As altitude increases, air pressure decreases. This has several implications for cookery:
- water boils at lower temperatures
- water and other liquids evaporate faster
- gases which raise or "leaven" baked goods expand faster
In baking at altitudes of 5,000 feet (1,500 meters) or higher, more rapid expansion of your leavening agent will stretch the little bubbles which give your cake or bread its "cell structure". Then, the evaporation of water will raise the concentration of sugar and fats, which will weaken the "cell structure" further, causing it to fall. Thus, your muffins blow up and then crater.
Thus, for baking at high altitude you must:
For 5,000 feet (Denver or Albuquerque) the general rule of thumb for recipe adjustments: reduce your baking powder or soda by 1/8 teaspoon per teaspoon, reduce sugar by 1 or 2 tablespoons per cup, and increase liquids 2 or 3 tablespoons per cup, and increase your baking temperature by 25º F.
While pure water in a smooth container can be briefly "superheated" --brought to a temperature higher than the boiling point-- once gas bubbles form and boiling begins, the escaping gases remove excess heat and keep the boiling water at a constant temperature. That temperature varies with altitude as follows:
Altitude Water Boiling Point
0 (sea level) 212ºF (100ºC)
000 feet (305 meters) 210ºF (98.9ºC)
2000 feet (610 meters) 208ºF (97.8ºC)
3000 feet (914 meters) 206.4ºF (96.9ºC)
4000 feet (1219 meters) 204.5ºF (95.8ºC)
5000 feet (1524 meters) 202.75ºF (94.9ºC)
8000 feet (2438 meters) 197.5ºF (91.9ºC)
This means that your sea-level "three-minute egg" will need longer than 3 minutes to attain the desired consistency in Denver, Colorado (5,280 feet/ 1,609 meters), or Santa Fe, New Mexico (7,000 feet/ 2,100 meters) and certainly in La Paz, Bolivia (13,500 feet/ 4,114 meters). On Mount Everest (9,500 meters) water boils at 167º F (75º C) . Anyone who wants to boil eggs on the summit of Everest had better check their oxygen levels.
If you brought the family's antique double boiler with you when you moved to the mountains from the coast, intending to make the traditional family pudding, or confections like ebbixx's Chocolate Hazelnut Cookies ... send it back home and prepare to learn a new skill.
At about 5,000 feet, and definitely above 7,000, the low boiling point of water makes the double boiler slow. We're talking molasses in January. Starch in pudding will not gel, egg yolk based sauces like Hollandaise refuse to stiffen. Use direct heat: for Hollandaise, for example, put a steel bowl directly on the stove burner on low, and stir and rotate the bowl constantly to avoid scorching. For melting chocolate or butter, nothing beats a microwave, anyway.
While boiling takes longer at high altitude, deep-fat frying still works at the same rate. If, however, we are relying on steam to cook the inside of something in the deep fryer, the temperature recommended in a sea-level recipe may leave food undercooked on the inside, even when it's extra-crispy on the outside.
To restore balance and fatty equity, frying temperature has to be lowered about 3 degrees F for every 1000 feet of altitude.
- Rombauer et al, Joy of Cooking at 145 and 692 (5th Ed. 1975)