At altitudes above 3,000 feet, preparation of food may require changes in time, temperature or recipe. The reason is the lower atmospheric pressure due to a thinner blanket of air above. At sea level, the air presses on a square inch of surface with 14.7 pounds pressure; at 5,000 feet with 12.3 pounds pressure; and at 10,000 feet with only 10.2 pounds pressure — a decrease of about 1/2 pound per 1,000 feet. This decreased pressure affects food preparation in two ways:
Water and other liquids evaporate faster and boil at lower temperatures.
Leavening gases in breads and cakes expand more.
As atmospheric pressure decreases, water boils at lower temperatures. At sea level, water boils at 212 °F. With each 500-feet increase in elevation, the boiling point of water is lowered by just under 1 °F. At 7,500 feet, for example, water boils at about 198 °F. Because water boils at a lower temperature at higher elevations, foods that are prepared by boiling or simmering will cook at a lower temperature, and it will take longer to cook.
High altitude areas are also prone to low humidity, which can cause the moisture in foods to evaporate more quickly during cooking. Covering foods during cooking will help retain moisture.