Kabosu

What it is

The fruit is almost round, with a slightly pebbled rind and about 17 seeds on average. In Riverside, California, fruit averages about 5.3 cm (2.1 in) across. A green outside hides yellow flesh, ranging from pale to deep yellow. Kabosu’s main kitchen role is as a sour seasoning; its juice also goes into vinegar and marmalade.

Where it comes from

Ōita is kabosu’s centre in Japan: it grew 99% of the Japanese crop in 2018. Usuki, Taketa, Bungo Ōno and Bungo Takada are its main growing areas. An Usuki legend tells of Sogen, a doctor who brought a sapling from Kyoto during the Edo period.

The regional name Ōita kabosu gained geographical-indication protection in 2017, tying that name to fruit from its growing region.

How it's eaten where it grows

In Ōita, a squeeze of kabosu seasons shiitake mushroom tempura, mozuku seaweed, miso soup and fried chicken. The juice also makes ponzu, a sour soy sauce: equal parts kabosu juice and soy sauce, with smaller amounts of sake and mirin, steeped with kombu seaweed.

The fruit works beyond a fresh wedge. Juice frozen in an ice tray gives small portions for later cooking, and marmalade carries the citrus into a sweet preserve.

How it's grown

Kabosu trees spread into a dense crown, with short thorns on some branches. At Riverside, trees grafted onto Carrizo or C-35 roots stand about 3 m (10 ft) tall at 20 years old. In Usuki, grower Teruyuki Fujiwara removes leaves and small branches around the fruit to let sunlight reach the rind and deepen its green colour.

When and where you'll find it

Ōita’s outdoor season usually runs from August to October. Stored fruit follows from October to March, with greenhouse fruit from March to July. In Riverside, California, the usual season is September and October.

Bottled juice travels too: Kabosu Honke juice from Japan comes in 1.8-litre (61 fl oz) bottles, for marinating chicken, beef or fish and for cocktails.