Sour Curry Paste (Kreung Gaeng Som)

Ingredients

Equipment Needed

• •Heavy granite mortar and pestle (krok hin), at least 7 inches diameter
• •Small bowl for soaking chilies
• •Spoon for scraping and folding paste

Instructions

1. 1

   Prepare the dried chilies

   Remove the stems from the dried red spur chilies and shake out the seeds. You don't need to get every last seed, but removing most of them keeps the heat controlled and the paste color clean. Soak the chilies in warm water for 15 minutes until they're pliable. Squeeze out the excess water before pounding. Waterlogged chilies make a watery paste. You want them soft, not soaked through.

   Prik haeng (dried spur chilies) are the standard for gaeng som. They're about 3-4 inches long, moderately hot, and give the paste its deep red-orange color. Don't substitute dried bird's eye chilies (prik khi nu haeng) unless you want a paste that's punishingly hot. The spur chili gives you heat and color in the right ratio.
2. 2

   Pound chilies with salt

   Add the salt to the granite mortar first, then the drained chilies. The salt acts as an abrasive, grinding against the chili flesh and breaking down the fibers. This is the hardest ingredient in the paste, so it goes in first. Pound with firm, steady strikes. Rotate the pestle as you go. You're not smashing. You're grinding. The chilies should break down into rough, fibrous strands first, then gradually become a thick, slightly chunky paste. This takes 3-4 minutes of steady pounding. Your arm will know.

   Ajarn always said: hardest first, most delicate last. Salt goes in before anything else because it's your abrasive agent. It does half the work of breaking down tough fibers. Skip the salt at the start and you'll be pounding twice as long for a worse result.
3. 3

   Add the turmeric

   Add the sliced fresh turmeric to the mortar. Pound it into the chili paste. Turmeric is fibrous, almost woody, so it needs real force. Work it until the bright yellow-orange color bleeds completely into the chili base and no white fibers remain visible. The paste should shift from dark red to a warm, vivid orange. Another 2 minutes of focused work. Your fingers will be stained yellow for the rest of the day. That's turmeric doing its job.

   Fresh turmeric (kha min) is non-negotiable here. Dried turmeric powder dissolves into nothing and gives you color without the earthy, slightly bitter bite that the fresh root provides. Find it at a Southeast Asian or Indian market. Buy extra and freeze it whole. It keeps for months and grates easily from frozen.
4. 4

   Pound in the shallots

   Add the sliced shallots to the mortar. They're softer than everything that came before, so they'll break down faster. Pound and scrape. Use a spoon to fold the mixture back toward the center after each strike. The shallots release moisture as they crush, which helps bind the paste together. You want them fully incorporated: no visible chunks, just a smooth aromatic base carrying the chili and turmeric. The paste should be getting wetter and more cohesive now. Another 3-4 minutes of pounding and scraping down the sides.

   Thai shallots (hom daeng) are small, reddish-purple, and more pungent than the large French shallots common in Western markets. If you can only find French shallots, use about 70g instead of 100g. The Thai shallot's intensity matters in a paste this minimal. Every element has to carry its weight.
5. 5

   Finish with shrimp paste

   Add the kapi last. It's the softest ingredient and the most potent. Pound it into the paste until everything is homogeneous, about 1 minute. The kapi should disappear into the mixture completely, leaving behind its deep, funky umami but no visible lumps. The finished paste should be smooth, slightly wet, vivid orange, and should hit your nose immediately: pungent shrimp, earthy turmeric, chili heat all layered together. Scrape it out of the mortar with a spoon. That's your kreung gaeng som. The kreung tam is everything. Done.

   Kapi quality matters enormously in a paste this simple. Good kapi smells pungent but clean, like fermented sea. Bad kapi smells rotten. Thai brands like Pantai or Tra Chang are reliable and widely available at Asian grocery stores. The kapi is doing the heavy lifting on umami here. Don't use a cheap one.

Chef Tips

• •This paste builds three of the most important dishes in Central Thai home cooking. Gaeng som pla (sour curry with fish and vegetables) is the classic: chunks of white fish, shredded green papaya or white radish, and tamarind broth. Gaeng som cha-om thot (sour curry with fried acacia omelet) is a Bangkok staple you'll find at every rice-and-curry shop. Gaeng som pak ruam (sour curry with mixed vegetables) is the simplest version, nothing but this paste, tamarind water, fish sauce, and whatever vegetables are fresh at the market that morning.
• •The mortar transforms; the blender merely chops. I say this constantly because people always ask. A blender shears the cell walls with a blade. A mortar crushes them with stone. When you crush shallots and chilies, the essential oils release differently, the texture is coarser and more integrated, and the paste holds together in a curry instead of dissolving into thin liquid. This isn't preference. It's physics. Krok ก่อน.
• •Gaeng som has no coconut milk. That's the whole point. It's one of the few Thai curries that relies on a clear, sour broth for its body. When you cook with this paste, dissolve it in water or stock, add tamarind pulp (makham piak) for sourness, nam pla for salt, a small pinch of palm sugar (nam tan pip) for sweet, then your protein and vegetables. The result is light, bright, and acid-forward. The anti-rich-curry. Perfect for hot weather, which in Bangkok means every day.
• •If you're making this for someone who doesn't eat shrimp, you can increase the salt slightly and add a teaspoon of fermented soybean paste (tao jiew) for umami. It's not traditional. But it follows the principle: you need a fermented element providing savory depth. Acknowledge the substitution, understand what you're replacing, and work within the system. That's principles, not recipes.

Advance Preparation

• •Kreung gaeng som stores beautifully. Pack it into a clean glass jar, press plastic wrap directly against the surface to prevent oxidation, and refrigerate for up to 2 weeks. The flavors actually deepen over the first day or two as the kapi continues to develop.
• •For longer storage, portion the paste into ice cube trays and freeze solid, then transfer the cubes to a freezer bag. Each cube is roughly enough for one serving of gaeng som. Frozen paste keeps for 3 months without losing much intensity.
• •This is a batch-cooking paste. Make a full mortar's worth even if you're only cooking for two tonight. Future you, standing at the fridge at 7pm wondering what to make for dinner, will be grateful you did the work today.

Frequently Asked Questions

Nutrition Information

1 serving (about 50g)