Unkai

Unkai is a kamairicha (pan-fired) cultivar bred at the Miyazaki Prefectural Agricultural Experiment Station and registered in April 1970 as Cha Norin No. 29. It was bred to solve a specific regional problem: three kamairicha cultivars were already registered and in use across Kyushu — Takachiho, Izumi and Yamanami, the first and last from Miyazaki itself and Izumi from the Kyushu Agricultural Experiment Station — and each had a documented weakness, in regional adaptability, disease resistance and quality respectively. Unkai’s brief was to beat all three, and Yabukita besides, on yield, disease and cold resistance, and pan-fired cup quality at once. It is the pollen parent of Minekaori (Yabukita × Unkai, 1988/1990), which is now the better known of the two.

Lineage

• Takachiho ♀ — the seed parent, itself a single-plant selection made in 1924 from Miyazaki zairai (native, seed-grown) stock under the working name Miyazaki No. 9, and registered in its own right in 1953. It contributed Unkai’s regional adaptation to Miyazaki’s kamairicha districts, though its own adaptability outside them was rated a weak point.
• Miya-F1 9-4-48 ♂ — an unnamed F1 breeding line, not a released cultivar. The 1971 release paper’s pedigree chart identifies it as the product of a 1934 cross between MA23, an accession the station held as “宮崎アッサム種” (Miyazaki Assam variety, i.e. Camellia sinensis var. assamica), and MC3, recorded as “宮崎コーカサス種” (Miyazaki Caucasus variety). Neither MA23 nor MC3 was itself a named cultivar — they were pre-war germplasm accessions kept at the station for breeding stock.

This is a controlled cross, not a landrace selection, but one generation removed on the female side from exactly that: Takachiho was itself a zairai pick. What makes the cross unusual is the pollen side. Most registered Japanese tea cultivars trace to Camellia sinensis var. sinensis alone; Unkai carries var. assamica ancestry through MA23, two generations back. Whether that shows up in the cup is not something the release paper investigates directly, but Unkai’s own quality scores in the pan-fired evaluation were high, and its offspring Minekaori — Yabukita × Unkai — is one of the very few other kamairicha-specific registered cultivars in Japan, recommended for the same Miyazaki districts (Gokase, Takachiho) that Unkai itself grows in.

History

The cross was made in 1952 at what was then the Miyazaki Prefectural Agricultural Experiment Station’s Kawaminami Branch (川南分場), using Takachiho — at that point still going by its pre-registration name Miyazaki No. 9 — as the seed parent and F1 9-4-48 as the pollen parent. By the time the cultivar was released nearly twenty years later, the branch had been reorganised into the Tea Research Branch of the Miyazaki Prefectural General Agricultural Experiment Station.

Selection was slow, as it is for most tea cultivars. In 1958 the F1 population from the 1952 cross was brought into a designated tea-breeding trial and characterised; that year one individual passed a first round of selection, and in 1959 it passed a second round and was given the individual number A15. From 1960, A15 was carried forward into systematic comparison trials against Takachiho under that strain name, and from 1963 its quality was assessed alongside yield surveys using a small-batch processing method (2 kg of fresh leaf per test). Regional-adaptability trials followed from 1962 at the Kumamoto and Shizuoka prefectural tea experiment stations and at the Miyazaki station’s own cold-land cultivation section, joined from 1965 by the Ministry of Agriculture and Forestry’s national Tea Experiment Station and by Miyazaki’s Miyakonojō tea management farm.

The results were strong across the board: growth and yield markedly ahead of Takachiho, no weak point in disease or cold resistance, good quality as pan-fired tamaryokucha, and good results at the Kumamoto trial site too — evidence of exactly the regional adaptability Takachiho had lacked. On the strength of that record, A15 was taken up as a recommended cultivar in Kumamoto and Miyazaki from 1969, and in April 1970 it was formally named and registered as Unkai, Cha Norin No. 29. The release paper itself — Sameshima, Yonemoto, Mukai, Hirakawa, Maso, Nagatomo and Tokunaga, “A Newly Registered Tea Variety ‘Unkai’ for Green Tea,” Chagyo Kenkyu Hokoku No. 35, 1971 — closes with a short section on the name: it stands for the fresh 雲海 of the mid-mountain kamairicha districts of Kumamoto and Miyazaki where the cultivar was to be promoted as a recommended variety, with the added sense of spreading like the clouds.

Why pan-fired, and what that means

Kamairicha (釜炒り茶) is defined by how the leaf is killed-green: not steamed, as sencha, gyokuro and tencha are, but roasted in a heated iron pan or drum. Steaming is the method China’s Song dynasty passed to Japan; pan-firing is usually said to have arrived later, in the Ming period, though no primary source actually confirms that route, and it may equally have reached Kyushu via other channels at the end of the Sengoku period — one tradition credits Chinese potters who settled near Ureshino in the mid-15th century. Whatever the route, it took root specifically in Kyushu, chiefly in Saga and Nagasaki (Ureshino tea) and in Kumamoto and Miyazaki (Aoyagi tea), and it is the region Unkai and its kin were bred for.

The processing difference shows up directly in the leaf and the cup. Because the leaf is stirred and roasted rather than steamed and dried flat, kamairicha rolls into a rounded, comma-like shape (勾玉, magatama) instead of sencha’s straight needle, which is also why kamairicha is classed as a style of tamaryokucha (玉緑茶, “curled/ball green tea”). Pan-firing drives off less chlorophyll-linked bitterness than steaming does, so the liquor runs paler and the astringency softer, while the dry roasting itself contributes a toasted, faintly nutty aroma that steamed teas don’t have. It is this specific style — かまいり製玉緑茶, pan-fired tamaryokucha, as opposed to the steamed tamaryokucha (“guricha”) also made elsewhere in Japan by simply skipping the final shaping step — that Unkai’s release paper evaluates it against.

Characteristics

Unkai has an intermediate bush form with vigorous, well-branched growth and a large spread. Its mature leaves are slightly smaller than Yabukita’s but slightly larger than Takachiho’s, a medium oval shape with little waviness at the margin; the leaf surface is dark green, glossy and smooth. Bud length at picking is longer than Takachiho’s, and young leaves are round, glossy and only lightly tinged with anthocyanin.

It is a medium-season cultivar. Averaged over the 1964–69 trial years, budding fell on 2 April against Takachiho’s 29 March and Yabukita’s 31 March — about two days later than Yabukita — while first-flush picking landed on 5 May, the same date as Yabukita and one to three days earlier than Takachiho, depending on the year. Growth is vigorous from the first years after planting, and yield is high: field trials against Takachiho (the direct benchmark, since Unkai was bred to supersede it) showed roughly 150% of Takachiho’s yield three to five years after planting, settling to about 115–130% by years six to nine. Hundred-bud weight runs slightly lighter than Takachiho’s despite the higher bud count.

Cold and disease resistance are Unkai’s clearest advantages over both comparison cultivars. In field frost-damage surveys and in cutting-based freezing tests at −15°C to −17°C it came out ahead of both Takachiho and Yabukita, and at the cold-highland trial site the on-site judgement rated it 極強 (very strong) for cold resistance and 強 (strong) for disease resistance, against Takachiho’s 強 and 中 (medium) and Izumi’s 中 and 弱 (weak). It showed no notable susceptibility to mochi disease, anthracnose or the dieback symptoms tracked in the trial, with clearly less anthracnose than either comparison cultivar. Propagation by cuttings is as easy as for Takachiho or Yabukita, with good survival and vigorous growth after rooting.

In the cup, processed as pan-fired tamaryokucha, Unkai’s release paper describes good compactness of shape, somewhat better than Takachiho’s, with a liquor colour a shade lighter than Takachiho’s, good aroma, and a mild, favourable astringency — internal quality judged comparable to Takachiho’s, external appearance slightly ahead of it. Chemically, total nitrogen in first-flush leaf sits at about the same level as Takachiho and Yabukita, but tannin content runs roughly one percentage point higher than Yabukita’s and about one point lower than Takachiho’s, putting its tannin-to-nitrogen ratio at 2.45 against Takachiho’s 2.58 and Yabukita’s 2.09. Commercially, Unkai is not confined to kamairicha alone: it is sold as ordinary sencha and deep-steamed (fukamushi) sencha as well as pan-fired tea and black tea, though its registered purpose and its best-documented quality results are both specifically for the pan-fired style, and its cultivation today remains concentrated in Miyazaki’s Kyushu kamairicha districts.