Lemongrass

Citral: the scent molecule

Lemongrass owes its intense lemon fragrance to citral — a mixture of two isomers (geranial and neral) that is the same compound responsible for lemon peel’s scent. Lemongrass contains 65–85% citral by weight of essential oil, making it one of the most citral-concentrated plants available. The compound provides the quintessential citrus note to Southeast Asian curries and soups without any actual lemon.

The white base technique

Only the bottom 10–15 cm of the lemongrass stalk — the pale, tender section just above the root — is used in cooking. The upper green stalks are too tough and fibrous. For curry pastes and marinades, the white section is sliced extremely thin across the grain, then pounded in a mortar to release the cell content. For soups and curries where it will be strained, whole bruised stalks are used — bruised with the back of a knife to open the cells and release the aromatic compounds.

Kaffir lime, galangal, lemongrass

These three herbs define the aromatic signature of Thai and Khmer cooking. They never substitute for one another — each provides a different dimension: lemongrass gives citrus-grassy brightness; galangal gives pine-medicinal depth; kaffir lime leaves give floral-citrus intensity. Together they are the foundation of tom yum, green curry paste, and laab salad dressing.

Citronella

Citronella oil — used in insect repellent candles and sprays — is extracted from a different Cymbopogon species (C. nardus) than the culinary lemongrass (C. citratus). They are closely related but distinct plants. Culinary lemongrass does contain citral, which has minor insect-repellent properties, but it is not the same as citronella grass.