Som tum (ส้มตำ — literally sour pounded) originates in the northeast Thai and Lao culinary traditions. Thompson's *Thai Food* places it in the context of Isan (northeast) Thai cooking — the most chilli-forward regional tradition in Thailand, where the heat level is significantly higher than the Bangkok central standard.
A salad of shredded green (unripe) papaya pounded briefly in a mortar with dried shrimp, fish sauce, lime juice, palm sugar, chillies, and garlic — one of the most perfectly balanced dishes in any cuisine, achieving all four tastes in a single bite of extraordinary freshness and complexity. Som tum is simultaneously Thailand's most eaten street food and the dish that most comprehensively demonstrates the four-taste principle.
Som tum's simultaneous four-taste impact is explained by the mortar technique: the bruising of the papaya cells releases the fruit's natural sugars and tannins simultaneously with the chilli heat and the fish sauce's salt and umami — all four elements enter the tasting experience at the same moment because they are all present on the surface of the same bruised cell. As Segnit notes, lime and fish sauce is the defining pairing of Southeast Asian cookery — both carry compounds that individually would be overwhelming (acid, umami-salt) but in combination create a balanced savouriness that is more than the sum of its parts.
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