What follows is a quick summary of what happens when altitude begins to affect cooking and baking. Most of this information was taken from Epicurious.com's High-Altitude Baking Guide:
- Water boils at lower temperatures.
That is, the higher the elevation, the lower the boiling point of water. For instance, water boils at 212 °F (100 °C) at sea-level, but boils at 203.2 °F (95 °C) at 5,000 ft. When water boils at lower temperatures, it takes longer for foods to cook in water since the water isn't as hot when it's boiling. This also means that it takes longer to cook foods that are in or over that liquid: batters will often crust over on top or on the sides (where they are touching the metal pan) before the interior gets hot enough to bake through.
- Moisture evaporates faster in higher elevations.
When moisture evaporates faster, the ratio of liquids to solids in your recipes change and can potentially weaken the overall structure of whatever you're baking. Baked goods also dry out and go stale at a faster rate, so invest in some good tupperware!
- Leavening gases like air, carbon dioxide, and water vapor expand faster in higher elevations.
Baking powder and baking soda provide the principal leaveners for most baked goods, creating air, steam, and carbon dioxide gas in mixture/batter. When these leavening gases expand quickly, cakes rise far too quickly and proceed to sink in the oven or during the cooling process.
For further in-depth reading about the changes in high-altitude baking and cooking, I recommend the following books and websites:
- Pie in the Sky: Successful Baking at High Altitudes by Susan Purdy
- How Baking Works: Exploring the Fundamentals of Baking Science by Paula I. Figoni
- Epicurious's High-Altitude Baking Guide by Susan Purdy
- High-Altitude Baking by the King Arthur Flour Company