Instant Tapioca Preferable
The best option is to replace the arrowroot starch with an equal amount of instant tapioca, which often is sold as minute tapioca. This substitute holds up to long cooking times and works well in foods that are destined for the freezer. It also gives the filling in fruit pies a nice, glossy sheen.
Since tapioca doesn't fully dissolve when cooked, you may want to grind it into a fine powder before you add it to your recipe. Otherwise, you'll have little balls of tapioca in the finished dish. This won't affect flavor, but it will change the texture and appearance of your recipes slightly.
In a pinch, replace the arrowroot starch with an equal amount of cornstarch. It doesn't hold up as well in the freezer, breaks down in acidic dishes, and will give fruit jellies and fillings a slightly cloudy appearance. Expect some differences in the finished product if you decide to make this swap.
While both of these substitutes will get the job done, tapioca is the only gluten-free replacement for arrowroot powder. Of course, you still should check the packaging to make sure the tapioca was processed in a gluten-free facility.
What Arrowroot Powder Is
Arrowroot powder, also known as arrowroot flour or arrowroot starch, is derived from the roots of the tropical arrowroot plant, Maranta arundinacea. After it is harvested, it's dried and ground into the powder typically seen in stores.
It's used as a food thickener, much like cornstarch, but it has unique properties that make it well suited to certain cooking situations where cornstarch and other thickeners may not excel. When you add arrowroot to a recipe, it doesn't change the color of the ingredients or make the finished product look cloudy.
Because of this, it works well in jellies and fruit fillings, where you're trying to maintain that amazing color and shine. And since arrowroot doesn't fall apart when subjected to acidic ingredients, this is another reason that it's favored as a thickener for jellies and fruit fillings.
Arrowroot thickens at a low temperature, which can be handy in some applications, but it will lose its thickening power if it's exposed to high temperatures for a long period of time. Adding it towards the end of the cooking time can be a fix for this.
Despite its sensitivity to high temperatures, arrowroot stands up beautifully to freezing temperatures. So, if you're making something that you plan to freeze, arrowroot is an excellent thickener to use.
Other Uses For Arrowroot
In addition to being an excellent thickening agent, arrowroot has other uses. It's popular in vegan dishes because it can be used to bind ingredients together in much the same way eggs are used in nonvegan recipes. If you're making meatless burgers, for example, and don't want to use eggs, try adding some arrowroot to hold the ingredients together.
It also can be used in batters for frying foods. For example, if replacing meat in a stir fry recipe with something like tofu, coat your substitute protein with a combination of seasonings and arrowroot before frying to get a nice, crispy exterior.