Gluten-free sauces and gravy: slurries, roux and fixes
Most traditional sauces and gravies are thickened with a wheat flour roux, so going gluten-free means choosing another route. There are two main ones. A starch slurry is a gluten-free starch stirred into cold liquid and added to a simmering sauce. A gluten-free roux cooks a flour such as rice flour or sorghum flour in fat, then adds liquid. They behave differently, taste differently and suit different dishes. This guide explains how each works, how to avoid lumps, and how sauces behave when they are reheated or frozen. For a full comparison of cornstarch (cornflour in the UK; in Australia and New Zealand check it is maize, not wheaten, cornflour), arrowroot, tapioca and potato starch, see the thickeners guide, which this page does not repeat. All of this is written to also work for vegan cooking: use oil or plant-based butter in place of dairy butter, and a vegetable stock or plant milk as the liquid.
Two ways to thicken
| Starch slurry | Gluten-free flour roux | |
|---|---|---|
| What it is | A starch mixed with cold water, stirred into a hot liquid | Flour cooked in fat, then liquid whisked in |
| Look | Often glossy and smooth, ranging from clear to slightly cloudy depending on the starch | Opaque, creamy and matt |
| Flavour | Neutral, so the sauce tastes of its ingredients | Rounded and slightly toasty, more so when the roux is cooked longer |
| Speed | Fast, thickens within a minute or two of simmering | Slower, as the roux is cooked first and the sauce simmers afterwards |
| Best for | Stir-fry sauces, quick pan sauces, fruit sauces, clear gravies | Creamy white sauces, gravies with body, cheese-style sauces and gratins |
| Watch for | Thinning if boiled hard or left a long time, and weeping when frozen | Grittiness if the flour is not cooked and simmered long enough |
Neither is better in every situation. A slurry is the simplest fix and suits a sauce that is mostly finished. A roux builds body from the start and suits a sauce that should taste rich and creamy.
Making a slurry
Stir the starch into an equal or slightly larger amount of cold water until it is completely smooth, with no dry pockets. Pour it into a simmering, not violently boiling, sauce while stirring, then keep stirring and let it come back to a gentle simmer for a minute or so. Starch granules swell and thicken as they are heated in liquid, and the sauce reaches its full thickness only once it has come back to a simmer. Add a little at a time rather than all at once, since it is easier to thicken more than to thin.
Starting amounts, differences between starches and fixes for lumps, thinning and weeping are in the thickeners guide. The key points for sauces and gravies are to use cold liquid for the slurry, never to sprinkle dry starch into hot liquid, and to season and add acid such as lemon juice or vinegar at the end where you can.
Making a gluten-free roux
A roux works the same way as in wheat cooking. Melt oil or vegan butter, whisk in flour, cook it briefly while stirring, then add warm liquid gradually while whisking. A common starting point is the same weight of fat as flour, with the quantity of liquid adjusted for how thick you want the sauce. Gluten-free flours do not behave exactly like wheat flour, so treat any ratio as a starting point and adjust.
- Rice flour (white or brown) gives a smooth, neutral sauce. White rice flour is the usual choice for pale sauces.
- Sorghum flour adds a mild, slightly sweet and nutty flavour, which suits gravies and darker sauces. It is often combined with rice flour.
- A readymade gluten-free plain flour blend works too, but blends containing xanthan gum or starches may thicken a little differently. Check what is in yours.
- Cook the roux for a few minutes. Rice flour in particular should be cooked well so that it does not taste raw or leave a grainy texture.
Add the liquid gradually and warm if possible, whisking continuously. A pale roux gives a white sauce; cooking it longer to a golden or light brown colour gives a gravy a deeper, toasted flavour. A darker roux generally thickens a little less than a pale one, so you may need to simmer longer or add more.
Avoiding lumps
| Cause | Fix |
|---|---|
| Dry starch sprinkled into hot liquid | Always mix starch with cold water first, and stir it again just before adding it, because it settles |
| Liquid added to a roux all at once | Add warm liquid a little at a time, whisking after each addition until smooth |
| Pouring in too quickly without stirring | Stir constantly while pouring |
| Flour clumped in the fat | Break up the flour in the fat before the heat is high, then cook while stirring |
| Lumps already formed | Whisk hard, use a stick blender, or pass the sauce through a sieve |
A fine sieve is the dependable rescue for a sauce that is otherwise good. A stick blender smooths a roux-based sauce quickly, though it can make some starch-thickened sauces slimy, so use it briefly.
Reheating
Thickened sauces can change as they cool and sit. A starch sauce often sets to a thicker gel in the fridge, and it may look thick or lumpy until it is warmed. Reheat gently, stirring, and add a splash of water, stock or plant milk to loosen it. Avoid boiling hard or heating for a long time, since long heat and strong stirring can break down some starches and leave the sauce thin. If it is still thin after reheating, stir in a small fresh slurry and bring it back to a simmer. A sauce made with a roux is often more forgiving to reheat, but it also thickens as it stands, so loosen it with a little liquid and whisk.
Freezing
Freezing is where starch sauces most often go wrong. Some starch gels release water on thawing, giving a sauce that looks separated or watery. Choosing a starch that tolerates freezing is covered in the thickeners guide. Wheat-flour roux sauces are often said to freeze acceptably; with a rice-flour or sorghum roux expect more separation on thawing, which usually comes back with a thorough whisk over low heat. Cool the sauce before it goes into the freezer, in a labelled airtight container, leaving a little room for expansion. Thaw it in the fridge, reheat gently, and whisk. If you intend to freeze a dish, it can be worth thickening it a little less and finishing it after reheating.
Sauces enriched with plant cream or plant milk may separate on freezing as well. Whisk or blend them smooth when you reheat them.
Gravy and labels
Gravy granules, stock cubes, sauce mixes and soy sauce frequently contain wheat or other gluten ingredients, so check each one for a gluten-free label. The soy sauce and tamari guide covers swaps for the common condiments. For coeliac disease and allergies, general information is no substitute for reading labels and following the advice of your doctor, dietitian or national coeliac society.
What this guide is based on
- How starch granules swell and thicken liquid when heated, why dry starch lumps in hot liquid, and the basic method for a slurry and a roux (fat and flour cooked together, then liquid added gradually) are general cooking knowledge.
- Equal weights of fat and flour for a roux is a widely published starting point, not a result from our own test cooking. Gluten-free flours and blends vary, so amounts are not from our own testing and should be adjusted.
- Statements about flavour (rice flour neutral, sorghum mild and nutty), reheating and freezing reflect widely reported behaviour and will vary by flour, starch and recipe.
- Gluten, coeliac and allergy remarks are general. Check labels and ask a doctor, dietitian or coeliac society about your own needs.