Lemongrass soup, also known as Tom Yum, is a popular dish in both traditional Thai and Laotian cuisine. It features hot and sour flavors brought about by a liberal use of lemongrass as well as other herbs and spices. The soup is normally a seafood soup made from a base of Tom Yum paste. Due to the combination of ingredients, many believe that lemongrass soup strengthens the immune system and helps fight cold and flu.
Prawns, shrimp, or other mixed seafood is traditionally used to prepare this dish. The seafood is cooked in a broth flavored by lemongrass, garlic, galangal, chiles, and other spices, depending on the chef's personal taste. Mushrooms are a common substitution for seafood and provide a vegetarian adaptation. Chicken can also be used instead of seafood. A spicy chile paste is sometimes added and is said to provide a nice complement to the herbal sourness provided by the other ingredients.
The dish is known by the same name in both Laos and Thailand, but there are small differences between the two versions of the soup. In Laos, a small amount of rice is added to the soup. Another variation is the addition of coconut milk to the broth.
Lemongrass soup is now popular in nearly all countries in Southeast Asia, and Tom Yum paste has been exported worldwide. The paste is made by frying the pulverized ingredients together in oil and jarring or canning the end product. Instead of using the paste, recipes online and in cookbooks encourage home cooks to try their hand at making the dish from scratch.
Not all of the traditional ingredients for this soup can be found in all local grocery stores around the world. In a pinch, the leaves of kaffir limes may be replaced by a small amount of lime juice, and galangal is often replaced by ginger. While a common substitution, replacing galangal with ginger is not the best idea because while they resemble each other, the tastes are quite different.
Many Thai and Laotian restaurants in a variety of countries serve this dish. Lemongrass soup may be served as an appetizer or in larger portions as the main course. Many feel the best type of this soup is made from scratch with fresh ingredients and either shrimp or prawns. Restaurant staff can provide assistance in deciding the proper amount of spiciness to complete the flavor profile.