Diffusion. Phases. Temperature. And the perfect molten chocolate cake.
1-Minute NomNom
Baking cooks food by a process known as heat diffusion. Baking the perfect chocolate lava cake is all about controlling the temperature and timing of that process.
Most lava cakes today are made from recipes where the chocolate cake is “half-baked”. The baking is stopped before the heat diffusion process is complete. As a result, the inside of the cake is not fully cooked, giving us our yummy oozy lava center.
molten chocolate cakes ready to be baked
Sounds simple right? The science is simple too.
When the chocolate cake batter is first put into the oven, the particles in the exterior of the cake mix heat up first through radiant heat and convection in the baking over. These particles in turn heat up the cooler particles around them i.e. conduction (read all about different types of heat transfer in the 1-Minute Marvels “Pleased to heat you!“).
Over time, all the particles inside the chocolate cake are cooked by this outside-in process. But if we stop this part way, only half of the chocolate cake will be cooked. The center remains liquid, and giving us half-baked but still lava-able yumminess.
after baking, or half-baked, molten chocolate lava cake
We can calculate how much time is needed to get the liquid center. According to Harvard’s Science and Cooking course, the equation is T(t) = (Tinitial − Texternal)e (−t /τ ) + Texternal . Those of you who are interested can find out more at this New York Times/Harvard document. The rest of us will just have our lava cake and eat it too.
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