Why does coffee stain cups?
Show answer & explanation
Answer: Tannins bond to cup surface
Tannins bond to cup surface ✓ — Correct! Coffee contains tannins—organic compounds that easily bind to porous surfaces like ceramic, plastic, and teeth enamel. These molecules create brown stains that build up over time. Hot water makes tannins bind stronger. Baking soda removes stains by breaking these chemical bonds!
Heat bakes coffee into ceramic — Wrong. Heat doesn't 'bake' coffee into cups. Staining happens even with cold coffee—it's chemical bonding of tannin molecules to the surface.
Sugar caramelizes on sides — Wrong. Most coffee has little to no sugar unless you add it. Stains come from tannins (natural plant compounds), not sugar caramelization.