The Lao/Isaan version of green papaya salad (Entry TH-08) — identical in construction but replacing standard fish sauce (nam pla) with fermented fish sauce (pla raa or padaek): a liquid extracted from fermented freshwater fish, darker, more intensely pungent, and more complex than standard fish sauce. Som tam pla raa is the preparation that divides non-Isaan palates from native ones more than any other: its fermented fish sauce provides a level of umami-fermented depth that standard fish sauce approaches but does not reach. Thompson covers it in Thai Street Food as the original form — the Bangkok version with regular fish sauce being the adaptation for less fermented-accustomed palates.
**Pla raa (fermented freshwater fish paste/sauce):** Made from whole freshwater fish (typically snakehead or catfish) fermented with salt and roasted rice bran for 6 months to a year — producing a liquid and solid of extraordinary fermented depth. Unlike nam pla (made from anchovies), pla raa has a thicker, more viscous texture and a more complex, less sharp fermented character. **Usage:** In som tam pla raa: 1–2 teaspoons of the liquid portion of pla raa replaces or supplements the standard fish sauce. The substitution fundamentally changes the flavour register of the salad from bright-salty to deep-fermented-complex. **The construction:** Identical to Entry TH-08 (clay mortar, bruising technique, four-flavour balance) with the pla raa substitution in the dressing. Decisive moment: The pla raa quantity — it is intensely flavoured and must be added in smaller increments than fish sauce, with tasting after each addition. The salad should taste of the fermented fish's depth as a background note that amplifies the other flavours, not as a dominant fermented foreground.
David Thompson, *Thai Food* (2002); *Thai Street Food* (2010)