Reader Lilly writes:
What is the ineffable thing that gives marshmallows that almost chalky mouthfeel that they have? Egg whites? No. Sugar? No. Gelatin or vanilla? Couldn’t be. But that’s everything that’s in a marshmallow except for the water, so where does that texture come from?
The answer: corn starch. But that’s not an ingredient per se. Corn starch is actually a hidden component of powdered sugar which is what manufacturers use to “flour” marshmallows to keep them from sticking together. Corn starch is added to powdered sugar to absorb moisture and keep it from caking, usually in a proportion of about 3 percent. Not terribly much, but enough to give marshmallows that faintly cereal flavor and vaguely chalky texture.