How to Thicken Soup
Eight ways to fix thin soup and when to use each method.
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Soup is a dish that lends itself to all the seasons and is a go-to comfort food. But it can be disappointing when the soup turns out thin and you’re faced with the uncertain task of how to thicken it. For more info on why this happens and different ways to thicken soup, we consulted Nathaniel Sloan, chef-owner of bloom, a restaurant and wine bar in Roanoke, VA, and Billy Cotter, co-owner of Toast Paninoteca in Durham, NC.
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Why Is My Soup Thin?
Soup can be thin for a variety of reasons including water content, certain ingredients such as fat, acid or sugar, and not reducing it for enough time.
Water Content
Soups may be thin because they have a high water content, which can result from liquids added to base ingredients, such broth, stock or water, or ingredients with higher water content.
“Your soup can turn out too thin if the ratio of solids to liquids was unbalanced, especially true with vegetable soups because the vegetables themselves contain a fair amount of liquid,” Cotter says. Sloan echoes than sentiment, and notes that vegetables such as summer squash, greens, onions and fruit have a particularly high water content.
Ingredients
Some ingredients can alter the thickness of soup, including fat, acid or sugar. “An alternative reason why a soup could start thick and end thin is the de-naturing of proteins,” Sloan says. “A good example of this is when acid (such as vinegar or citrus juice) is added to a dairy-based soup and the soup is heated to a high temperature.”
Cotter adds that, “For soups with pork, beef, lamb, etc. it could be that the soup did not simmer long enough to release the fats and natural gelatins.”
Not Reducing It Enough
Many soup recipes call for reducing the soup to allow liquid to evaporate and thus thicken the consistency. “Another common mistake when making soup is not allowing enough evaporation of liquid to occur, thus rushing the process,” Sloan says. “A lot of soups call for the power of reduction and concentration of flavor to make them what they are known to be.”
8 Ways to Thicken Soup
Method 1: Make a Starch-Based Slurry
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About this method:
A 2-to-1 ratio of cold water to starch—such as corn, potato, arrowroot, or tapioca starch—are whisked together to make a slurry. When the starchy slurry is added to the hot soup, the starch granules swell and gelatinize which causes the mixture to thicken.
When to use this method:
A starch-based slurry can help thicken a variety of soups, including cream-based soups, pureed soups, gumbos and chowders.
What to do:
Make a starch slurry by whisking together 2 parts cold water to 1 part vegetable starch of your choice, including corn, potato, arrowroot or tapioca. Drizzle into the hot soup a little at a time and whisk continuously to combine, then bring to a boil to achieve the desired consistency, cooking for about 5 minutes.
Another example of a vegetable starch thickened soup is “a Choctaw gumbo where filé (ground sassafras) is added at the end of the cooking process to aid in flavor and mouthfeel,” Sloan says.
Method 2: Make a Roux
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About this method:
A roux is a combination of equal parts (by weight) flour and fat, cooked together to form a paste. “With the roux method, you melt a fat of your choosing, add sifted flour, and then incorporate your heated liquid base, generally stock or broth,” Sloan says.
When to use this method:
A roux is one of the most common ways to thicken a variety of soups, particularly gumbo and creamy soups. “A classic roux is great for making soups where gluten is not an issue, and a thick viscosity is desired,” Sloan says. “One of the most common examples of this is French onion soup where you melt butter, sweat onions, garlic and thyme, and then add your concentrated beef broth.”
What to do:
To make a roux, heat butter or other fat in a saucepan, then add flour and stir or whisk to form a paste. Cook over medium heat for a few minutes, until the raw flour taste is cooked out; the roux should have a stiff texture.
“For gumbos and Low Country-style soups, you should start with a roux of equal parts flour and oil or butter. Just be sure you cook it long enough on low heat to cook the raw flavor out of the flour,” Cotter says. “Gumbo in particular requires the roux to be cooked slowly, stirring constantly, until it’s the color of dark peanut butter.”
Method 3: Make a Beurre Manié
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About this method:
Beurre manié is similar to a classic roux, but as Sloan explains, “instead of cooking the butter and flour in the stock pot at the beginning, you knead soft butter and flour together to form what becomes a springy paste.”
When to use this method:
In addition to helping to thicken a variety of soups, it can add a luxurious mouthfeel to creamy soups and chowders.
What to do:
Make a butter-flour paste by kneading or using a fork to incorporate equal parts softened, unsalted butter and all-purpose flour. Gradually add the paste pieces to the hot soup and bring to a boil and cook to ensure that the flour taste is cooked out and until the soup fully thickens.
Method 4: Puree
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About this method: You can puree some of your soup to thicken it, particularly if the soup already incorporates components that would blend well, such as beans, lentils or potatoes.
When to use this method: Bean, lentil or vegetable soups, especially potato-based soups, and gluten-free soups.
“We take a portion of our bean/lentil soups, purée them, and add it back to the pot for body,” Cotter says. “It gives them a great texture and thickness.” Sloan is a fan of using potatoes to thicken soups. “The humble potato has an amazing amount of thickening power, and is also an excellent gluten free option,” he says.
What to do:
To use beans or lentils to thicken soup, simply blend about a cup or so of the soup (including the cooked beans or lentils) until smooth, then add it back to the pot to achieve an ideal consistency.
If using potatoes to thicken soup, Sloan advises slow-cooking the potatoes alongside the soup and other ingredients in a liquid of your choosing, then pureeing the soup while warm. “Please note, do not over puree or over reduce the liquid [because] the potato starch is strong and can become quite unpleasant or "gluey" if you are not careful,” Sloan says. “A great example of a potato thickened soup is the fan favorite- potato and leek.”
You can also puree cooked potatoes into the finished soup. “For a puréed soup that’s too thin, you can cook some potatoes in salted boiling water until tender, drain, and blend them into the soup,” Cotter says. “You’ll have to check your seasoning for salt because the potatoes will pull some of the flavor out.”
Method 5: Add Pasta, Grains or Bread
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About this method:
Adding pasta or cooked grains such as rice or barley to a pot of soup can help release starches into the soup and help thicken the consistency. Finishing a soup with croutons or reheating it with bread is another starchy way to thicken soups.
When to use this method:
Brothy soups such as chicken soup or minestrone. “The addition of pasta or (cooked) rice to a soup when the cooking process is almost complete is another fun way to add viscosity and depth,” Cotter says.
What to do:
If thickening the soup with cooked pasta or grains: add just before the end of cooking and let simmer for a few minutes. “If you are making a brothy vegetable soup like a minestrone, you don’t necessarily need to have a thick liquid but if the ratio of liquid to vegetables is too high, you can cook some short pasta, rice, barley, or other grain in salted water or broth and add it back to pot.”
If thickening the soup with pasta as it cooks: Cotter advises the following steps: “When you feel the ingredients are at the texture you want, with the desired flavor achieved, toss in a desired amount of pasta for 8-12 mins (less time if the pasta is small/fine) before you are ready to serve the soup. The pasta will cook in the soup, adding starch to the liquid, thus thickening it ever so slightly. Be warned, if the soup is a large batch, the pasta will continue to swell and absorb liquid, which could ultimately create more of a "stew" than a traditional soup.”
Adding bread is another way to thicken soup: “Throw some croutons on top and let the bread soak up some of that tasty broth,” Cotter says. “Ribollita is an Italian soup and translates to re-boiled. Leftover vegetable soup intentionally re-cooked with bread to thicken the soup and make it heartier.”
Method 6: Add Masa Harina
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About this method:
Masa harina is finely ground corn flour and when mixed with water, can be used to create a thicker consistency for soups and stews.
When to use this method:
Latin American soups such as posole or Tex-Mex dishes like chili.
What to do:
Cotter advises mixing masa with just enough water to form a paste. Cook the soup for 15 to 20 more minutes. “Masa will also add a great flavor as a bonus!” he says.
Method 7: Emulsifying Fat
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About this method:
Emulsifying fat into a pureed base can help to thicken soups and add mouthfeel and viscosity.
When to use this method:
Pureed vegetable soups. Sloan frequently uses this technique when making cold soups such as a cucumber-tomato gazpacho.
“I learned this technique many moons ago from Ashley Christensen when she made a melt-in-your-mouth tomato soup,” Sloan says. “She took the tomato base, pureed it under medium speed in a high powered blender and slowly streamed in high-quality extra virgin olive oil.”
What to do:
Slowly stream in olive oil while blending soups in a high-power blender or while using an immersion blender in a pot, until the desired consistency and viscosity is achieved.
Method 8: Reduce, Reduce, Reduce
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About this method:
Many soups rely on the reduction to thicken the consistency. “Reduction is based off the effect of evaporation and the resulting concentration of flavor,” Sloan explains.
When to use this method:
Any type of soup; it is particularly helpful when you don’t have ingredients on hand to use any of the other methods.
What to do:
Reduce your soup by simmering it until enough liquid has evaporated to achieve the desired thickness.
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