Tom Yum or Tom Yam is a Lao and Thai clear, spicy and sour soup. Tom yum is widely served in neighbouring countries such as Cambodia, Malaysia and Singapore, and has been popularised around the world.
Literally, the words “tom yum” are derived from two Tai words: “tom” and “yam”. “Tom” refers to boiling process, while “yam” refers to a kind of Lao and Thai spicy and sour salad. Thus, “tom yum” is a Lao and Thai hot and sour soup. Indeed, tom yum is characterised by its distinct hot and sour flavours, with fragrant herbs generously used in the broth. The basic broth is made of stock and fresh ingredients such as lemongrass, kaffir lime leaves, galangal, lime juice, fish sauce, and crushed chilli peppers.
In neighbouring countries like Malaysia and Singapore, the name tom yum is used widely for various spicy soups which can differ greatly from true Lao and Thai tom yum soup. As a result, people are often confused by the disparities.
Commercial tom yum paste is made by crushing all the herb ingredients and stir frying in oil. Seasoning and other preservative ingredients are then added. The paste is bottled or packaged and sold around the world. Tom yum flavoured with the paste may have different characteristics from that made with fresh herb ingredients. The soup often includes meats such as chicken, beef, pork, or shrimp.
- Tom yum goong or tom yam kung, the version of the dish most popular among tourists, is made with prawns as the main ingredient.
- Tom yum paa (Lao) or tom yam pla (Thai) is a clear fish soup that was traditionally eaten with rice. It used to be the most widespread form of tom yam before mass-tourism came to Thailand, for fresh fish is readily available almost everywhere in the region’s rivers, canals and lakes as well as in the sea. Usually fish with firm flesh that doesn’t crumble after boiling is preferred for this type of soup.
- Tom yum gai or tom yam kai is the chicken version of the soup.
- Tom yum po taek (Lao) or tom yam thale (Thai) is a variant of the soup with mixed seafood, like prawns, squid, clams and pieces of fish.
- Tom yam nam khon (Thai: ต้มยำน้ำข้น) is a more recent variation. Almost always made with prawns as a main ingredient, a little milk or coconut milk is added to the broth as a finishing touch, and then balanced with some toasted dried chillies. This adaptation is not to be confused with Tom Kha Kai, where galangal is the dominant flavour of the coconut milk-based soup.
- Tom yam kung maphrao on nam khon, a version of prawn tom yum with the meat of a young coconut and a dash of (coconut) milk.
- Tom yam kha mu (Thai: ต้มยำขาหมู), made with pork knuckles. These require a long cooking time under low fire.
In the modern popularised versions the soup contains also mushrooms – usually straw mushrooms or oyster mushrooms. The soup is often topped with generous sprinkling of fresh chopped coriander (cilantro leaves). Sometimes Thai chilli jam (nam phrik phao, Thai: น้ำพริกเผา) is added: this gives the soup a bright orange colour and makes the chilli flavour more pronounced.
The Royal Lao version of tom yam includes a pinch of rice in the soup.
Other sour and spicy soups
Less well-known outside Thailand is tom khlong (ต้มโคล้ง), a spicy sour soup where the sourness, however, does not derive from lime juice but through the use of tamarind. Tom som (Thai: ต้มส้ม) are soups that are also very similar to tom yum but most often do not contain lemongrass or kaffir lime leaves. Depending on the type of tom som, the acidity can be derived from lime juice or from the use of tamarind.