When making a stew, I forgot to add flour before the liquid. To thicken the stew, I added some slurry (flour + cold water). However, it was not enough. I would add more slurry, but I found this website (2012) that says

If you've prepared a dish that started out with a roux and you feel it needs a slurry at the end for additional thickening: use cornstarch or arrowroot to prepare the slurry. Why? Because a chemical reaction occurs that will prevent the same starch used twice to thicken it any further.

I could find not any other sources supporting or opposing this claim, so I'll ask here:

Can I thicken a sauce/stew twice with flour (roux+slurry or slurry+slurry)?

  • 2
    You don't need flour for the thickening (and it can leave a bit of a raw flour flavor if you add too much). I shred a potato into the hot stew, and it'll dissolve into the liquid but release its starch. Instant potato flakes also work well.
    – Joe
    Oct 26, 2019 at 17:23
  • This initially sounded like complete nonsense to me (an Australian), because in Australia Corn Flour is normally made of Wheat; and so would be the same starch. Then I checked cooking.stackexchange.com/questions/784/… and saw that in the other listed countries it is infact made of various parts of the corn. Oct 27, 2019 at 12:44

2 Answers 2


A reaction that prevents starch from the same plant thickening if you add it later instead of all at the same time seems very unlikely. And anyway, a roux could be made with non-wheat flour even though it's not traditional - what do they think would happen then? Or if you make a roux on another pan and add that. I can confirm that works.

There is a good reason not to add a slurry late in cooking - the raw flour flavour it imparts. That's why I'd use cornflour (corn starch) for late thickening.

  • 5
    I completely agree, the chemical reaction thing is complete hooey.
    – GdD
    Oct 26, 2019 at 12:09
  • 1
    If you don't have cornstarch handy you could cook the slurry in a separate pan before adding it to the pot to cut down on the raw flavour.
    – Dugan
    Oct 28, 2019 at 20:12

If you want to thicken a stew at the end of the cooking process, I've found that the best option is to use a buerre manie. Mix together equal parts flour and room-temperature (not melted) butter, and whisk that into your stew.

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