Find Out How Heat Transfers in Brownies and Cakes

Pan of brownies with a red oven mitt
Thermal energy is one of the most important ingredients in the baking process. It’s what makes our brownies and cakes turn from a liquid to a solid.

How Does Heat Transfer?

Let’s talk about how thermal energy works! This is the energy that reflects the temperature difference between two systems (such as a cake and its baking pan) and causes molecules to move. It is transferred from molecule to molecule of a system (such as Betty Dream Cakes) until all molecules have the same energy. In other words, heat is moved around until the molecules have reached a constant temperature.

How Does Conduction Aid the Cooling Process?

When a cake (or brownie cake) is pulled from the oven, it is about 210 degrees Fahrenheit. To cool down, the energy inside the cake transfers to the baking pan and air molecules through the process of conduction. This process causes your cake to become cooler (by losing energy) while the surrounding air and baking pan gain energy and become warmer.

So what’s another example of conduction you might be familiar with? When an ice cube is held in your hand, it starts to melt. This is conduction at work since the heat from your hand is moving into the ice cube and causing it to melt!

How Do You Scientifically Cut the Perfect Piece?

The amount of time you let your brownies or cakes cool will ensure they don't crumble! When your baked goods are cooling, energy is transferred to the surrounding air. What you can’t see taking place is the atoms decreasing in motion and moving slower and closer together. When brownies and cakes are cooled, you're left with a tasty treat with science working behind the scenes! The atoms of your baked treats will essentially be vibrating back and forth, rather than flowing like they did when the batter was changing from a liquid to a solid. Now that the atoms are tightly packed, they can hold the shape of brownies or cakes! So when you cut it, your knife will be clean and your piece will be perfect!

How to Know When Brownies or Cakes Have Properly Cooled?

For this, we’ll rely on Fourier’s law of thermal conduction. This law calculates thermal conduction and the rate of heat transfer — in other words, the time to cool.

This isn’t the only law of science that your cakes or brownies use. They also incorporate the second law of thermodynamics — that heat always flows spontaneously from a hotter to a colder body (this could be a baking pan or the air around it). What does all this mean? Well, cakes and brownies just out of the oven will take about one hour to cool completely.

All icings have different melting points, depending on ingredients. That’s why you should wait for your baked treat to cool before icing.

Did You Know?
Did You Know?
  • Blowing on your food actually cools your food faster! Why is this? While blowing, you push away the steam cloud, which lowers the vapor pressure and allows more water to evaporate and cool faster.
  • The oldest ovens in the world are estimated to be 6,500 years old and found in Croatia.
  • In 1893, brownies were created at the Palmer House Hotel in Chicago's Loop.