Makrut lime

What it is

The fruit measures about 5–7 cm (2–2.8 in) across, with deep wrinkles and bumps in its green rind. It turns yellow before falling from the tree. Inside is relatively little juice, sharply sour and a little bitter. The green outer peel supplies the aromatic zest used in curry paste.

Where it comes from

Makrut lime is grown throughout Southeast Asia. A fruit grown on Ambon, in Indonesia, was drawn for the naturalist Rumphius. Its travels also took it across the Indian Ocean: fruit from Mauritius, where it was grown, led to a plant at the botanical garden in Montpellier, France, in 1808. By 1816, a nursery near Tarascon was growing it for sale.

How it's eaten where it grows

In Thailand, the zest is pounded into panang curry paste with lemongrass, galangal and coriander roots. Roasted peanuts give that paste its nutty character. The leaves have another familiar role in tom yum soup.

Gaeng tae po gives the fruit itself a larger part. This sweet-and-sour curry combines pork belly, water spinach and coconut milk with a makrut-lime half. The fruit infuses the sauce as the curry rests, then comes out before serving.

How it's grown

Makrut grows as a small, spreading evergreen tree or shrub, reaching about 4 m (13 ft). Its leaves are glossy green and its white flowers are fragrant. Flowers can appear throughout the year. In Britain, it is grown under glass in a greenhouse or conservatory, then moved outside for summer.

When and where you'll find it

In the US, Pearson Ranch lists whole green makrut limes by the pound, about 9–12 fruit, from a neighbouring specialty citrus grower; they usually become available in late July. At Riverside, California, the fruit reaches full maturity in late winter to early spring, when the rind turns yellow and the fruit falls from the tree.