When you add ground cinnamon to hot cocoa or oatmeal, they get thicker. Why does this happen?
We added 1 teaspoon of ground cinnamon to 1 quart of hot chocolate and experienced the same phenomenon: The spiced version was noticeably thicker than the cinnamon-free sample.
A little investigation revealed that more than half of cinnamon consists of carbohydrates known as polysaccharides, including pectin and cellulose, which can absorb water from liquid and swell. These compounds give cinnamon the power to thicken hot, fluid foods nearly as effectively as cornstarch. But that doesn’t mean cinnamon can serve as a spicy-tasting stand-in for starch. Just to see what would happen, we put the thickening power of the spice to the test by preparing two batches of pastry cream: one thickened with 3 tablespoons of cornstarch (per the recipe), the other with an equal amount of ground cinnamon (we’d never want to actually eat this one). While the batches turned out equally viscous, the cinnamon version had an unpleasant stretchy, ropy quality, thanks to the other carbohydrates present in the spice.
Bottom line: A teaspoon or so of ground cinnamon used in baking applications won’t noticeably affect texture. But if you want to avoid its thickening effect in warm beverages like hot chocolate or mulled cider, try steeping a cinnamon stick in your drink instead (polysaccharides don’t disperse from the whole spice).