Citrus hystrix Seeds | Kaffir Lime
LATIN NAME: Citrus hystrix
COMMON NAME: Kaffir Lime
Plant Profile
The winged petiole is broad and flat, and the blade sits on it above a narrow articulation, which is why the foliage reads as double. That constriction is the practical way to tell a papeda from an ordinary citrus at arm’s length, and it occurs in the same form in the related Ichang papeda. Oil cells are packed in the petiole as well as the blade, so both halves smell when crushed.
The leaf oil is recovered by steam distillation from fresh or partly dried leaves, and the citronellal-rich fraction is the part most valued. That aldehyde is why the oil works as an insect repellent in the way citronella does, and why soaps and candles carry it. Distillers keep the boiler temperature in check, since heat and acid drive citronellal toward isopulegol.
Oil expressed from the peel tells a different story, with limonene dominant and citronellal a secondary note, plus sabinene and beta-pinene. That is why the rind smells more like citrus and the leaf more like grass, though both come from one plant.
The juice has been used as a hair rinse and in home-made shampoo, and the rind in cleaning preparations, which follows naturally from an oil that cuts grease and discourages insects. Dried leaves hold their aroma well enough to keep in a jar, and the distilled oil is diluted before it touches skin.
In climate terms this is a tropical citrus, and in most of Europe and North America it spends its life in a pot. It grows well at a metre or two in a large container if the roots are cool and the light is strong.
Science & Biotechnology
The papedas are the odd corner of Citrus: spiny shrubs with acrid oil, hardy in some cases, and they sit near the base of the genus in most analyses. Citrus hystrix shares that corner with Citrus ichangensis, Citrus macroptera and Citrus latipes, all useful to breeders as sources of hardiness and disease resistance. The thorns that earned the species its porcupine name are long and stiff on young growth.
Uses & Benefits
Tear one leaf and the whole plant explains itself. The scent is bright and lemon-like at first, then turns sharply green and medicinal, closer to eucalyptus than to any orange, and it comes almost entirely from the leaf rather than the fruit. The leaf is also built in two parts, with a winged stalk nearly the size of the blade pinched together at the joint.
The fruit is a small, dark green, deeply wrinkled ball whose peel is so bumpy that it looks diseased; there are typically half a dozen segments with a thick white pith and very little juice. That juice is intensely sour and slightly bitter, and cooks in Southeast Asia use the peel and the pith as often as the juice itself.
A leaf oil distilled from this species is built around citronellal, an aldehyde with the fresh rose-lemon character that makes citronella grass famous, and it is usually the largest single component of the leaf. With it come citronellol, citronellyl acetate, linalool, limonene and sabinene, plus a little isopulegol formed when citronellal cyclises. The composition shifts with harvest season and leaf age.
Cooks in Thailand, Cambodia and Indonesia treat the leaf, the rind and the juice as three ingredients with three jobs. The leaf goes in whole to perfume a broth, or finely shredded to be eaten; the rind is pounded into curry pastes for its bitter edge; the juice goes in at the very end.
Growing from Seed
Use a free-draining citrus mix — two parts loam, one part compost and one part grit — in a pot with a generous drainage hole, standing on feet. Keep the compost slightly acidic, and avoid potting into a container much larger than the root ball, since wet cold compost around fresh roots is the quickest way to lose a citrus.
Water with rainwater when the top centimetre dries, and feed a citrus fertiliser through the growing season, stopping in the short days of winter. Scale insects, spider mites and citrus leaf miner all build up faster in dry, still air indoors. Winter the plant at ten to fifteen degrees in the brightest place available.
Our Take
I keep a kaffir lime for the leaves alone, because one tree supplies more leaf than a household can use and the fruit is a bonus. Grow it from fresh seed if you can, and be patient with the slow start. For the same citrus kitchen in smaller form, Key lime and calamansi are easy pot subjects, while the big-fruited citron is grown for its candied peel rather than its juice.
Related Reading
More species in the same orbit as Kaffir Lime: