February/March 2015

Getting to Know: Thickeners

Achieving the right consistency in a sauce, custard, pie, or jam takes a little knowledge . . . and some help from these common thickeners.

All-Purpose Flour

Flour can thicken a substance alone, as part of a slurry, or in conjunction with a fat. In a roux, a mixture of flour and fat is cooked to eliminate the raw flour flavor before introducing liquid. In a beurre manié, a paste of flour and softened butter is added to a soup or sauce to finish it. In either case, combine them with liquid gradually and whisk them in well before the mixture boils, when the flour’s starches cause the mixture to thicken.


Because cornstarch is a pure starch, it is a more effective thickener than flour (which is only 75 percent starch). But cornstarch-thickened sauces break down more quickly than flour-thickened ones, so be sure to follow the cooking times for recipes thickened with cornstarch and to reduce the heat once the dish has thickened. Cornstarch is the go-to thickener for stir-fries; first mix it with cold liquid to form a slurry before adding the thickener to hot liquids to prevent clumping.

Heavy Cream

Just a few tablespoons of heavy cream, which is 38 percent fat, can add distinct richness to sauces. Reducing heavy cream by boiling increases the concentration of fat globules to create the texture of a starch-thickened sauce. Cream was the only thickener we needed in our recipe for Creamed Kale with Chestnuts.


The ultimate sauce finisher, butter contributes a glossy sheen, richness, flavor, and thickening to pan sauces (and to custards like lemon curd). But in order to achieve the right body, it’s important to add butter off the heat. Because butter is an emulsion that can be broken by high temperatures, at around 160 degrees your nicely thickened sauce will lose its body.

Egg Yolks

Rich custards like crème anglaise and lemon curd rely on egg yolks to achieve a creamy texture. Temperature is key to their thickening ability: If the yolks get too hot, their proteins coagulate and lose water, leaving you with a curdled, watery sauce. The takeaway? Don’t boil custards thickened with egg yolks; you’ll know that your custard has thickened when a spatula leaves a clear trail in the pan.


Commercial pectin begins with apple or citrus extract and is chemically processed to produce a dry, powdered substance. Unlike gelatin, regular pectin requires the presence of sugar and acid in order to gel (that’s why there’s special pectin for low-sugar jams and preserves). We use pectin to achieve strength without rubberiness in our Raspberry Chiffon Pie.

Potato Starch

Potato starch begins to thicken liquid before it reaches a simmer, while other starches must simmer for several minutes first. But the large starch granules can cause finished sauces to appear grainy, and it tends to thin out after prolonged cooking. For best results, add potato starch later in the cooking process, and take your sauce or soup off the heat as soon as it thickens.


Tapioca starch comes from the tropical root vegetable cassava, also called manioc or yuca. This neutral-tasting thickener can be an asset in some fruit pies and in the slow cooker. For our Slow-Cooker Hearty Beef Stew, Minute tapioca—our favorite brand—was able to maintain its power over long hours in the slow cooker (unlike flour and cornstarch).


We use this pure protein in a variety of ways in the test kitchen: to thicken soups and braises, to stabilize whipped cream, and to shore up fruit pies like our Icebox Strawberry Pie. Gelatin is sold in thin sheets and powdered. Both forms must be hydrated in cold water before being melted and incorporated. Basically, gelatin is used to turn liquids into solids (think your grandmother’s green Jell-O fruit salad).


Arrowroot has almost twice the thickening power of flour. Unlike flour and cornstarch, it doesn’t become cloudy as it thickens, so it leaves pie fillings and sauces clear. We’ve found arrowroot to have a slimy quality in recipes with dairy, so we don’t recommend its use in puddings and custards. Arrowroot is almost as powerful as cornstarch; use 1 1/2 teaspoons of arrowroot for every 1 teaspoon of cornstarch.


Okra has a long growing season in the southern United States. Elsewhere you’re likely to find it frozen (we couldn’t tell the difference between fresh and frozen when cooked). The long, green, tapered pods have a mild vegetable flavor that gets lost in spicy dishes; they’re used for their sticky, mucilaginous insides. Once okra is sliced and its liquid is released, it becomes a thickener in Louisiana dishes like gumbo and étouffée.


This complex carbohydrate is made from red algae, a form of seaweed. Available in flakes or powdered form, agar-agar has a thickening power similar to gelatin and is often used as a vegan alternative. The thickening strength can vary from brand to brand, but we generally found 3/4 teaspoon of agar-agar flakes comparable to 1 teaspoon of gelatin when used to thicken 1 cup of liquid. Unlike gelatin, however, the agar-agar flakes need to soak in water for 10 minutes before the mixture is boiled for 10 minutes longer.