199, under the cultivar name Koshun; published 12 March 1999.
• 2000 — registered on 27 June as 品種登録第8131号.

That is a thirty-year span from cross to registration, and it is worth being precise about the gap between 1996 and 2000: the earlier date is when the registration application was filed, not when it was granted, and at least one secondary source conflates the two by describing 1996 as the registration year. The station’s own material and independent registry listings agree on 2000 as the year Koshun was actually registered.

Koshun was one of two flagship releases — alongside Tsuyuhikari — of a broader shift the station’s own retrospective frames explicitly: from the Showa-era priorities that had produced Kurasawa and Kanayamidori (yield, timing, mechanisation) to a Heisei-era one, prompted by the end of the bubble economy and a more diversified market, of breeding “cultivars distinguished by flavour”. The framing given for Koshun specifically sets out three intended shifts: from undifferentiated cultivars toward branding, from shared co-operative processing factories toward growers who cultivate, process and sell their own leaf, and from the mass market toward a niche one.

An aroma the industry wasn’t yet built for

The same retrospective is candid about the problems Koshun posed during development, and they are worth keeping alongside the flattering description of its aroma. Because it buds in the same mid-season window as Yabukita, it did nothing to ease the scheduling pressure a shared processing factory faces at peak harvest — unlike an early or late cultivar, it competes for the same capacity rather than spreading it. Its buds are numerous but small and harden quickly, a habit poorly suited to mechanised harvesting. It was judged short on umami and fairly astringent. And above all, its aroma was strong and entirely unlike Yabukita’s, at a time when Yabukita was effectively the industry’s quality standard and anything that smelled different from it was read as a fault rather than a feature — the same reception Kanayamidori’s milky aroma had met a generation earlier. Koshun’s eventual success rests on that expectation having shifted by the time it reached the market.

A retrospective article on Koshun published in the trade magazine 月刊「茶」 (Shizuoka Prefecture Tea Council) and reproduced by O-CHA NET is credited to 中村順行, a researcher associated with the cultivar’s development and later with a University of Shizuoka group that has continued to publish on it.

Characteristics

Koshun is plucked medium (中生), in the same window as Yabukita rather than distinctly earlier or later — the registration filing rates its budding slightly early (ほう芽期やや早) and only its plucking date mid-season — a deliberate trait of the cross, though one that, as above, was seen as a limitation rather than an advantage when the cultivar was new. The tree is vigorous with an open, spreading habit, which makes it easy to train while young; as a garden matures its bud-number tendency strengthens, and growers are advised to plan renewal pruning to keep yield up. Reported yield is high, particularly from young bushes, and higher than Yabukita’s. Cold resistance is strong enough that it is recommended across the whole of Shizuoka Prefecture, but it is susceptible to Kuwashiro scale insect (white peach scale) and needs careful pest control; one vendor source adds that it resists anthracnose slightly better than Yabukita but is weak against bacterial shoot blight, though this has not been corroborated elsewhere. Processed leaf rolls finely and holds a uniform shape.

The cup is the reason the cultivar exists, and the sources are consistent on its character even where their vocabulary differs. Shinkoju, the single-cultivar specialist that stocks it, describes its defining trait plainly as a “characteristic orchid-like aroma” (蘭のような特徴的な香り). The breeding station’s own sensory work is more specific still: panellists describing Koshun’s withering aroma (萎凋香 — the fragrance drawn out by a withering step in processing) reached for rose-like sweet floral notes, milkiness and fruitiness, and reported that the aroma intensifies with longer withering; the two aroma compounds singled out in that work are geraniol, associated with fresh rose, and linalool oxide IV. Consumer preference panels rated Koshun highly for aroma quality, taste intensity and umami, with younger women in particular describing the aroma as fresh and cool. Retail tasting notes from Shinkoju’s own product lines add shiso and cherry-leaf notes in lightly-steamed sencha, apple-candy in one black tea grade, and honey with fruit in a premium black tea. Set against this, the tea is only moderately umami-rich and can read as fairly astringent, particularly in the finish — a trade the breeding programme itself acknowledged rather than concealed.

Processing favours that aroma over body: deep steaming (fukamushi) is explicitly discouraged, since it blunts the fragrance that is the cultivar’s whole appeal, and growers are advised to extend steaming only slightly, and only as far as needed to soften astringency, before the aroma starts to suffer. Standard steaming produces a bright yellow liquor with a long finish. Koshun also takes well to pan-firing: in a 2006 sensory panel comparing kamairicha made from Koshun and from Yabukita, Koshun scored markedly higher for first-flush aroma. Its readiness to develop a strong withering aroma has also made it a candidate for withering-based processing outside plain sencha, and it is sold in that form — as a black tea with a honeyed, fruity character — by at least one specialist retailer, alongside its more usual sencha and kamairicha. Recorded plantings are small: one Shizuoka prefectural dataset puts Koshun at 12 ha against 139 ha for Tsuyuhikari, its contemporary from the same breeding shift, which places it as a boutique rather than a mainstream cultivar even within its own prefecture.