Yuzu

• yuzu柚子

  Japanese

• yuja유자

  Korean

• xiāngchéng香橙

  Mandarin

  The Japanese characters for yuzu, 柚子, read in Mandarin as yòuzi, which means pomelo — a large, mild, thick-skinned citrus that is not a substitute. A Chinese label reading 柚子 is selling pomelo.

The peel is aromatic and mildly bitter rather than sour; the sourness belongs to the juice. Used as a seasoning, yuzu contributes fragrance almost entirely.

Intensely citrus and unusually complex: lemon and mandarin at the front, grapefruit and something floral and faintly pine-like behind. The aroma is far stronger than the juice would suggest.

Green or bright yellow peel, depending on the harvest; dried and ground, a pale yellow.

Fresh zest is fine and oily; dried peel is brittle and grinds to a light powder.

• Limonene — By far the largest component of the cold-pressed peel oil, and the broad citrus note yuzu shares with every other citrus. It does not by itself explain what makes yuzu smell of yuzu.(what limonene is)
• γ-Terpinene — The second-largest component, contributing a fresh, slightly herbal edge.(what γ-terpinene is)
• Linalool — Present only in trace amounts and still among the most aroma-active compounds in the oil, which is the floral note that separates yuzu from lemon. Quantity and impact are different measurements, and this is the clearest case of it in the peel.(what linalool is)

Grate or pare the peel at the last moment and put it on the food as it is served. If you have no yuzu, lemon zest with a smaller amount of mandarin or grapefruit zest comes closer than any single citrus — and loses the floral depth that makes yuzu worth seeking out.

Fresh peel on clear soups, simmered vegetables, chawanmushi and grilled fish; dried peel in shichimi togarashi and seasoning salts; pounded into yuzu kosho with chilli and salt for grilled chicken, hot pots and noodles. The juice makes ponzu with soy sauce. In Korea the whole fruit becomes yuja-cha.

• grinding — Grated fresh, the zest gives its whole aroma at once and loses it within minutes, which is why it goes on at the table.
• infusing — A strip of peel laid in a hot clear soup scents the broth in the time it takes to serve, and is eaten or left.
• boiling — Long simmering drives off the aroma and leaves bitterness. Yuzu is not a braising aromatic.

Rub a pinch of dried yuzu between the fingers. It should smell clearly of citrus; if it smells only of dust, or of turpentine, it has faded or oxidised.

• Little or no citrus smell
• A resinous, turpentine-like note
• Clumping in the jar

• Evaporation of the volatile citrus oils, fastest once cut or ground
• Oxidation of limonene and related compounds towards a flat, turpentine-like note

Rutaceae

A thorny evergreen shrub or small tree with leaves on conspicuously winged stalks, bearing small, knobbly, seedy fruit that ripen from green to yellow. The fruit has little juice and many seeds, and a thick, oil-rich, uneven rind.

Central and western China, from where it reached Korea and Japan. Japan and South Korea are now where it is grown and used in quantity.

• Japan (Shikoku and southern Honshu) — major producer. The main Japanese growing areas; the mountain villages of Shikoku are the best known.
• South Korea (Southern coast) — major producer. Grown largely for yuja-cha, the sweetened preserve.
• China — origin

Two harvests of one fruit: green yuzu in late summer, yellow from late autumn into winter. The green fruit is sharper and more herbal, and is the one pounded with green chilli into green yuzu kosho.

1. Zesting or peeling — For fresh use, the outer rind is grated or pared thinly just before serving, avoiding the pith.Why: The aroma is in oil glands in the coloured outer layer and is lost within minutes of cutting.
2. Drying — For the dried seasoning, peel is dried at low temperature and ground or cut into small pieces.Why: A shelf-stable form for seven-spice condiments and seasoning salts.

Grown as small orchard trees, commonly grafted, and slow to come into bearing from seed. Fruit is picked green in late summer for its sharper aroma and yellow in late autumn and winter for the fuller one.

Unusually cold-tolerant for a citrus, surviving frosts that would kill a lemon or orange, which is why it can be grown in upland Japan and southern Korea.

Fresh whenever you can get it, frozen whole fruit next, and dried peel for condiments and seasoning salts where it is the only practical form. The fresh aroma is the point and the dried form keeps only part of it.

• Fresh fruit heavy for its size, with a firm, fragrant, unblemished rind.
• Dried peel that smells clearly of citrus when the jar is opened.
• For bottled products, a label that says what proportion is yuzu — many "yuzu" products are mostly another citrus.

Yuzu reached Japan from China early, and by the classical period was established there as a seasonal fruit whose peel and juice marked the autumn and winter kitchen. In Korea it became the basis of yuja-cha, a sweetened preserve drunk as a tea. Outside East Asia it was barely known until the late twentieth century, when restaurant cooking took it up, and its reputation abroad now runs far ahead of its availability.

Largely domestic to Japan and Korea, with exports of fresh fruit restricted by plant-health rules in several countries. Most yuzu met abroad is juice, dried peel or a processed product rather than fruit.