Quick answer: Thickening agents are ingredients that give body to sauces, soups, gravies, fillings and desserts. The main groups are starches (flour, cornflour, arrowroot, potato starch, tapioca and rice), roux (flour cooked in fat), beurre manié, proteins such as eggs, gelling agents (gelatine, agar-agar and pectin), gums and modern hydrocolloids (xanthan, guar), and reduction or purée, which thicken without adding anything new.
Choosing the right thickener affects flavour, clarity, texture and how well a dish holds during service. This guide explains how each one works, when to use it and how to avoid common faults.
How thickening works
Most thickeners work in one of three ways:
- Starch gelatinisation: starch granules absorb water and swell when heated, making the liquid thicker.
- Protein coagulation: egg proteins set when heated, binding the liquid around them.
- Gel formation: substances such as gelatine, agar-agar or pectin form a network that traps liquid and sets it.
Reduction is different. It does not add anything; it evaporates water so the flavour and natural body become more concentrated.
Thickening agents at a glance
| Thickener | Type | Result | Typical uses |
|---|---|---|---|
| Wheat flour | Starch | Opaque, stable body | Gravies, stews, béchamel |
| Roux | Starch cooked in fat | Smooth, opaque, stable | Mother sauces, velouté soups, gumbo |
| Beurre manié | Raw flour and butter paste | Quick, glossy finish | Adjusting sauces and stews at the end |
| Cornflour (cornstarch) | Starch | Glossy, fairly clear | Stir-fry sauces, custards, fruit sauces |
| Arrowroot | Starch | Very clear and glossy | Fruit glazes, clear sauces |
| Potato starch | Starch | Clear, strong thickening | Soups, gluten-free baking |
| Tapioca | Starch | Clear, slightly elastic | Pie fillings, puddings |
| Egg yolks (liaison) | Protein | Rich, velvety | Velouté soups, custards, sauces |
| Gelatine | Gelling (animal) | Soft, wobbly set; melts in the mouth | Mousses, panna cotta, jellies |
| Agar-agar | Gelling (seaweed) | Firm set; stable at room temperature | Vegetarian jellies, terrines |
| Pectin | Gelling (fruit) | Jam-like set with sugar and acid | Jams, jellies, fruit pastes |
| Xanthan / guar gum | Gums | Thickens cold or hot in small amounts | Dressings, gluten-free baking, modern sauces |
| Reduction | Evaporation | Concentrated flavour and body | Jus, glazes, pan sauces |
| Purée | Ingredient-based | Natural, rustic body | Purée soups, vegetable sauces |
Starch thickeners
Wheat flour
Flour is the most common thickener in Western cooking. It gives an opaque, stable result that holds well on a hot counter. Raw flour tastes pasty, so it must be cooked out, either in a roux or by simmering the sauce for long enough after it thickens.
Cornflour
Cornflour is pure starch from maize. It thickens strongly, gives a glossy and fairly clear finish, and is widely used in Chinese and Indo-Chinese cooking. Mix it with cold water first (a slurry) and stir it into a simmering liquid. Cornflour sauces can thin again if they are stirred hard or held too long.
Arrowroot
Arrowroot gives a very clear, shiny finish, which makes it ideal for fruit glazes and delicate sauces. It thickens at a lower temperature than cornflour, but it does not hold well with long cooking or reheating, and it can turn slimy with dairy.
Potato starch, tapioca and rice flour
Potato starch thickens quickly and clearly and is useful in gluten-free cooking. Tapioca gives a slightly elastic texture that suits fruit pie fillings. Rice flour is the traditional thickener for bisques and is also used in many Asian dishes.
Roux and beurre manié
Roux
A roux is equal parts of fat and flour by weight, cooked together before liquid is added. Cooking the flour in fat coats the starch and stops lumps forming when the liquid goes in.
| Roux | Cooking | Colour | Used for |
|---|---|---|---|
| White roux | Briefly, without colour | White | Béchamel |
| Blond roux | A little longer, until sandy | Pale straw | Velouté sauces and soups |
| Brown roux | Slowly, until nutty brown | Brown | Espagnole and brown sauces |
The darker a roux, the more flavour it has but the less thickening power, because some of the starch breaks down as it browns. For a smooth sauce, add cold liquid to a hot roux or hot liquid to a cooled roux, whisking constantly. You can see how each roux leads to a classic sauce in our guide to the five mother sauces.
Beurre manié
Beurre manié is a paste of raw flour and soft butter kneaded together. Small pieces are whisked into a simmering sauce at the end of cooking to adjust its thickness. The butter separates the flour particles, so the paste does not form lumps. Simmer briefly afterwards to cook out the raw flour taste.
Egg-based thickening
Egg yolks thicken and enrich custards, sauces and soups. A liaison of egg yolks and cream is the classic finish for a velouté soup. Eggs set at a much lower temperature than starch thickens, so they curdle if overheated.
- Temper the yolks by whisking in a little hot liquid before adding them to the pan.
- Keep the mixture below boiling once yolks are added.
- Custards that contain some flour or cornflour, such as pastry cream, can be boiled because the starch protects the eggs.
Gelling agents
- Gelatine comes from animal collagen. It is soaked (bloomed) in cold water, then dissolved in warm liquid. It gives a soft set that melts at body temperature, which is why panna cotta feels so smooth. It is not suitable for vegetarians.
- Agar-agar comes from seaweed. It must be boiled to activate, sets firmly and stays set at room temperature, which makes it useful for buffets and vegetarian dishes.
- Pectin occurs naturally in fruits such as apples and citrus. It needs the right balance of sugar and acid to set jams and jellies.
Some raw fruits, such as pineapple, kiwi and papaya, contain enzymes that break down gelatine. Cook the fruit first, or use agar-agar instead.
Gums and modern thickeners
Xanthan gum and guar gum thicken in very small amounts, work cold as well as hot, and help hold dressings and sauces together. They are common in gluten-free baking and in commercial food production. Use them sparingly; too much gives a slimy texture.
Thickening without additives
- Reduction: simmering a stock or sauce to evaporate water, as in a jus or demi-glace.
- Purée: blending cooked vegetables or pulses into the liquid, as in purée soups. See our classification of soup guide for examples.
- Emulsion: whisking butter or oil into a sauce, as in beurre blanc, gives body as well as richness.
- Breadcrumbs, nuts and seeds: traditional thickeners in many regional dishes, including ground cashew and poppy seed pastes in Indian gravies.
Common problems and fixes
| Problem | Cause | Fix |
|---|---|---|
| Lumpy sauce | Starch added directly to hot liquid | Use a slurry or roux; strain or blend the sauce |
| Floury taste | Flour not cooked long enough | Simmer longer after thickening |
| Sauce thins on standing | Over-stirred cornflour or arrowroot, or acid breaking the starch | Use a more stable starch such as flour for long holding |
| Curdled custard | Eggs overheated | Strain at once into a cold bowl; blend if needed |
| Jelly will not set | Too little gelatine, or raw enzyme-rich fruit | Check quantities; cook the fruit or switch to agar-agar |
Frequently asked questions
What are the main types of thickening agents?
Starches (flour, cornflour, arrowroot, potato starch, tapioca, rice flour), roux and beurre manié, eggs, gelling agents (gelatine, agar-agar, pectin), gums (xanthan, guar), and methods such as reduction and purée.
What is the difference between a roux and beurre manié?
A roux is fat and flour cooked together before liquid is added. Beurre manié is raw flour and butter kneaded into a paste and whisked in at the end to adjust thickness.
Which thickener gives a clear sauce?
Arrowroot gives the clearest finish, followed by potato starch and cornflour. Wheat flour gives an opaque sauce.
Is agar-agar a substitute for gelatine?
Yes, for vegetarian dishes. It must be boiled to activate and gives a firmer set that stays stable at room temperature, so quantities and method differ from gelatine.
How do you thicken a sauce without flour?
Reduce it, blend in a vegetable purée, use cornflour or arrowroot, or finish with egg yolks or cold butter, depending on the sauce.
Why did my cornflour sauce turn thin?
Cornflour sauces can thin if they are stirred too vigorously, cooked for too long, or combined with a lot of acid. Add it near the end and stir gently.