Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent six days a week. Who doesn’t love a brownie? It’s the ultimate comfort food—beloved around the world and even beyond it. Astronauts aboard the International Space Station have brownies on their menu too . But what makes a perfect brownie? That depends on who you ask. Some like a light, cake-like crumb. Others want a dense, fudgy center or a chewy bite.  To tailor your brownies to your taste, you need to understand the science behind them. “Each ingredient has a specific role, and the ratios between them determine whether the brownie turns out fudgy, cakey, or chewy,” explains Dr. Lesa Tran , a chemistry professor at Rice University.  What each ingredient really does Flour Flour is the backbone of your brownie. When mixed with water, its proteins (gliadin and glutenin) link up to form gluten, a network that gives structure, explains Tran.…