Even if you’re highly skilled in the kitchen, you might find yourself with a deflated cake or bone-dry brownies if you happen to be baking in Aspen, Colorado, for the first time. But why exactly does an oven at high altitude so often wreak havoc on whatever baked good is in it?
According to HuffPost, it all comes down to air pressure. The higher you are above sea level, the lower the air pressure is. This is mostly because there’s less air pressing down on that air from above, and it’s also farther from the gravitational forces on Earth’s surface. With less air pressure keeping liquid molecules in their liquid form, it takes less heat in order to vaporize them—in other words, boiling points are lower at higher altitudes.
“For every 500-foot increase in altitude, the boiling point of water drops by 0.9°F,” Dr. Craig F. Morris, director of the USDA ARS Western Wheat Quality Laboratory at Washington State University, told HuffPost.
Since liquids evaporate at lower temperatures, all the moisture that makes your signature chocolate cake so dense and delicious could disappear long before you’d normally take it out of the oven. To avoid this, you should bake certain goods at lower temperatures.
With less air pressure, gases expand faster, too—so anything that’s supposed to rise in the oven might end up collapsing before the inside is finished baking. Cutting down on leavening agents like yeast, baking powder, and baking soda can help prevent this. This also applies to bread dough left to rise before baking (otherwise known as proofing); its rapid expansion could negatively affect its flavor and texture, so you might need to adjust how much yeast you’re using.
If all the ways a recipe could go wrong at high altitudes—and all the experimentation needed to make sure it goes right—seem like a lot to keep track of, Betty Crocker has a handy chart with various types of baked goods and suggested modifications for them.