How Starches Gel

• Uncooked starches such as tapioca powder have only a minimal ability to thicken liquids by absorbing water. This is fine if you want to make paste, but a simple mixture of starch and cold liquids is grainy and unpleasant on the tongue. If you take that same mixture of starch and liquid and add heat, the starch's structure changes. Its molecules open up and unwind, dispersing through the liquid and forming loose bonds like a three-dimensional fish net. At temperatures between 126 and 150 degrees Fahrenheit, the elongated mesh of starch molecules becomes firm and traps the liquid, creating a gel.

Tapioca and Pearling

• Tapioca is made from the roots of manioc or cassava, a starchy tuber that's a dietary staple in tropical countries, as potatoes and rice are elsewhere. The refined tapioca starch is an effective thickener, like cornstarch or arrowroot, and produces a nicely clear sauce. Unfortunately tapioca powder has a slightly stringy texture that many diners find unpleasant, so it's usually rolled into small granules or "pearls." These provide thickening, but also become an element in the finished dish.

Using Tapioca

• To prepare your tapioca, stir the pearls into a cold liquid and then heat it gently. For example, you'd make tapioca pudding by stirring the pearls into sweetened milk with a dash of vanilla or other flavorings. If you don't want the thickening effect but just the finished pearls, cook them separately in a suitable liquid such as tea or sweetened water. Drain and rinse the cooked pearls and add them to your iced tea or other beverage.

"Instant" Tapioca

• Instant tapioca is rather different from the standard variety. Like parboiled rice or quick-mixing gravy flour, these granules are heated to the point of becoming a gel and then dehydrated again. When they're mixed with a heated liquid, they quickly absorb the moisture they need to rehydrate and create fully gelled pearls. Instant tapioca doesn't have quite the texture of fully cooked conventional tapioca and isn't as strong a thickener, but it's quick and convenient for when time is a consideration.