Ask any group of Thais what their favourite soup is and the answer is sure to be Tom Yam Kung (sometimes spelled Gung), piquant and delicious.

This piquant prawn soup can be found everywhere in Thailand, from the far north to the deep south, from food stalls on the streets of Bangkok to the capital's top restaurants and beyond. Its appeal to locals and visitors alike is so ubiquitous that for many people it has come to symbolize Thailand.

The soup has a unique hot and sour flavour, made tempting by the aromas of the herbs that go into the making of it - lemongrass, chili, garlic, lime juice, shallot, galangal and kaffir lime leaves. Many people regard it as a medicinal soup as the herbs that spice the soup are known to have rich medicinal values, but its popularity lies in its exquisite flavour, not its curative properties.

Garlic for instance, is known to lower cholesterol levels. Lemongrass has been proven to contain therapeutic volatile oils which act as diurectics and have antiflu and antioxidant properties. Chili has at its heart capsaicin, a chemical said to improve respiratory and blood circulation functions. Galangal, an aromatic and pungent herb contains essential oils rich in antirheumatic and antimicrobial properties.

The soup is always served topped with kaffir lime leaves, said to improve the appetite as Its distinctive flavour makes the dish more appetizing.

The local lime juice that is a popular flavouring for most Thai foods, including tom yam kung, is credited with antitussive, stomachic and anticorbutic properties. Shallots, one of the soup's basic ingredients, also relieves stomach disorders and possesses antidiarrhoeal, expectorant and diuretic properties.

The presence of these properties and their effects on the digestive system have been recorded in a Japanese study into antioxidants (1993) when it was shown that the Thais have an extremely low rate of digestive tract cancer. The study attributed this to the unique properties of galangal, lemon grass, and kaffir lime leaves.

Recipe for Tom Yam King Soup

Ingredients

7-8 prawns

350 g. mushrooms

1 lemon grass stem

7-8 kaffir lime leaves

2 sprigs cilantro (if available)

5 fresh chillies

3 Tbsp fish sauce or thin soy sauce

2 Tbsp roasted chilli paste

4 Tbsp lime juice

5 cups chicken broth

Peel and quarter mushrooms, then shell, clean, and devein the prawns. Wash lemongrass, karrif lime leaves, cilantro (if using) and chillies. Slice lemon grass stem, tear kaffir lime leaves (remove centre spine), pound chillies and slice in half and chop cilantro. Pour chicken broth into pot and bring to boil slowly, then add kaffir lime leaves and lemon grass and boil for 5 minutes. Add mushrooms and prawns, bring to boil for about 3 minutes, then turn off the heat. Season to taste with lime juice, fish sauce or soy sauce, roasted chili paste and pounded chillies, add chopped chilantro and place in bowls immediately and serve. Delicious!