Cupcakes bake in just 20 minutes because their small size allows heat to reach the center almost instantly.

The physics of baking is governed by thermal conductivity and the surface-area-to-volume ratio. In a standard cupcake tin, the batter is divided into small portions that maximize the surface area exposed to the oven's hot air. This allows heat to penetrate the batter much faster than in a large 9-inch round cake, which can take 35 to 50 minutes to bake thoroughly.According to food scientists like Harold McGee in 'On Food and Cooking,' heat moves through cake batter via conduction. In a large cake, the outer layers of cooked sponge act as an insulator, which significantly slows the transfer of thermal energy to the center. If the oven is too hot, the exterior will undergo the Maillard reaction and burn before the internal temperature reaches the necessary threshold for starch gelatinization.For most sponge-based recipes, the internal temperature must reach approximately 99°C (210°F) to ensure the structure is set. In a cupcake, the distance from the edge to the center is typically less than 3 centimeters. This short distance allows the center to reach the target temperature rapidly and evenly, resulting in a consistent crumb throughout the entire treat.Professional bakers often use the 'thermal spike' method to monitor this process, noting that smaller items lose moisture faster. Because the baking time is reduced to roughly 18 to 22 minutes, cupcakes retain more moisture than larger cakes that endure prolonged heat exposure. This efficiency is why industrial bakeries prefer smaller formats for high-volume production and consistent quality control.