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How to fix lumpy white sauce

Whisk the sauce hard off the heat, and if lumps remain, push it through a sieve or blend it smooth with a stick blender.

How you can tell

  • Small or large lumps of floury paste in the sauce
  • A gritty or uneven texture
  • Dry pockets of flour that haven't mixed in

Why it happens

White sauce, or béchamel, is thickened with a roux of butter and plain flour. When the flour meets hot liquid, its starch swells and thickens the sauce, a process called gelatinisation. If the milk is added too quickly or not stirred in well, the outside of a clump of roux thickens first and seals dry flour inside, forming a lump. Lumps can also form if the roux is left unstirred or the sauce catches on the bottom of the pan.

How to fix it

Option 1Whisk it out

  1. Take the pan off the heat
  2. Whisk vigorously, pressing lumps against the side of the pan
  3. Return to a gentle heat and keep whisking until smooth

Option 2Sieve or blend

  1. Push the sauce through a fine sieve into a clean pan with the back of a spoon
  2. Or blend it in the pan with a stick blender until smooth
  3. Reheat gently, stirring, and check the seasoning

Next time

  • Cook the roux for a minute or so before adding any milk
  • Add the milk gradually at first, stirring each splash in fully before adding more
  • Use a whisk rather than a spoon
  • Keep stirring as the sauce comes to a simmer and thickens
General kitchen guidance, not food-safety advice. If food may be unsafe, for example undercooked meat or anything left out too long, follow the Food Standards Agency and throw it away if in doubt.