Phiw Makrut (Makrut Lime Rind)

Phiw makrut is the zest of the makrut lime, Citrus hystrix, a tree native to tropical Asia and long grown in Thai gardens, where it stands beside the kitchen as a matter of course. It belongs to the central Thai tradition of curry pastes, in which David Thompson in Thai Food treats the grated rind as a standard aromatic of the mortar, set among the rhizomes, lemongrass and coriander root. The cooks who carry it are the household and palace cooks of the central plains, for whom the rind, not the juice, is the prized part of the fruit.

The rind is the thin, intensely aromatic outer skin of the fruit of Citrus hystrix, dark green, deeply pitted and bumpy, with a fragrance of resinous citrus oil far sharper than that of any other lime. Only the green zest is used, pared or grated fine and free of the white pith beneath, which is bitter. The fruit yields little juice and is grown for its skin, and the same tree gives the double leaf, bai makrut, a separate ingredient. The rind is pounded into curry pastes such as phrik kaeng khiao waan, green curry paste, and into fish cakes, where it perfumes the paste without lending sourness.

The rind is eaten in curries of coconut milk, in fish cakes called thot man pla, and in pastes served with rice, and it is drunk beside nothing in particular, the meal taking water or a light beer. Its sharp resinous oils cut through the fat of coconut cream and the richness of fish and pork, and its bitterness steadies the sweetness of palm sugar. The structure of the Thai table is balance, and the rind supplies fragrance without adding sourness to a dish already tuned.