The Thai mortar salad is a technique where the mortar is the mixing bowl and the pestle bruises ingredients to release juices which become the dressing. This is not chopping and tossing in a bowl — the controlled bruising creates the characteristic texture and integrated dressing of som tam.
Built in stages: garlic and chillies pounded into rough paste first. Palm sugar and fish sauce next. Lime juice follows. Then the shredded papaya gets bruised — not pulverised — with gentle pounding and tossing. The bruising breaks cell walls on the surface, releasing juice that mixes with the dressing base. The texture is the point: lightly bruised but still crunchy.
The large clay mortar with wooden pestle is specific to this technique — granite is too aggressive. The motion combines gentle pounding with tossing using a spoon in the other hand. Taste after every addition. The balance should be sweet, sour, salty, and spicy all at once.
Pounding too hard — you're bruising not making paste. Adding all dressing at once instead of building layers. Not tasting as you go. Using a small granite mortar — this needs a large clay mortar. Shredding papaya too fine. Forgetting peanuts and dried shrimp go in last with only a light tap.