Most sauces use starch as a thickening agent to thicken and reduce viscosity. The most common starches are cornstarch and wheat starch, usually in the form of flour. How does this thickening process between starch and sauce work?
Understanding the Sauce Before the Starch
Sauces come in an infinite variety of flavors and types. The basic dessert sauce is a mixture of a liquid, a sweetener, a fat, and a starch. Dinner sauces are similarly constructed without the sweetener. The sweetener can be sugar, brown sugar, honey, or more. The fat gives a pleasing “mouth feel” to the sauce, usually with butter or cream. The starch can be either corn or wheat flour. Flavors are added from spices and extracts to chocolate.
Most sauces will be runny and almost unpleasant without some form of thickening agent, though not every sauce is made with starch. With enough sugar and cooking, the starch is often omitted. Fruit sauces, for example, are often made without starch. They rely on the pectin and solids in the fruit for thickening. Some sauces are thickened with eggs.
How Starch Works as a Thickening Agent
Starches are used as thickening agents for sauces, soups, and pie fillings. The thickening doesn’t occur until the starch gelatinizes. Gelatinization is the process whereby the starch particles absorb moisture, expand, and become firm.
This process starts at 140 degrees and is complete when the sauce becomes bubbly. If you quit cooking the sauce before gelatinization is complete, the sauce will not be as thick as it could be. The sauce will thicken further as it cools.
Cornstarch in particular sets up almost like gelatin, making it especially valuable for pie fillings. Sauces made with cornstarch are clearer and more translucent than those made with wheat flour since the wheat flour is comprised of more than starch.
How to Mix the Starch into Your Sauce
The starch must be evenly distributed in the sauce to avoid lumps. There are two basic ways to do this. In most recipes calling for butter, the starch is mixed with the melted butter to form a paste and then the liquid is added all at once and stirred well for distribution.
In other recipes, the sugar and starch are well-mixed in the pan before the liquid is added. In either method, frequent stirring is required. A bell-shaped whisk is the preferred way to stir and is an indispensable tool for making sauces.
Practice with Thickening Agents and Sauces
You do not need a recipe to make a sauce. You simply need an idea of a flavor, some liquid, a sweetener, some fat, and a thickening agent to mix together until you get it just right. With just a little practice, you can make sauces without following a recipe. But for now, why don’t you start out with these recipes just to make sure you’ve got it down.
- Hot Caramel Sauce: Notice that this sweet dessert sauce relies on cornstarch as the thickening agent and doesn’t completely thicken until it comes to a complete boil and then cools down.
- Lemon and Herb Sauce: Notice that this sauce relies on flour as the thickening agent, making a roux with the flour and butter in the pan before mixing in all the other ingredients.
- Homemade Marinara Sauce: Notice this tomato sauce uses neither flour nor cornstarch as a thickening agent, but the tomatoes and heat. You cook the sauce on the stove for ten minutes for it to fully thicken.
(Updated from May 12, 2014)