Southern Thai — this paste is almost entirely absent from Northern and Central Thai cooking; it defines the sour, turmeric-forward character of Southern Thai cuisine
Southern sour curry paste (phrik gaeng som) is one of the most regional and uncompromising of Thai pastes — it uses dried red chillies and fresh turmeric (not kaffir lime rind or galangal) as its defining aromatics, and contains no coconut in its corresponding curry. Fresh turmeric (kamin) is pounded raw into the paste, producing a vivid yellow-orange colour and the characteristically earthy, slightly bitter turmeric flavour that distinguishes gaeng som from all other Thai curries. Kapi content is very high, and dried shrimp may be added. The resulting paste is designed to work with sharp, sour liquid (tamarind water or green mango) rather than coconut cream.
The sourness of gaeng som is the structural element — turmeric paste + tamarind + fish is the Southern trinity that makes this arguably the most distinctly regional Thai curry style.
{"Fresh turmeric (not powder) is essential — the volatile oil content of fresh kamin is entirely different from dried","No galangal, no kaffir lime rind — the aromatic set is intentionally lean and direct","High kapi content: more kapi than any other standard Thai paste","Dried red chillies only — fresh chillies would make the paste too raw-tasting for the long-simmered curry","Shallots are charred whole before peeling and pounding — this is a Southern technique for this specific paste"}
Fresh turmeric stains intensely and permanently — wear gloves when handling and work on a surface that can be scrubbed. The staining of the mortar is considered a quality indicator in some Southern Thai kitchens — a mortar that has processed many batches of turmeric paste has absorbed aromatic compounds.
{"Adding galangal or kaffir lime rind — it produces a hybrid paste that belongs to neither curry style","Using turmeric powder — lacks the fresh camphor-earth dimension of fresh kamin","Under-adding kapi — gaeng som tastes flat and lacks its characteristic fermented backbone without a generous kapi content","Attempting to add coconut milk to the finished curry — gaeng som is explicitly a no-coconut preparation"}