Repeatedly Reheating Coffee Might Upset Your Stomach
Reheating brewed coffee several times shifts its chemistry, increasing bitterness and acidity as chlorogenic acids break down. For many, a single reheat is fine, but daily multiple reheats can aggravate reflux or dyspepsia. To keep your gut happier: drink fresh, avoid reheating more than once, use a tumbler to minimize heat cycling, and consider milder roasts or cold brew.