Thai Amaranth Soup with Coconut and Lime

Thai amaranth soup is a Thai-inspired bowl of tender amaranth leaves, tofu, and mushrooms in a coconut broth brightened with lime and fragrant with red curry paste. It is warming but not heavy, and the greens cook quickly; use leafy amaranth here, not amaranth grain.

Ingredients

2 tablespoons neutral oil (30 ml), such as canola or avocado oil
3 tablespoons Thai red curry paste (45 g); check the label if you need a vegetarian or vegan paste, since some contain shrimp paste
1 stalk lemongrass (about 25 g), outer leaves removed, lower portion bruised and cut into two pieces
4 makrut lime leaves (about 1 g), torn, optional
1 tablespoon finely grated fresh ginger (6 g)
1 medium yellow onion (about 150 g), thinly sliced
4 cups low-sodium vegetable broth (950 ml)
1 can unsweetened coconut milk, 13.5 ounces (400 ml); shake or stir it before measuring
2 cups sliced cremini or other mild mushrooms (150 g)
1 package firm tofu, 14 ounces (400 g), drained and cut into ¾-inch (2 cm) cubes
8 cups loosely packed amaranth leaves (about 200 g), washed, drained, and roughly chopped; thin tender stems may be included
1 tablespoon soy sauce (15 ml)
1 teaspoon packed brown sugar (4 g)
1 to 2 tablespoons fresh lime juice (15 to 30 ml), to taste
¼ teaspoon fine salt (about 1.5 g), plus more to taste
1 small red or green Thai bird’s-eye chili (about 5 g), thinly sliced, optional

Instructions

Prepare the greens and aromatics. Rinse the amaranth leaves well, especially around the stems, and drain them thoroughly. Roughly chop the leaves and any thin, tender stems; discard thick or woody stems. Slice the onion, grate the ginger, and cut the tofu into cubes. Bruise the lemongrass by pressing it firmly with the side of a knife so it releases its aroma. These tasks take about 20 minutes, depending on how much trimming the greens need.
Fry the curry paste. Set a medium-large pot over medium heat and add the oil. Stir in the curry paste and cook for 2 minutes, stirring often, until fragrant. Keep the heat moderate: curry paste can scorch quickly, and a burned paste will make the broth taste bitter. If it sticks before it becomes fragrant, add a teaspoon of broth rather than turning the heat high.
Soften the onion and aromatics. Add the onion, ginger, lemongrass, and torn makrut lime leaves, if using. Cook for 3 minutes, stirring, until the onion begins to soften and the aromatics smell fresh and citrusy. The lemongrass pieces are there to perfume the broth, not to eat; leave them large enough to spot and remove later.
Build the coconut broth. Pour in the vegetable broth and coconut milk, then add the soy sauce, brown sugar, and salt. Stir to loosen any curry paste from the bottom of the pot. Bring the liquid just to a gentle simmer, then simmer uncovered for 8 minutes. Avoid a hard boil, which can make the coconut milk look separated and cause more liquid to evaporate than intended.
Cook the mushrooms. Add the sliced mushrooms and simmer for 5 minutes, until tender but not falling apart. If you prefer a broth with more body, press a few mushroom slices gently against the side of the pot with a spoon; there is no need to blend the soup.
Warm the tofu and wilt the amaranth. Add the tofu and simmer for 3 minutes, then stir in the chopped amaranth and cook for another 3 minutes. The leaves should be wilted and tender while retaining their green color. If the pot looks crowded at first, add the greens in two handfuls; they shrink considerably as they soften.
Finish and taste. Turn off the heat, remove the lemongrass pieces, and stir in 1 tablespoon lime juice. Taste the broth. Add more lime for brightness, soy sauce for savory depth, salt if it tastes flat, or the sliced chili for heat. Serve while hot. The full cooking sequence takes about 25 minutes.

Tips

Choose leafy amaranth. Amaranth is sold as both a leafy vegetable and a grain. This recipe uses the leaves, sometimes labeled amaranth greens or Chinese spinach at Asian markets. If you cannot find them, use the same weight of baby spinach for a milder, softer soup, or mature spinach for a closer leafy texture. Add spinach near the end, just as you would the amaranth.
Adjust the curry paste gradually. Brands vary in saltiness and heat, and some include shrimp paste. Start with 2 tablespoons if you are sensitive to spice, then add more after tasting the broth. For a vegetarian soup, choose a paste without shrimp and keep the soy sauce; for a gluten-free bowl, use gluten-free tamari and check the curry paste label.
Keep the coconut broth gentle. A lively simmer is enough. Boiling hard can cause the coconut milk to separate and may break up the tofu. If it does separate slightly, stir gently; it will still taste good, though the broth may look less smooth.
Balance the finish in small additions. Lime, salt, and chili are easiest to adjust at the end. Add lime a teaspoon at a time if yours is especially sharp, and taste before adding extra salt because curry paste and soy sauce already season the soup.

Serving Suggestions

Serve the soup in deep bowls as a light meal, or ladle it over steamed jasmine rice for a more filling dinner. Rice noodles also work: cook them separately according to their package directions and divide them among bowls before pouring the soup over them. Keeping noodles separate prevents them from soaking up too much broth if you expect leftovers.

Offer lime wedges, sliced chili, and chopped cilantro at the table so each person can adjust the brightness and heat. A small dish of sliced cucumber or a crisp salad with a simple lime dressing makes a refreshing side. If serving several people, remove the lemongrass before bringing the pot to the table, and remind everyone that any remaining pieces are aromatic flavoring rather than tender vegetables.

Variations

Use a different green: Young spinach, chard, or water spinach can stand in for amaranth. Chop chard stems finely and add them with the onion so they have time to soften; add the leaves near the end. Water spinach has hollow, tender stems, so slice them into short lengths and cook them with the leaves.

Make it more substantial: Add 1 cup (150 g) cooked chickpeas with the tofu, or serve the soup with rice. For a seafood variation, omit the tofu and add peeled raw shrimp near the end, simmering until opaque and cooked through; check the thickest pieces with a food thermometer and cook seafood to the USDA FSIS safe minimum of 145°F (63°C). Do not add cooked seafood early, as it can become tough.

Change the aromatics: Lemongrass and makrut lime leaves can be difficult to find. If lemongrass is unavailable, omit it and add an extra teaspoon of lime zest at the end; the soup will lose some of its grassy citrus aroma but remain bright. If you cannot find makrut lime leaves, omit them rather than substituting ordinary lime leaves, which are not the same ingredient.

Make it less rich or hotter: For a lighter broth, replace up to half the coconut milk with additional vegetable broth. It will be less creamy and have a milder coconut flavor. For more heat, add sliced bird’s-eye chili at the table or stir a little extra curry paste into a ladle of hot broth before returning it to the pot.

Storage and Reheating

Refrigerate leftovers within 2 hours of cooking in a covered, shallow container. The soup keeps for 3 to 4 days in the refrigerator. The greens will soften and darken a little as they sit, but the broth remains suitable for reheating. If you know you will have leftovers, keep rice or noodles in a separate container so they do not absorb the soup.

Reheat only the portion you plan to serve in a saucepan over medium-low heat, stirring gently until steaming throughout. Avoid a rolling boil, which can separate the coconut milk. For food safety, leftovers should reach 165°F (74°C); check the center with a food thermometer. You can also microwave a serving in a covered microwave-safe bowl, stirring halfway through and checking the temperature in more than one spot.

To freeze, cool the soup promptly and transfer it to freezer-safe containers, leaving a little room for expansion. Freeze for up to 2 months for best quality. Thaw overnight in the refrigerator and reheat as above; the coconut broth may look slightly separated after freezing, so stir gently as it warms. The tofu and greens will be softer than when freshly cooked.

Frequently Asked Questions

Can I use amaranth grain instead of amaranth leaves?
No. This recipe is written for leafy amaranth, which wilts into the soup in a few minutes. Amaranth grain needs a different amount of liquid and a much longer cooking time, so it cannot be swapped in directly. If you want to use the grain, cook it separately according to its package directions and add a spoonful to each bowl.

Is this soup traditionally Thai?
This is a Thai-inspired home-style soup, not a claim to one definitive traditional recipe. Thai ingredients such as curry paste, lemongrass, coconut milk, and lime guide its flavor, while the choice of greens and other additions can vary. Thai households and regional cooking traditions are diverse, and recipes are not all identical.

Can I make it ahead?
Yes. You can wash and chop the greens, slice the onion and mushrooms, and cube the tofu up to a day ahead; keep them covered in the refrigerator. You can also cook the broth through the mushroom step, cool and refrigerate it, then bring it back to a simmer and add the tofu and greens just before serving. Add lime after reheating for a fresher taste.

What can I use instead of tofu?
Leave it out for a lighter soup, or add cooked chickpeas for a plant-based alternative. If using cooked chicken, add it only to warm through, and make sure previously cooked leftovers are reheated to 165°F (74°C). For raw poultry, cook it separately to the USDA FSIS safe minimum internal temperature of 165°F (74°C) before adding it to the soup.

Why does my soup taste flat?
First add a little lime juice, then taste again. Coconut milk and greens can soften sharp flavors, so the broth may need more acid or salt than expected. If it is still bland, add soy sauce a teaspoon at a time. If it tastes too sour, balance it with a small pinch of brown sugar rather than adding a large amount of salt.

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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes

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