Yuzu zest

Yuzu zest is the thin outer rind of Citrus junos, a knobbly yellow-green winter citrus believed to be an ancient natural hybrid of the wild Ichang papeda and a sour mandarin. The fruit is roughly the size of a tangerine, with a deeply pitted, bumpy skin and pale, intensely seeded flesh that is too sour and too pip-heavy to serve as a dessert fruit — culinary use is almost entirely confined to the zest and the juice. The aromatic profile of the peel is unusual among citrus: limonene and gamma-terpinene dominate as expected, but yuzu is marked out by an unusually high proportion of linalool together with yuzunone, thymol methyl ether and traces of beta-phellandrene, which together give the flavour a floral, almost violet lift on top of its grapefruit-and-mandarin core. Japanese cooks grate a few curls of zest onto clear dashi soups, fold it into saikyo miso and yuzu kosho paste, scatter it over simmered daikon, and rest a slice on the rim of a ponzu dipping bowl. On the winter solstice the whole fruit is floated by the dozen in hot tōji baths for warmth and good health. French chefs discovered the ingredient in the early 2000s — Anne-Sophie Pic, Michel Bras and Joan Roca were among the first to put yuzu on European tasting menus — and it has since become a fixture of pastry and fine-dining kitchens worldwide.