How to Thicken Any Sauce, Soup or Gravy: The Complete UK Guide
The best way to thicken a sauce, soup or gravy depends on what you are cooking. You can simmer it to reduce, stir in a cornflour or arrowroot slurry, cook flour into a roux, blend in vegetables such as potato or lentils, or finish with yoghurt, cream or butter. This guide brings every method together, with amounts, timings and fixes, so you can choose the right one for any dish.
To thicken a sauce, soup or gravy quickly, mix 1 tbsp cornflour with 2 tbsp cold water for every 500 ml of liquid and stir it into the simmering pan for 1 to 2 minutes. For a richer result, cook equal amounts of butter and flour (a roux) before adding liquid. Without starch, simmer uncovered to reduce, or blend in potato, lentils or part of the soup. Add thickener a little at a time and wait a minute before adding more.
Key Takeaways
- Cornflour slurry is the fastest and most reliable fix for most sauces and gravy.
- A roux gives a rich, stable base for white sauces, cheese sauces and gravy.
- Reduction adds no extra ingredients and makes flavour stronger.
- Vegetables, lentils and oats are natural thickeners for soups.
- Never add dry flour or cornflour straight to hot liquid, or it will go lumpy.
The Main Ways to Thicken Any Dish
🔥 Reduce
Simmer uncovered so water evaporates. No extra ingredients, stronger flavour, but it takes 10 to 20 minutes.
🥄 Starch slurry
Cornflour, arrowroot or potato starch mixed with cold water. Thickens in 1 to 2 minutes.
🧈 Roux
Butter and flour cooked together, then liquid added slowly. Rich, stable and classic.
🥔 Purée
Blend part of a soup, or add potato, red lentils, oats or bread, for a natural, filling thickener.
Thickener Amounts and Times
| Thickener | Amount per 500 ml | Time to thicken | Best for |
|---|---|---|---|
| Cornflour slurry | 1 tbsp + 2 tbsp cold water | 1 to 2 min | Gravy, stir-fry sauce, pie fillings |
| Arrowroot slurry | 1 tbsp + 2 tbsp cold water | Under 1 min, off the boil | Fruit sauces, glazes, acidic sauces |
| Plain flour roux | 1 tbsp butter + 1 tbsp flour | 3 to 5 min | White sauce, cheese sauce, gravy |
| Reduction | None | 10 to 20 min | Pan sauces, tomato sauce, stews |
| Potato | 1 small potato, diced | 15 to 20 min | Vegetable soups, chowder |
| Red lentils | 25 g | 15 to 20 min | Soups, dhal, curry |
| Oats | 1 to 2 tbsp | 5 to 10 min | Soups and stews |
| Egg yolk | 1 yolk, tempered | 2 to 3 min, gentle heat | Custard, carbonara, rich sauces |
| Yoghurt or cream | 2 to 3 tbsp | Off the heat | Curries, soups, creamy sauces |
| Cold butter | 1 to 2 tbsp | 1 min, off the heat | Glossy pan sauces |
How to Thicken a Sauce
For most sauces, a cornflour slurry is the quickest choice. Mix the cornflour with cold water until smooth, bring the sauce to a simmer, pour the slurry in while stirring and cook for 1 to 2 minutes. For tomato sauces and pan sauces, simmering to reduce gives a deeper flavour. For a white or cheese sauce, start with a roux. If you want to avoid flour, see our guide on how to thicken sauce without flour.
How to Thicken Soup
Soup is easiest to thicken by blending a third of it and stirring it back in, or by cooking in potato, red lentils or oats. A spoonful of Greek yoghurt off the heat makes it creamy without cream. Read our full guide on how to thicken soup without cream for eight easy methods.
How to Thicken Gravy
Gravy is usually thickened with a flour roux made in the roasting tin, or with a cornflour slurry stirred into the hot stock. Keep whisking as it thickens. If it goes lumpy, our guide on how to fix lumpy gravy shows how to whisk, sieve or blend it smooth.
How to Thicken Curry and Stews
Simmer curry uncovered for 10 to 15 minutes, add red lentils or a spoonful of ground almonds, or stir in yoghurt or coconut milk at the end. For stews, mash a few pieces of potato or vegetable into the liquid, or add a slurry in the last few minutes.
Tip: Starch thickens more as it cools. If you are making sauce ahead, leave it slightly thinner than you want, as it will set as it rests.
Step-by-Step: How to Make a Slurry
- Put 1 tablespoon of cornflour or arrowroot in a small bowl or cup.
- Add 2 tablespoons of cold water and stir until there are no lumps.
- Bring your sauce, soup or gravy to a gentle simmer.
- Pour the slurry in slowly while stirring all the time.
- Cook for 1 to 2 minutes for cornflour, or take arrowroot off the heat as soon as it thickens.
Learn more in our guide to what a slurry is in cooking, and see how cornflour compares to cornstarch.
Step-by-Step: How to Make a Roux
- Melt 1 tablespoon of butter in a pan over a medium heat.
- Stir in 1 tablespoon of plain flour to make a smooth paste.
- Cook for 1 to 2 minutes, stirring, to cook out the raw flour taste.
- Add 250 to 300 ml of warm liquid a little at a time, whisking between each addition.
- Simmer for 3 to 5 minutes until smooth and thick.
Our guide to what a roux is in cooking explains the different types and ratios.
Gluten-Free Ways to Thicken
Cornflour, arrowroot, potato starch and tapioca are all naturally gluten-free, as are reduction, puréed vegetables, lentils and yoghurt. Plain flour is not gluten-free. If you are cooking for someone with coeliac disease, check labels, as some products are made in factories that also handle wheat. Our guide to arrowroot vs cornflour compares the two most popular gluten-free starches.
Common Problems and Fixes
| Problem | Likely cause | Fix |
|---|---|---|
| Lumpy | Dry thickener added to hot liquid | Whisk hard, sieve or blend |
| Tastes floury | Flour not cooked long enough | Simmer for 2 to 3 more minutes |
| Too thick | Too much thickener | Add hot stock or water a splash at a time |
| Went thin again | Starch boiled too long or acid broke it down | Add a little fresh slurry at the end |
| Looks cloudy | Flour or cornflour in a clear sauce | Use arrowroot for a glossy, clear finish |
| Split or grainy | Yoghurt or cream boiled | Take off the heat and whisk in a splash of cold cream |
Always add thickener gradually. It is much easier to add a little more than to rescue a sauce that has turned into paste.
Frequently Asked Questions
What is the quickest way to thicken a sauce?
A cornflour slurry is quickest. Mix 1 tbsp cornflour with 2 tbsp cold water, stir it into the simmering sauce and cook for 1 to 2 minutes.
How do you thicken a sauce without cornflour?
Simmer it to reduce, make a flour roux, or blend in vegetables, lentils or a spoonful of yoghurt.
Is it better to thicken with flour or cornflour?
Cornflour is stronger and gives a glossier finish. Flour gives a richer, more opaque result and works best as a roux.
How much cornflour do I need to thicken 500 ml?
About 1 tablespoon of cornflour mixed with 2 tablespoons of cold water thickens 500 ml to a pouring sauce.
Why does my sauce get thinner after thickening?
Boiling starch for too long, or adding acid such as lemon juice or tomatoes, can break it down. Add a little fresh slurry at the end.
Can you thicken a sauce after it has cooled?
Yes. Warm it back to a simmer, then add a slurry or reduce it further.
Final Thoughts
Every sauce, soup and gravy can be thickened with one of a few simple methods: reduce it, add a starch slurry, make a roux, or blend in natural thickeners. Choose the one that suits your dish, add it slowly, and keep stirring. Use the linked guides above whenever you need more detail on a single method.
