You will need an effective thickener if you are making a pie filling, a gravy or a sauce. Corn starch is the go-to thickening agent for many cooks and is both affordable and easy to find. If you need a thickener and find that your corn starch canister is empty, there is no need to panic. Try one of the corn starch substitutes below.
Your best bet: Tapioca
Tapioca is made from dried and ground cassava root. It is made into a fine flour that is very much like corn starch in texture. Like corn starch, it offers the ability to thicken liquids without affecting flavor. Some tapioca fans believe that it is actually better than corn starch since it does not mask the flavor, which corn starch can do despite the fact that its flavor is neutral.
Use tapioca in exactly the same way that you would use corn starch. Make a slurry by mixing it with water and add it to whatever you want to thicken. Note that its thickening power is a little less than that of corn starch, which means that you will want to use twice the amount of it that your recipe requires for corn starch.
A decent second choice: Arrowroot
Like tapioca, arrowroot is also made from tubers. The arrowroot tubers come from the arrowroot plant, which is a member of the Marantaceae family. It can provide a neutral flavor and good thickening just like corn starch and tapioca. Arrowroot has a number of advantages over corn starch including the fact that it can stand up to acids without breaking down, which something that corn starch cannot do. In addition, it can also be frozen and thawed without losing its properties.
Use arrowroot as a corn starch substitute at a 1:1 ratio. Use the same amount that your recipe requires for corn starch and mix it with water to make a slurry. Note that arrowroot will not be effective in a liquid that contains dairy and will break down if you overheat it. You will want to remove the dish to which it has been added from the heat as soon as it starts to thicken.
In a pinch: Flour
Flour is made from wheat rather than from corn. It contains protein, fats and sugars along with its starch. Because of the additional content, it does not have a neutral flavor. It is best when used in dishes with a strong flavor that will mask its presence. Note also that because flour is not a pure starch, you need more of it to thicken a given amount of liquid when compared to the much purer corn starch.
Liquids thickened with flour are not clear and glossy the way they are with the thickeners above; sauces will be cloudy with a matte surface, which makes flour a better option for dishes with dairy ingredients. Flour can stand up to both acids and high temperatures.
To use flour as a substitute for corn starch, use twice the amount that your recipe requires for corn starch. Make a slurry as with the other thickeners above and add it to your dish.
Potato starch is starch derived from the potato tuber and it works like all of the thickeners above, just mix with water to make a slurry. Like tapioca and arrowroot, it can thicken at a lower temperature so there is no need to boil it.