How do you thicken a sauce?
There are a few ways to thicken a sauce. Here's how, according to science.
To add texture to meat juices, you can simmer to allow some water to evaporate before simply whisking in fat to make an emulsion.
You can also add gelatine, which comes from animal collagen and is almost entirely protein. This can come from stock made from boiling chicken scraps. When heated, gelatine’s proteins unravel then interweave, causing the liquid to thicken but not solidify. When cooled, the protein strands line up and twist around each other to create a firm gel.
Wheat flour is commonly used to thicken sauces using a process called starch gelatinisation. The flour grains contain partially crystalline granules of starch, which comprises chains of sugar molecules strung together. The secret to starch’s thickening success is its ability to absorb water and form a gel. Heating breaks the bonds between the starch molecules, freeing them up to bond and trap water.
Many sauces start as a roux, a smooth paste made from equal parts of flour and fat, such as melted butter or oil. To make a roux, heat the fat then stir in the flour. For a nutty flavour, continue to cook the roux until it is golden brown. The fat coats the flour particles, preventing them from clumping together so that the starch is fully available to gelatinise.
Adding liquid while heating causes the starch granules to swell and begin the thickening process. The granules eventually burst open to release starch into the liquid, unleashing more thickening power. Stir the sauce continuously so that the starch doesn’t settle at the bottom of the pan to create a lumpy mess.
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For a white sauce with a pouring consistency, try 15g plain flour, 15g fat and 250ml milk. For a thicker sauce, you could increase the amounts of flour and fat to 25g while keeping the milk at 250ml.
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Asked by: Laura Jackson, Norfolk
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Dr Emma Davies is a science writer and editor with a PhD in food chemistry from the University of Leeds. She writes about all aspects of chemistry, from food and the environment to toxicology and regulatory science.
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