Ask The Expert: Substituting Starch
GFM’s special diet chef answers your questions about allergy-friendly baking.
[Updated July 27, 2017]
Q: Are tapioca starch and potato starch interchangeable?
A: Yes, they are. But potato starch is a bit heavier than tapioca starch. So a recipe with a gluten-free flour blend that’s more than a quarter tapioca starch will be a little denser if you use potato starch instead. To alleviate this, replace 25 percent of the tapioca starch with potato starch and then increase another flour in your recipe by ¼ cup for every two cups of flour blend.
A word of caution: Don’t confuse potato starch with potato flour. They are two different products. Potato flour is extremely absorbent, not light and fluffy like potato starch. Potato flour is not interchangeable with tapioca starch or with potato starch.
Bread Recipe Revision
Q: I’m allergic to wheat and oats, among other things. Recently, I learned I can no longer eat potatoes and baker's yeast. I’ve always made my own bread using potato starch and yeast. I don't know what to do now. What are good substitutes for these key ingredients?
A: Since you’re already making your own bread, you only have to improvise a little bit to address the new food allergies. Start with the bread recipe that worked for you before. Omit the potato starch and replace it with tapioca starch or arrowroot. If you happen to be using mashed potato flakes, replace them with quinoa flakes in the same amount. Instead of using baker’s yeast as a leavening agent, try adding 1 tablespoon of baking powder. Mix it with your recipe's other dry ingredients.