Pandan

The compound behind the smell is 2-acetyl-1-pyrroline, abbreviated 2AP, and it is one of the most potent aroma molecules in food chemistry. The human nose detects it at concentrations measured in parts per billion, which explains how one leaf scents a litre of coconut milk.

The same molecule is what makes fresh bread crust, cooked jasmine rice and pandan smell faintly like one another.

2AP is volatile and heat-sensitive in both directions: gentle heat drives it out of the leaf and into the food, while prolonged boiling drives it out of the pot altogether. This is the chemical reason pandan is added toward the end of long cooking and removed before serving.

Pandan leaves are also used in folk practice across the region as a mild infusion, and they appear in preliminary laboratory work on blood sugar and antioxidant activity. That research is early and mostly not conducted in people, so it belongs in the category of interesting rather than established.

Pandanus amaryllifolius is the one species in a large genus that carries the scent, and it is unusual among cultivated plants in that it almost never flowers. It is propagated from cuttings, which means the pandan grown in Bangkok, Kuala Lumpur and Colombo is effectively the same plant, passed hand to hand through gardens for centuries.

A plant that does not set seed has no wild population to return to, so pandan exists more or less entirely because people kept planting it.

In Malay and Indonesian kitchens it belongs to daily cooking, knotted into the coconut rice of nasi lemak and cooked into kaya, the coconut and egg jam eaten on toast at breakfast. In Thailand it wraps chicken for frying and colours desserts. In Sri Lanka, where it is rampe, it goes into curries and rice as a savoury aromatic alongside curry leaves and lemongrass.

The bright green pandan chiffon cake that shows up in Singaporean and Indonesian bakeries is a twentieth century invention, European sponge technique married to a local aromatic.

Pandan runs through both halves of Southeast Asian cooking. On the savoury side it goes into rice, most famously the coconut rice of nasi lemak, and into curries and braises in Sri Lanka and southern Thailand. Thai cooks wrap marinated chicken in the leaves and deep fry the parcels, where the leaf is a container and a perfume rather than food.

Drop one knotted leaf into the rice cooker with plain jasmine rice and the whole pot smells like a bakery.

On the sweet side it is the dominant flavour of the region: kaya jam, coconut puddings, chè in Vietnam, pandan chiffon cake, and the green layer in a hundred steamed sweets. It has a natural affinity with coconut, palm sugar and glutinous rice, and it works alongside lemongrass and ginger without fighting them.

Pandan juice, made by blending leaves with water and straining, gives both colour and flavour where a whole leaf would be impractical.

A whole leaf releases almost nothing. Bruise it first: run the back of a knife along the blade, or tie it into a loose knot, which does the same job and keeps it easy to fish out later.

For rice, add one or two knotted leaves to the pot at the start and remove them before serving. For coconut milk based sweets, simmer the leaf in the milk for ten minutes, then lift it out.

For pandan juice, blend ten leaves with 100ml of water and strain through a fine sieve. Let it stand and the deep green sediment settles out; that concentrated layer is what bakers use for colour.

Fresh leaves keep about a week in the fridge wrapped in a damp cloth. Frozen, they keep for months and lose surprisingly little, which makes the freezer aisle a better bet than the extract shelf.