Som tam is the Thai name for a sour and spicy salad most frequently made with thin slices of green papaya. Som tam comes in a variety of different styles using different ingredients although they all conform to the same rule that they contain all the four different tastes in Thai cooking: spicy, sour, sweet, and salty.
About Som Tam
The origin of the som tam most likely is in Laos, where the dish is called tam som. Some believe believe the dish came into existence in the 18th Century. The reason for this is that papaya is not native to Asia, it comes from South America like other major staples of South Eastern Asian cuisine such as chilli, corn, tomatoes, and potatoes. More likely tam som, and thereafter som tam, originated in the 15th Century in Laos as international trade in products from the Americas had already extended deep into Asia with chilli and tomato by that time established as staple of Asian cooking

The movement of people from Laos into Thailand gained pace in the 1950s with workers seeking employment in the rapidly developing city of Bangkok, and thereafter at an even greater rate when Laos became a Communist state. Lao migrants brought their food with them and the dish was gradually incorporated into Central Thai cuisine in a toned down form, although the style of som tam still commonly eaten in the north east region of Thailand is much more similar to the traditional Lao version of the dish.
Varieties of Som Tam
All varieties of som tam share the same basic defining characteristics: they encompass the four major flavours, a sliced or grated vegetable is the main ingredient of the dish, sour is the predominant flavour and the salad is prepared in pestle and mortar to release the flavours. In Thailand, however, som tam comes in two main styles: som tam Thai and som tam Lao. Som tam Thai is a sweeter dish with peanuts, lime, a little chilli and normally dried shrimp accompanying the grated green papaya. Som tam Lao is similar but less sweet, but made with fermented fish (as opposed to fish sauce as in som tam Thai). without peanuts and often with pickled paddy crabs. Foreign visitors tend to prefer the more familiar taste of som tam Thai, which is the recipe generally served in Thai restaurants in Europe and North America.
Within these two main styles of som tam in Thailand, there are wide variations in the main ingredient; not all som tom is made from green papaya. Green mango, cucumber, carrot, pork sausage, coconut and unripe banana are also commonly used. Not all som tam is raw either. A popular variation on the dish is to deep fry the raw som tam and serve it was a sticky chilli sauce and peanuts on top.
Food eaten with Som Tam
Som tam is a dish which is generally not eaten on its own, although Thai are sometimes known to eat small quantities accompanied by deep fried pork rind when consuming alcoholic drinks. Much more commonly som tam is eaten as an accompaniment to three other staples of the cuisine of the north eastern region of Thailand: sticky rice, grilled chicken (gai yang in the north eastern dialect) and larb, which is another type of salad with a high content of minced pork, flavoured with fish sauce, lime, some herbs and a lot of chilli. The combination of these ingredients is more than a sum of the parts as the sourness of the som tam cut through the fattiness of the chicken and adds flavour and moisture to the sticky rice. Som tam is strong tasting and is intended to be eaten in combination with other foods as one of several dishes which will be shared at the communal dining table.