Sudachi

What it is

About the size of a golf ball, roughly 4 cm (1.6 in) across, sudachi has a thin, leathery skin with a lightly pebbled surface. Inside are a few seeds and pale green to greenish-yellow flesh.

It's usually picked green and immature, the stage prized for flavour. Left to mature, the skin turns yellow and the flesh becomes yellower too. The juice supplies the sourness; the grated skin is sprinkled on too.

Where it comes from

Sudachi has long been grown in Tokushima, where it began as a fruit for household use. Commercial growing expanded from around 1965. Tokushima now accounts for 98% of Japan’s sudachi shipments, so this little citrus remains closely tied to one part of the country.

How it's eaten where it grows

In Tokushima, sudachi juice goes over sashimi, grilled fish and tofu, and even into miso soup. Grated peel seasons the dipping sauce for tempura or a serving of somen noodles.

Sudachi udon puts the whole fruit’s shape on display. Thin citrus rounds cover chilled noodles in a cold, diluted mentsuyu, a soy-based noodle broth. A sprig of flowering shiso finishes the bowl.

How it's grown

Sudachi grows on a slow-growing, long-lived citrus tree, usually 1.5–6 m (5–20 ft) tall. Its spreading crown has dense branches and small thorns. Growers pick the fruit while it is still green. Tokushima uses both greenhouses and open fields, extending the fresh-fruit season beyond the outdoor crop.

When and where you'll find it

In Tokushima, greenhouse fruit usually runs from March to August, open-field fruit from August to October, and refrigerated fruit from October to March. In Riverside, California, green cooking fruit is usually picked in September and October.

Outside Japan, bottled sudachi juice is the easier form to meet: several online retailers sell it, bringing the sour juice to the kitchen without the whole fruit.