Using a thickening agent can instantly add a creamy and flavorful texture to any savory or sweet recipe. Here’s a helpful guide to understanding the process of how cooking starches and gums to a gel-like consistency helps to thicken sauces, stews, and fillings.
Plants naturally contain starches as an energy source, which can be extracted and used for adding thickness to food. Starch gelatinization is vital for developing thicker sauces as the properties of the ingredients change when heated.
There are many types of thickening agents to choose from. Examples of plants that contain starches for cooking applications include; corn, rice, wheat, barley, spelt, oat, beans, peas, potatoes, tapioca, arrowroot, green bananas, plantains, gums, and pectin. Let’s take a closer look at the science behind ways to create a delicious sauce using a thickening agent, and the most common types to have stocked in the pantry.
What is a Thickening Agent?
Starch-based thickening agents are polysaccharides. Large molecular weight carbohydrates which interact and form gels or thickened dispersions when in contact with water. Amylose and Amylopectin are two major polysaccharides in starches that are responsible for thickening foods.
The structures of these polysaccharides are dependent on the plant source. The ratio of amylose to amylopectin impacts their thickening properties. In general, the thickening power, clarity, and stickiness of a starch paste are most significant with cereal grains, roots and then tubers like wheat, corn, arrowroot, and potatoes.
How A Thickening Agent Works
By applying heat to the starch and water mixture, the viscosity increases due to initial swelling and dissolution.
Two stages of swelling for starches to thicken
- Gelatinization: Heat irreversibly disrupts the semi-crystalline structure of the uncooked starch granule. This process allows amylose and amylopectin starch granules to solubilize and absorb the water and begin swelling. The temperature needed for gelatinization happens over a range and is starch dependent.
- Pasting: To achieve maximum thickness, the second stage requires the starch slurry to be heated a few degrees higher than the gelatinization temperature. Agitation is also needed by whisking the sauce to prevent lumping. This process allows the starches to swell independently from each other while the heat reaches the endpoint cooking temperature for the greatest thickness capability of a sauce.
How to Tell When Thickening is Complete
- Taste & Consistency: Once the sauce has thickened, there should be no raw flour or starchy taste. The product should have a smooth texture and consistency that can coat the back of a spoon. This quick test indicates that it will cling to food when poured or mixed.
Starches Can Breakdown
- Breakdown: If you hold the starch paste too long or too high at its endpoint temperature, you will notice the viscosity start to thin, this is called breakdown or shear thinning. This is why some starches like arrowroot or cornstarch should not be reheated.
- A general rule of thumb to substitute starches:
- 2 tablespoons wheat flour = 1 tablespoon cornstarch = 1 tablespoon tapioca = 3 1/2 teaspoons arrowroot = 1 1/2 tsp. potato starch (Source: Fine Cooking) Depending on the desired thickness of the product and use (sauce, filling, or baked), these amounts may vary.
Common Types of Thickening Agents:
Here is a list of the most common starch and gum food thickeners.
Wheat flour is the thickening agent to make a roux. A roux is a mixture of flour and fat and is a classic way to thicken soups, gravies, and sauces like bechamel or stews like gumbo. Equal parts of wheat flour and typically butter are cooked in a heated vessel, forming different colored pastes depending on use.
Roux made from wheat flour are classified into white, blond and brown varieties. The cooking allows the fat to effectively coat the flour to prevent clumping, once whisked with a liquid. To prevent a lumpy sauce either add cool roux to a hot stock, or cool stock to a hot roux.
The corn endosperm is ground, washed, dried to a fine powder. This gluten-free thickening agent can be used to give sauces more viscosity and sheen rapidly. Cornstarch is often used in Chinese cooking for stir-fry sauce. It has twice the amount of thickening ability compared to flour, but if heated too long can break down and lose some of its consistency.
The key to incorporating cornstarch into hot or cold liquids is to make a slurry. Typically 2 parts cold water is mixed with 1 part cornstarch until an opaque mixed is formed. For example, 1 tablespoon of cornstarch with 2 tablespoons water to thicken about 2 cups of hot liquid. More slurry can be added for a thicken sauce.
Arrowroot starch is extracted from the tubers of the tropical plant, Maranata arundinacea. A very fine white powder with similar thickening to cornstarch. Arrowroot powder is neutral in taste and keeps sauces clear.
A slurry should be made before adding, 2 parts room temperature water to 1 part arrowroot powder into a hot liquid. Do not reheat sauces made with arrowroot. An excellent option for grain-free, gluten-free diets, and very popular in Whole30 and Paleo lifestyles.
Tapioca starch is made from the South American cassava plant or yuca. The fine white powder has a slightly sweet flavor but does not add a noticeable flavor. It’s most often used for fruit pie fillings because it thickens quickly and reheats and freezes well. It does not work as well for sauces like gravies that requires a lot of stirring.
Advantages of using tapioca starch are that it does not discolor when cooking, is gluten-free, and does not separate or clump when refrigerated or frozen. When replacing cornstarch, it requires 2 times as much. For example, use 2 tablespoons per 1 tablespoon of cornstarch.
Xanthan Gum is a microbial polysaccharide made from fermenting sugar with a bacteria called Xanthomonas campestris, which creates a gel that is dried and milled into a powder. The neutral-tasting gum acts as a powerful thickening, emulsifying, and stabilizing agent. It’s most often used for thickening and stabilizing gravies, sauces, dressings and non-dairy milk and ice creams as it adds a creaminess and richness to those recipes.
It’s also a great binder for gluten-free baking because it mimics the gluten function in a dough to give elasticity and viscosity. Xanthan Gum is unique in that it can thicken at a range of temperatures very quickly, so it does not need to be heated. Only a very small amount is needed to thicken a mixture, about 0.1% to 1% weight ratio.