1. Roast chilies, kaffir limeleaves, shallots, galangal and lemon grass and then grind them until smooth to Tom Yum paste.
2. Stir-fry the Tom Yum paste with oil. Add sliced lemon grass and kaffir lime leaves, set aside.
3. Put citric acid, salt, sugar and water into a pot. Melt it and bring to boil. Then add fish sauce and bring to boil again.
4. Add the Tom Yum paste into the pot. Stir it thoroughly and bring to boil again. Pack in plastic bags, 90 gram per bag.