Tom kha gai, literally “boiled galangal chicken,” is a popular Thai soup known for its intense galangal flavor and rich creamy coconut-infused broth. Galangal is a fibrous rhizome with a reddish-brown or pink color, related to ginger but with a different flavor. It has been described as “pungent,” “peppery,” and “floral.” Other standard ingredients in tom kha gai are lemongrass, garlic, chili peppers, kaffir lime leaves, mushrooms and fish sauce.
The essential ingredients for the flavor of tom kha gai are the coconut milk and galangal. Most commonly the soup is made with chicken, but many recipes offer the alternative of using fish or prawns in place of all or part of the chicken. Suggestions for vegetarian versions are also common, with tofu or mixed mushrooms taking the place of the chicken.
Making tom kha gai is straightforward. Chicken broth and lemon grass, kaffir lime leaves, and a touch of palm sugar are brought to a boil. Peeled galangal and birds-eye chilis, cut into thick slices, cook along with the other flavoring ingredients. The galangal and chilis are cut into chunky pieces because they are not intended to be eaten, just to add their flavor to the soup, and their large size makes them easy to avoid.
Canned coconut milk and fish sauce are added once the soup has reached a boil. For a richer flavor, all or part of the coconut milk can be replaced by canned coconut cream. The liquid from fresh coconuts, called coconut juice, can also be used in place of part of the coconut milk — giving the tom kha gai an intense fresh coconut flavor — but it does not thicken the soup, so coconut milk or cream is still needed.
Cubed, diced or shredded boneless chicken cooks in the flavored broth, absorbing the galangal flavor. The mushrooms are added with the chicken. If mushrooms take the place of the chicken, the soup becomes tom kha hed, "boiled galangal mushrooms." For vegetarian versions, vegetable broth and soy sauce take the place of chicken broth and fish sauce.
Additional flavor elements are often included, such as onions or shallots, garlic, cilantro root or leaves, diced tomato, and roasted chili paste. In Laos, and the parts of Thailand bordering Laos, dill is commonly used. Sometimes the soup is served garnished with cilantro leaves, diced tomato or other colorful items. Tom kha gai is usually served with rice as a meal, or by itself as a snack.