Kaeng som is a more substantial and spiced-up version of the region-wide sour fish or vegetable soup. Traditionally Kaeng som has stood alongside the various versions of Nam phrik as the most regular food of the Thai countryside along with rice. Both of these dishes utilise ‘wild’ leaves and fruits gathered around the village and on the edges of river banks, foods which used to be the mainstay of country people in between seasons and in times of crop failure. Nam phrik adds flavour through a dipping sauce. Kaeng som combines fish and local vegetables in a soup flavoured with the ripe fruit and sometimes the leaves of the tamarind tree, which grows everywhere in villages and around paddy fields.
With increasing prosperity, a more scientific agriculture and a huge movement of people from the country to Bangkok in recent years, Kaeng som is as likely as not nowadays to contain farmed seafood and lots of market vegetables. This version is a country one, using a mixture of freshwater fish, the water spinach that still grows wild in unpolluted waterways, and the produce of house gardens. Note, however, that the recipe may be adapted to seafood of all kinds with more exotic vegetables.