A clear, fiery soup of pork ribs with lemongrass, galangal, kaffir lime leaves, and lime juice — the Isaan equivalent of tom yum (Entry TH-09), made in the same clear broth style but with pork rather than seafood and with the addition of ground toasted rice (as in larb and nahm tok) as a light thickener. Thom saap (saap in Isaan means 'delicious' — the name is itself a quality claim) is heavily soured with lime and sharply seasoned with fish sauce — the hot-sour register is more assertive than even tom yum. It is one of the most direct expressions of the Isaan preference for hot and sour flavours at their most unmoderated.
- Pork ribs: blanched first to remove impurities (boiled 3 minutes, drained, rinsed) then simmered in fresh water with lemongrass, galangal, kaffir lime leaves. - Simmer 45–60 minutes until the ribs are tender but not falling off the bone. - Season off heat: fish sauce, lime juice, fresh bird's eye chillies. - Toasted rice powder (khao khua — Entry TH-12): 1 teaspoon per serving, stirred in before service — it very slightly thickens and adds a nutty depth. - Generous fresh coriander and spring onion at service. The broth: clear, thin, deeply flavoured from the long pork rib simmer. The colour: faint yellow from the galangal and kaffir lime. The taste: hot and immediately sour, with the pork's depth underneath.
David Thompson, *Thai Food* (2002); *Thai Street Food* (2010)