The kaffir or kieffer lime tree is a Southeast Asian citrus variety which has a distinctive flavor that infuses many classic dishes from this region of the world. Thai food in particular uses a great deal of kaffir lime, and it also appears in foods from Indonesia, Cambodia, Sri Lanka, China, and Malaysia, among others. Fresh kaffir lime leaves and fruit are sometimes available in Asian markets, and the dried leaves are often readily available, especially in areas with a large Thai population. Kaffir lime can also be grown at home in USDA zones 10 and 11.
Like many citrus trees, the kaffir lime is festooned with thick, sharp spines which inspired the scientific name Citrus hystrix. The tree produces extremely knobbly roughly pear shaped fruits and distinctive hourglass shaped leaves. Kaffir lime leaves look like two leaves attached end to end, and they are dark green and very glossy, with a hint of leatheriness. The fruits are bright green to yellow and their rinds contain a great deal of flavorful oil.
The leaves are often simmered in soups and curries to lend a distinctive floral citrus flavor. The fruits may be peeled for their zest, which is often included in curry sauces such as Thai green curry, and the fruits can also be juiced. The juice of kaffir limes is not usually used in cooking, although it does appear in cosmetics and hair rinse products. Leaves, zest, and juice all have an intense citrus aroma and a distinctive sour flavor.
When fresh leaves are available, they are preferable, as they have more flavorful oils. Some markets also sell frozen leaves, when fresh leaves are not convenient. The dried leaves must be used in a higher concentration, and they should be stored in a cool, dry, dark place. If you make a lot of Southeast Asian food and you live in a subtropical area, it may be more convenient to grow a kaffir lime tree and harvest leaves and fruits as needed.
There has been some controversy over the name of the food, since “kaffir” is a derogatory term in South Africa. Some people prefer to call it makrut or magrood lime, as the connection between offensive slang and this delightful tree is somewhat unclear. It may also be called limau purut, odu dehi, shauk-nu, swangi, or jeruk purut, depending on what region of Southeast Asia one is in.