How to Make a Roux to Thicken Up Soup

A roux can thicken a sauce or a soup.
A roux can thicken a sauce or a soup. (Image: Jupiterimages/ Images)

A hearty stew or creamy soup depends on a proper roux to develop a thick, velvety broth. Modern roux can use any type of fat -- cooking oils, lard, or even bacon grease. Clarified butter is the traditional fat used in a roux because it doesn't leave behind any fatty scum or alter the flavor of the soup. Lard and bacon fats are used to make roux for regional soups, such as dark gumbo or flavorful bean soup. When combined with flour, the fat becomes a thick paste that can thicken even the thinnest of soup broths.

Things You'll Need

  • Bowls
  • Fat
  • Flour
  • Measuring cups
  • Saucepan
  • Whisk

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Measure equal parts of fat and flour into two separate bowls. Use 2 ounces of fat and 2 ounces of flour for each quart of soup that requires thickening.

Heat the fat in a saucepan over low to medium heat until it melts. Stir constantly so it heats evenly.

Sprinkle in the flour, a little at a time, and whisk it until it combines with the fat. Continue to whisk in the flour until it dissolves into a paste.

Stir the roux constantly as it heats, otherwise it may scorch. Heat on medium heat the roux for about two minutes, or until it becomes a slight off-white, or blond color, for a light traditional roux. Heat over low heat for up to 15 minutes for a dark roux, such as used in creole soups.

Remove the roux from the heat and stir it for an additional two or three minutes, or until it has cooled to a similar temperature as the soup.

Spoon the roux into the soup, a small amount at a time; alternatively you can add the soup very gradually to the roux if it is prepared in a large stockpot. Whisk to combine while heating the soup to a simmer. Simmer the soup for 20 minutes so the roux can thicken it sufficiently.

Tips & Warnings

  • If you use a fat other than clarified butter, your soup may have fat floating on the surface. Skim it off with a spoon before serving.
  • You can also thicken gravies and sauces with roux.


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