Citrus junos Seeds | Yuzu
LATIN NAME: Citrus junos
COMMON NAME: Yuzu, Japanese Yuzu
Plant Profile
The flowers open white and heavy-scented in spring, borne in the leaf axils, and the fruit hangs for most of the year. Yuzu ripens from late autumn into midwinter, and the fruit is a knobbly oblate globe of 7 to 10 cm with a thick rind and a great many seeds. The juice is sharply acid, high in citric acid with a good measure of ascorbic acid, so the flesh is a by-product of the peel.
Because that thiol sits at the front of the aroma, yuzu peel oil is prized in flavour work at doses so small that a change of a few parts per million is detectable. Nootkatone, the oxygenated sesquiterpene familiar from grapefruit, appears in yuzu as well, adding a bitter-citrus depth under the bright top notes.
Nobody eats a yuzu out of hand. The juice goes into dressings and dipping sauces, where a spoonful cuts through soy and sesame, and the zest is grated over fish and grilled vegetables. The rind is also salted with chilli and left to ferment into a pungent paste used in soups and hotpots in pinches rather than spoonfuls.
The thick, pitted rind is high in pectin, so a yuzu marmalade sets without added gelling agent and holds its perfume after boiling. Slice the fruit thinly, soak it, then simmer it with sugar and a little of the juice. Seville orange makes a darker, more austere marmalade; yuzu makes a brighter one. The two are worth keeping side by side.
Indoors, the citrus leaf miner draws silver galleries through young foliage while soft scale and cottony cushion scale colonise the leaf undersides and drip honeydew. Wash the foliage monthly, remove badly mined shoots, and pick scale off by hand. Prune in late winter, cutting out crossing branches to open the crown; gloves are advisable, since the thorns are long.
Science & Biotechnology
Cold pressing of fresh peel gives the oil most faithful to the fruit, and the food trade prefers it; steam distillation gives a cleaner fraction and scales easily from the peel left after juicing. Supercritical carbon dioxide extraction has been studied for yuzu because it avoids the heat that rearranges the thiol, and the spent peel still carries hesperidin and pectin.
Uses & Benefits
Press the rind and the oil ducts in the flavedo release limonene with a strong contribution from gamma-terpinene, myrcene and p-cymene. What separates yuzu from every other citrus peel is its top note: a sulfur-containing thiol, 8-mercapto-p-menthan-3-one, present at vanishingly low concentration and responsible for the grapefruit-and-flowers character that survives cooking.
Whole fruits go into the midwinter bath in Japan, a custom in which the floating fruit perfumes the water and the peel is tied in cloth so the pips do not escape. In the kitchen the fruit is halved into hot drinks with honey or preserved in sugar syrup, and the peel is candied for sweets. Sourness makes the juice useful without vinegar.
Growing from Seed
Genomic work has settled the parentage: yuzu is a natural hybrid between a mandarin and a cold-hardy Chinese citrus, and that second parent is where its frost tolerance comes from. The tree stays small, usually under four metres, with a dense frame of thorny branches and glossy dark leaves whose petioles carry only a narrow wing. Growers in mild regions use the thorns deliberately, planting yuzu as a boundary hedge.
An established yuzu crops outdoors in gardens that lose lemons to frost, provided the ground drains and the tree is sheltered from cold wind. Young plants and flowering wood are much more tender than the mature frame, so the first seasons decide whether a garden can carry the species. Cold air pooling in a hollow is more dangerous than a low reading on an open slope.
Yuzu is polyembryonic: several embryos form in the seed from nucellar tissue without fertilisation, so a seedling is very often a clone of the mother tree and comes reasonably true. That makes raising it from seed worthwhile, even though a grafted plant crops sooner. Sow fresh seed just covered in a gritty mix and keep it warm and barely damp.
Use two parts composted bark, one part coarse perlite and one part horticultural grit, aiming for pH 5.5 to 6.5. Water with rain water where the tap supply is hard, let the top of the compost dry between waterings, and never stand the pot in a saucer, because Phytophthora root rot is the commonest way to lose a container citrus. Move the plant on when it has four to six true leaves and a stem about pencil thickness.
Our Take
Yuzu rewards patience more than any citrus I have grown in a container: the tree sulks for a season or two and then crops heavily once the roots have filled the pot. Keep one against a sunny wall, and the winter peel is worth the wait. If the aromatic rind family appeals, the citron carries the thickest peel of all, the bitter orange gives the classic marmalade base, and the small kumquat will fruit on a windowsill.
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