Found across hundreds of sauce recipes, roux helps thicken liquids into sauces. From milk to create Bechamel to Stock to create Velouté, incorporating Roux to your sauces will dramatically transform its texture and appearance.
Before getting into the details, we need first to answer one important question: What is Roux? Roux is a mixture of equal parts of fat and flour which is used as thickening agent.
You can elaborate Roux using many different fats like butter or light vegetable oils. Plain white flour is recommended for most of the elaborations as it will produce a paste with uniform colour, which is way more appealing and versatile.
All Roux (White, Blonde, Brown) are prepared in the same way; the only difference is for how long we'll leave the mixture of butter and flour browning under medium heat.
For cooking a white roux, add your flour to the melted butter and cook for approximately 2-3 minutes until the paste becomes slight blonde. White roux is typically used in white sauces such as bechamel.
Instead of removing the paste after 2-3 minutes, keep stirring for up to 5-6 minutes until the colour is intense Blonde. Once ready, it'll start to smell a bit to popcorn. Blond Roux is typically used in Veloute sauces.
Leave the mixture cook for 8-10 minutes until the colour becomes brown-ish. If you taste it, you'll notice bready flavours. Brown roux is mostly used in dark sauces such as Espagnole.
You can use your roux while it is warm, but make sure it is not hot (straight from the pan) Why should I let it cool? because it is quite likely you'll add your roux into liquids which are hot. By integrating hot roux into a hot liquid, you risk your roux from breaking, losing it's thickening power and causing lumps.
To thick your sauces use approximately 100g/150g/200g of roux per litre of liquid depending on the consistency you are looking for. 100g will make your sauce have body, but still be thin, 200g will make your sauce quite thick and creamy.
When using brown roux, you'll need to incorporate a bigger proportion to achieve the same thickness than with the other two. That is because while cooking it, many more starches would have broken.
Once you add your roux, you need to whisk your sauce vigorously to incorporate it fully. Once it is incorporated, let the sauce simmer for 5-10 minutes. While it is simmering the roux will do its job and thick the sauce. If the consistency is not the one you are looking for, remember that you can always incorporate more roux or more liquid (milk, water, stock) until you achieve your desired texture.
You can safely keep your cooked roux in the fridge for up to 2 weeks. Remember to use a closed container, so it doesn't catch any flavours from the refrigerator.
You can freeze your roux for up to 3 months. Remember to bring it to room temperature before using it.