Canh chua is a soup from Vietnam that can be made in a variety of ways, though it essentially consists of seafood and vegetables in a sweet and sour broth. The broth is flavored with tamarind to give a sour tang and then balanced with fruits such as pineapple for sweetness. Herbs and chilies are added to give a hot and spicy taste and some complexity. The type of seafood used can be nearly anything available, but it often is catfish or bass. The vegetables included in canh chua usually include okra to help thicken the sauce, a type of Vietnamese celery, bean sprouts and tomatoes that are cooked with the fish until all of the flavors have melded together.
Fish or seafood is one of the main ingredients in canh chua, and it can help to define what else is added to the soup. Catfish — including the heads, tails and sometimes even the entrails — is used most often. Other types of fish include sea bass, salmon and tuna. The dish also can be made with eel, prawns, beef or no fish at all, although fish sauce would be used in its place, if available.
The sauce for canh chua is centered on the use of tamarind. This is a very sour-tasting ingredient that can be used fresh but is more often found as a paste or a concentrated liquid that is sometimes sweetened. Other ingredients that are common to the soup are rice paddy herb — called ngo om — that has a very aromatic cumin flavor, and Vietnamese coriander, which is called rau ram. Lemongrass, pineapple, onion, garlic, ginger, sugar and celery also can be added to the soup base.
The variety and amount of vegetables in canh chua varies from one recipe to the next. Okra is frequently included, because it can help to thicken the sauce, just like the fish heads will. Tomatoes, bean sprouts, water spinach and bamboo shoots are all vegetables that can be found in different versions of canh chua. Although not every recipe calls for it, ingredients such as hot chili peppers, hot sauce, chili paste or other spicy condiments can be added to round out the flavor.
Canh chua is made in a very simple way. All of the ingredients are added to a pot along with a good amount of water. They are brought to a boil and allowed to simmer for some time. Fish sauce can be added to increase the seafood flavor, if necessary. When done, the fish can be taken out and served separately, or the whole soup can be ladled over freshly made white rice.