About High-Altitude Baking

A lot of people forget that baking is a chemical reaction. Therefore, like all chemical reactions, the entire baking process is dependent on a number of factors like atmospheric pressure, climate, and elevation. The higher you climb (that is, the more elevation you gain above sea-level), the thinner the air, and the lower the atmospheric pressure. Almost all recipes are developed for use at sea level and, when used at or above 2,500 to 3,000 feet in elevation they will require adjustments for optimal results. Note that most changes start to occur at 2,500 to 3,000 ft above sea-level.

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:
  1. 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.

  2. 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!

  3. 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.
Again, this is just a short summary of the differences between sea-level baking and high-altitude baking. Bear in mind that each ingredient in a recipe is intended to provide a unique, necessary step in the baking's chemical process or the structure of the final product, so one set of adjustments does not fit all recipes.

For further in-depth reading about the changes in high-altitude baking and cooking, I recommend the following books and websites: