Sometimes when I make a roux-based sauce, it turns out too thin. Are there any ways to make it thicker after the sauce is done? Adding salt helps a bit, but I don't want to add too much for obvious reasons. Ideas how to prevent the sauce from getting too thin in the first place are also welcome.

  • 5
    I have no idea how salt would do anything other than make your sauce more salty. I wouldn't expect it to affect the viscosity at all.
    – Allison
    Commented Mar 11, 2011 at 12:21
  • Are you cooking it long enough, it can take a while to thicken
    – vwiggins
    Commented Mar 11, 2011 at 12:27

6 Answers 6


If your sauce is too thin, the problem is that your initial roux was either too thin (not enough flour) or you added too much liquid for the amount of roux that you made. Standard ratios are 1 Tbsp butter - 1 Tbsp flour - 1 cup liquid for a thin sauce, 2-2-1 for something in the middle and 3-3-1 for a thick sauce.

Once you've made the sauce and it's too thin, the best fix is to add a beurre manié, which is essentially butter and flour that you mash together in a small bowl and then whisk into your sauce. It's kind of like adding more roux after the fact. However, because it's not pre-cooked like the roux, you need to make sure you give it enough cooking time after adding to get rid of the floury taste.


As an alternative to corn flour, Arrowroot is a plant based starch of similar price to corn starch but with some better qualities

Important is sauces is that it does not cloud the sauce, and keeps a shiny appearance

Also, it doesn't require the heat level to set that corn starch does. So it can be added after a sauce is finished to increase thickness

Always mix Arrowroot with a little cold liquid (not milk) and then add that to the sauce

  • 2
    Agreed on arrowroot being a superior choice to corn starch in many cases; however, I don't think I'd use either in a roux. Arrowroot also has no protein, so it won't really "cook" or gelatinize like wheat flour, and it also breaks down under high heat, which a roux will tend to be subjected to. There's a lot to be said for choosing the appropriate flour for a specific roux based on protein content, but a roux made with no protein is going to be thin, flat, and flavourless.
    – Aaronut
    Commented Mar 11, 2011 at 16:59
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    @Aaronut The OP wanted "Are there any ways to make it thicker after the sauce is done?" A roux is made with flour, but if the finished product is too thin, Arrowroot is a quick fix
    – TFD
    Commented Mar 11, 2011 at 20:54
  • I understand. The first few words were "as an alternative" so I assumed you meant to use it instead of flour. Presumably that must have been in reference to the corn starch answer instead.
    – Aaronut
    Commented Mar 11, 2011 at 21:23
  • @Aaronut ah yes, that is a technicality with SE, it reads in a different order every time you view a page. Have edited to by crystal clear
    – TFD
    Commented Mar 12, 2011 at 10:39
  • 1
    Only for answers with tied votes. The highest-voted answer is always at the top.
    – Aaronut
    Commented Mar 12, 2011 at 15:57

One excellent way to thicker almost any type of sauce is to use corn flour. It is inexpensive and easy to use. When you've decided you want to thicken your sauce separately mix some cornflower with a little milk or water to make a smooth paste and then add to you sauce making suer you stir. This works well for soups too.

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    Thanks. Is there a particular reason to use cornflour instead of ordinary flour? Commented Mar 11, 2011 at 9:51
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    Cornflour works faster, and I find it gives a smoother, less floury taste. Whisk or stir constantly as you add it though, otherwise you'll end up with lumps.
    – KimbaF
    Commented Mar 11, 2011 at 9:57
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    Cornflour, is not a 'flour' it is the processed starch from corn meal. While wheat or corn meal flour will thicken sauces, you need a lot more product to get the same thickening level, and this will effect taste and quality
    – TFD
    Commented Mar 11, 2011 at 11:16
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    What the UK calls cornflour, the US calls cornstarch. (corn flour in the US is frequently a finer grind of cornmeal, used for making tamales and the like) see cooking.stackexchange.com/questions/784/…
    – Joe
    Commented Mar 11, 2011 at 13:38
  • While this is true in a general sense, I feel that it's kind of irrelevant to the specific question. A roux is, by definition, made from fat and starch, so either you are saying "use more flour", which is pretty self-evident, or "use corn starch instead of regular flour", which as @TFD says, is actually not a flour and thus not such a hot idea for a roux; you won't get the rich flavour you're supposed to get from cooked flour.
    – Aaronut
    Commented Mar 11, 2011 at 16:53

A quick solution is to make a slurry. Add 1 tbsp flour to 1/4 cup liquid and stir til combined, if too thick add a little more cold liquid. BTW, if you add hot liquid it will expand too quickly. Once it is thinned out enough, add to the pot and whisk together. When it is thick enough, add equal extra amount of butter or oil to balance flavour.


If you have this problem frequently, one solution is to make more roux than you think you'll need, then reserve some after you've cooked it, but before you've added any (or much) liquid;

You can then add the roux in at the end ... the easiest way is to get some onto a wisk and then wisk it in, and keep repeating until you think you've gotten enough in.

It will thicken up with time if you leave it at a simmer, but I think that might be partially from evaporation, so you'll end up with less. It'll also thicken up more as it cools down, so you want it a little thinner than the thickness you want to serve it at, or it might turn into a giant lump.

  • Very likely due to evaporation. A roux actually has a pretty small margin of error; too little water and the flour won't gelatinize, too much water and you'll end up with slurry. Normally one of the things you need to be extra careful of when making a roux is letting the water evaporate too quickly; if the roux balls up (i.e. is cooked) and is still too thin then it means you added way too much water at the beginning - better to just use less water next time than to try to "reduce" it afterward and risk overcooking the roux.
    – Aaronut
    Commented Mar 11, 2011 at 17:03

The best way that I've found to keep the roux from being too thin is to slowly add the liquid, letting the roux thicken as it cooks. When it starts to get thick and I need more volume, I'll add more liquid. Repeat until the required volume is reached. Depending on what I'm making it for, I might add more butter and/or flour.

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