As with most Thai dishes, the secret is in the spice base. You can have the freshest and reddest tomatoes, and you can have the richest chicken broth made by simmering free range chickens but, without the spice base, the soup will still taste flat.
To make the tastiest tom yum gai, allow enough time for the herbs and spices to impart their flavor. That means simmering them in the broth before you add the chicken and mushrooms. If you add everything at the same time, two things can happen.
First, if you simmer the ingredients just long enough to cook the chicken through, the broth will not be sufficiently flavored.
Second, if you simmer everything longer until the broth is rich and tasty, the chicken and mushrooms will be overcooked.
Do you need to brown the chicken before adding to the broth? No. You do that when cooking with chunks of meat or with bones when making broth. If using homemade chicken bone broth, that means you have already done the browning part and all the caramelized flavor are already in the broth.
You don’t need to do the same with the chicken slices. If you do, they will be overcooked by the time the soup is done.
Kaffir lime juice was used in this soup. Juice from regular limes is fine.
Before serving the tom yum gai, you may fish out and discard the galangal, lemongrass and kaffir lime leaves. They have served their purpose and you don’t need them anymore. They were retained for the photos in this recipe for illustrative purposes.
Thai hot and sour chicken soup (tom yum gai)
- 6 cups chicken broth
- 3 slices galangal - (dried is fine)
- 2 whole stalks lemongrass - tied into a knot
- 2 shallots - peeled and halved
- 2 pairs kaffir lime leaves - center ribs removed and discarded
- 2 bird's eye chilies - slit
- 4 chicken thigh fillets - cut into thin slices
- 2 cups fresh oyster mushrooms - if large, torn into smaller pieces
- 2 tomatoes - cut into wedges
- fish sauce
- lime juice
- torn cilantro
- Pour the chicken bone broth into a pot and bring to the boil.
- Drop the galangal slices, lemongrass, kaffir lime leaves and chilies into the broth. Lower the heat. Cover and simmer for 15 minutes.
- Add the chicken thigh fillet slices, oyster mushrooms and tomatoes to the broth.
- If the broth is unseasoned or underseasoned, add fish sauce at this point.
- Cover the pot once more and simmer for another 15 minutes.
- Taste the broth. Add more fish sauce, if needed.
- Drizzle in the lime juice, a tablespoonful at a time, tasting and adding as you go along until a good balance of salty and sour is achieved.
- Ladle the tom yum gai into bowls, sprinkle with cilantro and serve.