Fermented fish preparations are among the most ancient in Southeast Asian cookery — predating written culinary records and reflecting the essential preservation technique of inland communities without access to ocean fish or refrigeration. Thompson traces pla ra through the Isaan manuscript tradition as a foundational element of the cuisine, present in virtually every preparation. He notes that its smell, alarming to the uninitiated, is simply the smell of fermentation — of the same family as Roquefort, aged parmesan, and miso, producing complexity through controlled microbial action.
Two fermented fish preparations of northeastern Thailand that Thompson identifies as the foundational flavourings of the Isaan kitchen — pla ra (fermented fish sauce of greater complexity and depth than nam pla) and pla som (fermented fish with cooked rice and garlic, resulting in a sour, complex, slightly funky whole fish). Both are the result of lactic acid fermentation — the controlled breakdown of fish protein by salt and beneficial bacteria over weeks or months. Thompson describes pla ra as the flavour that makes Isaan food taste of Isaan — its presence in a preparation is unmistakable and untranslatable. It is more pungent than nam pla, more complex, with a depth that makes the same dish seasoned with pla ra rather than nam pla unrecognisably different.
Pla ra's extraordinary depth comes from the proteolysis of fish protein during fermentation — the breakdown of fish muscle protein by indigenous bacteria (primarily lactobacillus and various halotolerant species) produces free amino acids (primarily glutamic acid and aspartic acid) in concentrations far higher than unfermented fish or even nam pla. As Segnit notes, fermented fish preparations across cultures (fish sauce, garum, Worcestershire sauce, anchovy paste) all operate through the same mechanism — they are among the most concentrated sources of glutamate in the food world, which is why a tablespoon of fermented fish preparation can do what a kilogram of fresh fish cannot: make a dish taste completely, profoundly of itself.
**Pla ra:** - Made from small freshwater fish (typically mealfish or snakeskin gourami) fermented with salt and cooked rice in an anaerobic vessel for 3–6 months minimum. The result is a thick, opaque, intensely flavoured liquid with floating fish pieces. - Used in cooking: strained and used as a deeper, more complex substitute for or supplement to nam pla. Used in raw form in some nam prik preparations. - The smell: complex, pungent, savoury, fermented. It is not unpleasant when understood — it is the smell of extreme umami development through fermentation. **Pla som:** - Whole freshwater fish fermented with cooked sticky rice, salt, and garlic in a sealed vessel for 3–5 days (shorter than pla ra — a quick fermentation that sours the fish rather than breaking it down). - Result: the fish is slightly sour, the flesh slightly softened, the skin retaining its texture. - Served fried — the fermented fish fried in oil until the exterior is crisp and the interior is thoroughly heated and slightly caramelised.
*Thai Food* (2002); *Thai Street Food* (2010)