As promised in a recent article, here is another of the essential Thai flavour ingredients that define a true Thai dish: the kaffir lime leaf, or more correctly, the makrut lime leaf.

The makrut or Indonesian lime is a native of Thailand and Indonesia. The scientific name for the fruit is Citrus hystrix or alternately Citrus amblycarpa. Hystrix is from the Greek word for porcupine and refers to the thorns that cover the tree. Amblycarpa means “leprous” and refers to the unattractive wrinkly and tough rind of the fruit. There is not much juice in the fruit, and what little there is has a very bitter flavour and is not used in cooking, although it is considered a good hair tonic by the locals and is touted as preventing hair loss.

 In contrast to the lime we are accustomed to in North America, it is the leaf of the tree, and not its fruit that is prized by cooks for making Thai dishes. The zest is also used to a lesser extent, and is an important ingredient in red curry paste. Both the leaves and the zest contain a form of citronella which imparts the characteristic lemony-floral aroma and flavour. This beautiful scent is like an exotically perfumed room freshener.

My first exposure to the leaves was at a lunch I had in a tiny Thai noodle house in Vancouver. While waiting for my curried noodle dish, I discovered a display shelf of distinctively Thai ingredients, including bags of dried kaffir leaves. My friend said that she had tried some fresh ones and that I would enjoy them, so I bought a bag to take home. Once home, I tried tossing a few of the dried leaves into some rice I was cooking. I was immediately delighted by the beautiful smell, and subsequently by the flavour. I later read that dried leaves were just a hint of what could be achieved with fresh, and I have now found a source here in Calgary. It is likely that even a year ago you would have had a hard time finding fresh leaves, but they are quite readily available at any large Asian or Vietnamese grocery store. The difference between using dried and fresh lime leaves can best be compared to using dried Bay leaves versus fresh: there is no comparison.

Once you have found fresh leaves, freeze some for later. They will last for several months in the freezer. In fact, you can sometimes find them already frozen in the stores. The kaffir leaf is used like a Bay leaf: added whole during cooking and then removed before serving. The leaves should be bruised before adding to the pot to allow their full essence to get out. The leaves are also used in some dishes as an edible garnish, but should be thinly slivered before using. If a recipe calls for one fresh leaf, you can substitute with several dried. If you can=t find the leaves at all, you may substitute with regular lime zest or juice, but I guarantee that you will never be able to replace exactly the perfumy note that the kaffir leaf is recognized for.