You can thicken a sauce in six ways, and every way tastes different. Reduction, roux, starch, egg yolk with cream, butter or a purée: choosing between those six is half the work of a saucier. Whoever knows them can rescue any sauce that is too thin, and knows which one suits which dish.
A thickener is anything that makes a liquid thicker, smoother or more bound. One works by letting moisture evaporate, another by letting starch swell, and yet another by dispersing fat finely. Each gives its own texture, shine and flavour.
The six ways at a glance
| Thickener | How does it work? | Result | Watch out |
|---|---|---|---|
| Reduction | letting moisture evaporate | concentrated flavour, light shine | watch the salt, it gets saltier |
| Roux | starch in fat | firm, creamy sauce | let it simmer for 10 to 15 minutes |
| Starch | starch in cold liquid | glossy, clear sauce | boil briefly, not too long |
| Liaison | egg yolk with cream | rich, smooth sauce | not above 80 °C, otherwise it splits |
| Butter (monter) | whisking in cold butter | shine and roundness | off the heat, don’t boil the sauce again |
| Purée | fine pieces in the liquid | rough to smooth sauce | colour and flavour of the purée |
Reduction
Reduction is the simplest way: you let a sauce or stock simmer gently without a lid, so the water evaporates and the flavour becomes concentrated. You don’t need to add anything. Reduce over medium-high heat, in a wide pan, because a large surface evaporates faster.
A good reduction is ready when the sauce coats a spoon: draw a line with your finger across the back of the spoon. If the line stays, it is thick enough. Salt only at the end, because the salt stays behind while the water disappears.
Roux and beurre manié
A roux is equal parts butter and flour, briefly cooked and then turned into a sauce with liquid. It gives a firm, creamy thickening, and is the base of béchamel, velouté and espagnole.
Beurre manié is the quick variant for those who want to thicken a sauce afterwards. Knead equal parts of soft butter and flour into a paste, roll small balls from it and whisk them one by one into the simmering sauce. Then let the sauce simmer for a few more minutes.
Starch
Cornflour, potato starch and arrowroot are pure starches. They give a clear, glossy thickening without fat. Always mix the starch first with cold liquid into a smooth paste, the so-called slurry, and then pour that into the simmering sauce while stirring.
| Starch | Guideline per 250 ml | Property |
|---|---|---|
| Cornflour | about 1 tablespoon | versatile, allows boiling |
| Potato starch | about 1 tablespoon | thickens fast, don’t boil long |
| Arrowroot | about 1 tablespoon | clear and acid-resistant |
Starch thickens almost immediately. Don’t boil for too long: some kinds, such as potato starch, lose their thickening power when they boil long.
Liaison: egg yolk and cream
A liaison is a mixture of egg yolk and cream with which you thicken and enrich a sauce at the end. It gives a velvety, rich texture. You must do it carefully though, because egg yolk curdles at high temperature: the proteins set and you get scrambled egg in your sauce.
- Beat 1 to 2 egg yolks loose with 50 ml of cream.
- Take the pan with the sauce off the heat.
- Stir a few spoonfuls of hot sauce into the yolk mixture to temper it.
- Pour the mixture back into the pan and whisk quickly.
- Heat gently until the sauce thickens, but don’t let it boil again: keep it under about 80 °C.
Liaisons are classical in a blanquette, a velouté and certain soups.
Whisking in butter: monter au beurre
As the last step whisk a few cubes of cold butter into the hot sauce taken off the heat. The butter emulsifies and gives the sauce shine, roundness and a nice, smooth texture. Put the pan off the heat and don’t let the sauce boil again afterwards, because then the butter separates.
This technique is related to the cold and warm emulsions.
Purée
Puréed vegetables, pulses, nuts or bread thicken a sauce without adding anything extra. Think of a tomato sauce of which you blend the pieces, a soup in which you purée potato along, or a sauce with roasted pepper. It also gives flavour, colour and nutritional value.
Which do you choose when?
| Situation | Best choice |
|---|---|
| A creamy sauce with meat or fish | roux or liaison |
| A clear gravy with a roast | reduction, possibly a little starch |
| A quick fix | starch or beurre manié |
| A luxurious finish | whisking in butter or liaison |
| A healthy, light sauce | purée or reduction |
| For people without gluten | cornflour, potato starch or purée |
The most common mistakes
You add starch straight to the hot sauce
It clumps straight away.
Solution: mix it first with cold liquid into a smooth slurry.
You let the liaison boil
The yolks curdle.
Solution: keep the sauce below 80 °C and heat it gently.
You salt before reducing
The sauce becomes too salty.
Solution: salt only at the end of the reduction.
You use too much of one thickener
The sauce becomes sticky or pasty.
Solution: add little by little and taste.
You boil the monter-finished sauce
The butter separates.
Solution: keep the sauce warm after monter, but don’t let it boil again.
Rescuing a sauce
- Too thin: reduce it further or thicken it with slurry or beurre manié.
- Too thick: dilute with warm stock or milk.
- Lumps: whisk vigorously, strain or use a stick blender.
- Split: slowly whisk in a little cold water or a fresh egg yolk.
- Too salty: dilute with unsalted liquid or cream. A piece of raw potato does not take the salt out.
Practise with a gravy
- Brown some meat or bones and deglaze with stock.
- Strain the liquid and reduce for 10 minutes.
- Mix 1 teaspoon of cornflour with cold water.
- Pour the slurry into the simmering gravy while stirring.
- Let simmer for 1 minute and taste.
You see straight away how a sauce goes from watery to bound and glossy.
Frequently asked questions about thickeners
What is the difference between cornflour and flour?
Cornflour is pure starch and thickens more strongly than flour. It gives a clear, glossy sauce. Flour also contains gluten and protein, and gives a firmer, matte sauce.
Can I thicken a sauce afterwards?
Yes. Slurry or beurre manié work in a few minutes. Add little by little and let it simmer.
Why does my sauce become slimy?
Usually it has been boiled too long with starch, or too much has been used. Use less and boil for less time.
Which thickener is gluten-free?
Cornflour, potato starch and arrowroot, reduction, butter and purée are gluten-free. Roux and beurre manié contain flour and therefore gluten.
Can I reheat a sauce with liaison?
Preferably not. Heat it very gently, stirring, and don’t let it boil. Otherwise it splits easily.
Thickeners at a glance
- There are six ways: reduction, roux, starch, liaison, butter and purée.
- Reduction gives concentrated flavour, salt only at the end.
- Always mix starch with cold liquid first.
- Keep a liaison under 80 °C.
- Whisk in butter off the heat and don’t boil afterwards.
- A purée thickens and gives flavour.
- Each thickener gives its own texture.
Remember this
Thickening is not just making thicker. It is about the texture, shine and flavour you want. Whoever knows the six ways chooses consciously and can adjust any sauce. It isn’t about one perfect thickener, but about control.