Tapioca Harvested From Cassava

• Tapioca starch, also called tapioca flour, comes from the root of the cassava plant. The root is harvested, dried and then ground up to make starch. Tapioca is often used as a thickener, especially for fruit pies, because it turns clear when heated and gives a transparent shine. When used as a replacement for wheat flour in gluten-free baking, tapioca must be blended with other ingredients to provide sufficient structure. Tapioca starch also can inflate and aid in browning gluten-free baked goods. In fact, tapioca is so good at inflating dough that it must be watched carefully if used with yeast in a recipe so that the dough doesn't over-rise, risking collapse when baked.

Xanthan Gum Is Cultured

• Xanthan gum comes from bacteria called Xanthomonas Campestris. Xanthomonas is fed a glucose solution, after which the bacteria exude a sticky outer coating that's harvested as xanthan gum. Sometimes the glucose solution is made from wheat starch; at other times, it's cultured in high-fructose corn syrup. It's when corn syrup feeds the creation of xanthan gum that people with sensitivities can suffer allergic reactions because of gluten residue. It's also why xanthan gum sometimes gets a bad rap, even though the U.S. Food and Drug Administration has certified the additive as "generally accepted as safe" for human consumption. There's no way to know how xanthan gum was made unless the manufacturer chooses to say on the label, because an explanation isn't required.

Xanthan Gum 'Glues' Starches

• However it's cultured, xanthan gum most often is used as an emulsifier to help hold oil together with other ingredients, especially in sauces and salad dressings. In gluten-free baking, sticky xanthan gum serves to "glue" starches together in a matrix so that they can trap air in the same way that the sticky wheat protein, gluten, forms a network to trap carbon dioxide for leavening. That's why xanthan gum is deemed so important in gluten-free baking -- it does what gluten would do.

They Work Together

• Tapioca starch and xanthan gum generally work together, not in place of one another, when it comes to gluten-free baking. A typical substitute for wheat flour would include tapioca starch along with white or brown rice flour, xanthan gum and potato starch to create a gluten-free baking alternative.