Saffron Red Lentil Soup

Red lentils collapse into purée in about twenty minutes, which makes this a weeknight soup and also makes it easy to serve something flat. A saffron lentil soup needs 25 threads (0.10 g) bloomed in warm water, properly toasted cumin, and enough lemon at the end to wake the whole pot up.

Red lentil soup belongs to Turkey, the Levant and half of South Asia, and in none of those kitchens does it contain saffron. Cumin, mint, chilli, sometimes a swirl of browned butter — that is the standard vocabulary.

So this is an addition, not a restoration, and it is worth being clear about what it is for.

Why put saffron in a lentil soup?

Split red lentils are the fastest legume in the kitchen and the least interesting. They cook to a mild, slightly sweet purée that takes on whatever you give it, and the usual failure of the dish is not that it tastes bad but that it tastes like one thing all the way down. Saffron gives the top of the soup something to do.

It also does a different job from the spice most cooks reach for. Turmeric is the standard golden powder here, and it is earthy and slightly bitter in exactly the register the lentils already occupy — you get more colour and more of the same flavour. Saffron pulls the other way, floral and hay-like, and it lifts. We set the two side by side in saffron versus turmeric.

One caution. This pot already carries cumin, paprika and tomato paste, and saffron loses fights with heavy spicing. The quantities below are deliberately restrained on the paprika so there is room for the threads to register.

How much saffron does this need?

Twenty-five threads, roughly 0.10 g, for four to six bowls. Modest by design: thick food coats the tongue and dulls aromatics, so pushing to 50 threads buys a deeper colour and almost no extra smell.

Bloom in plain water rather than broth. Heat 3 tablespoons to about 150°F (65°C) — steaming, still surface, no bubbles — and pour it over the threads for 15 minutes. Water gives the cleanest extraction. Boiling water is the one thing to avoid; it takes the aroma with the steam.

The bloomed liquid goes in off the heat at the very end, threads and all. Stirred in earlier it gets trapped in the starch and simmered away, and you will not be able to find it in the finished bowl. If blooming is new to you, the full method is in how to bloom saffron properly.

Which lentils, and what else?

• 1.5 cups (300 g) split red lentils, rinsed until the water runs clear
• About 25 saffron threads (0.10 g)
• 3 tbsp water, warmed to about 150°F (65°C), for blooming
• 3 tbsp olive oil, plus more to finish
• 1 large onion, finely diced
• 1 carrot, coarsely grated
• 4 garlic cloves, minced
• 2 tsp ground cumin
• 1 tsp sweet paprika
• 1/4 tsp Aleppo pepper, or a pinch of chilli flakes
• 2 tbsp tomato paste
• 6 cups (1.4 L) vegetable or chicken broth, plus more to thin
• 1 tsp fine sea salt, plus more to taste
• Juice of 1 lemon, about 3 tbsp
• Mint leaves or chopped flat-leaf parsley, to finish

How do you make it?

1. Rinse the lentils. Tip the lentils into a sieve and run cold water through them, working your fingers through the pile, until the water coming out is clear. This takes 30 to 45 seconds. The cloudy starch you are washing away is what turns an unrinsed pot grey and gluey.
2. Bloom the saffron. Warm 3 tablespoons of water to about 150°F (65°C) and pour it over the threads in a small bowl. Leave it for 15 minutes. It should turn deep amber; a pale yellow bloom means the water was too cool or the threads are old.
3. Soften the onion and carrot. Warm the olive oil in a 4 quart saucepan over medium heat. Add the onion, grated carrot and a pinch of salt and cook for 8 to 10 minutes, until the onion is completely soft and the first edges are turning gold.
4. Toast the spices. Add the garlic, cumin, paprika and Aleppo pepper and stir constantly for 45 seconds. They should smell nutty and warm. The instant cumin smells sharp or acrid it has burnt, and the whole pot will taste of it.
5. Cook out the tomato paste. Stir in the tomato paste and fry it for 2 minutes, until it darkens from bright red to brick and starts leaving a rusty film on the base of the pan.
6. Simmer the lentils. Add the lentils, broth and salt. Bring to the boil, then drop to a low simmer, set the lid on at an angle and cook for 20 to 25 minutes. Stir the base every five minutes so nothing catches. It is done when the lentils have lost their shape completely and a spoon dragged across the pan leaves a trail that closes slowly.
7. Blend, or do not. For a smooth soup, blitz with an immersion blender for about 30 seconds. For a rustic one, leave it. Either way, thin with extra broth until it pours off the spoon in a ribbon — it will thicken noticeably as it cools.
8. Finish off the heat. Take the pan off the burner. Stir in the bloomed saffron with its threads and the lemon juice, then let it stand for 3 minutes. Taste and add salt until the flavours snap into focus. Serve with a thread of olive oil and torn mint on each bowl.

What goes wrong with red lentil soup?

Skipping the rinse. It is the single step people drop and it costs you both colour and texture: the loose starch clouds the soup, mutes the saffron and makes the whole thing claggy rather than creamy.

Cooking it too thick. Lentil soup sets as it cools, and a pot that looks perfect on the stove is a paste twenty minutes later. Finish it looser than you want to eat it and keep extra broth warm for reheating.

Not enough acid. Lentils are heavy and slightly sweet, and without lemon the soup sits flat no matter how well it is salted. Three tablespoons is a starting point, not a maximum. Add it off the heat so the brightness survives.

A scorched base. Lentils sink and stick, and once the bottom catches the burnt note runs through everything. Stir every five minutes and use a heavy pan rather than a thin one.

And blooming the saffron into the simmering pot instead of into water first. You lose the aroma to the steam and the colour to the tomato. Off the heat, at the end, every time.

Frequently asked questions

Can I use brown or green lentils instead?

Not as a straight swap. Brown and green lentils hold their shape and need 35 to 45 minutes, giving a brothy soup rather than a purée. If that is what you want, add another cup of broth and blend half the pot for body.

Is saffron worth it with this much cumin around?

It is, provided the rest of the spicing stays where it is. Cumin and saffron sit in different places — one is low and earthy, the other high and floral — and they do not compete for the same space. Double the paprika or add smoked paprika, though, and the saffron will vanish.

Does it improve overnight?

The lentils and cumin do; the saffron does not. Refrigerate up to four days and reheat gently with a splash of broth. If the aroma has faded, bloom five more threads in a tablespoon of warm water and stir them through.

What can I use instead of saffron in this soup?

Nothing reproduces it, and it is better to make an honest cumin-and-lemon lentil soup than a bad imitation. Turmeric will give you the colour but not the aroma, and safflower gives you neither. We go through the options, including the ones that partly work, in our guide to saffron substitutes.

Read next

• Saffron chickpea stew — the same weeknight logic with more chew.
• The most common saffron mistakes, several of which happen in soup pots.
• How to buy saffron without paying for stems and dye.
• Saffron chicken soup if you want a clear broth rather than a thick one.