Onion skins are usually treated as packaging supplied by nature: useful until the bulb reaches the chopping board, then discarded. Chemically, though, those papery layers are unusually concentrated plant material, rich in fiber and phenolic compounds such as quercetin. That makes them an interesting candidate for “upcycling” into flour-based foods—provided the resulting food still behaves and tastes like food.

A 2020 study in Scientific Reports tested that idea in pizza bases. The researchers cleaned red-onion skins, freeze-dried them, ground them into a powder, and used it to replace 2%, 3.5%, or 5% of refined wheat flour. They then measured the dough’s mechanical behavior, the baked base’s texture and color, antioxidant-related chemistry, sensory acceptance, and microbial growth during storage.