The Physics of Boiling Water at High Altitudes
The boiling point of water is universally taught as 212°F (100°C). However, this rule only applies at exactly sea level under standard atmospheric pressure (1 atm). As you ascend in altitude, the atmospheric pressure pushing down on the surface of the water decreases. With less resistance from the atmosphere, water molecules require less thermal energy to escape the liquid state and become a gas. Consequently, the boiling point of water drops significantly at higher elevations.
Impact on Cooking and Baking
This physical phenomenon has profound implications for cooking. Because water cannot exceed its boiling point (any additional heat simply turns more water into steam, rather than raising the temperature), foods cooked in boiling water at high altitudes are subjected to lower temperatures. This means that a pot of boiling water in Denver, Colorado (elevation 5,280 ft) is significantly cooler than a pot of boiling water in Miami, Florida (sea level). As a result, pasta, rice, beans, and boiled eggs will take much longer to cook thoroughly at high altitudes.
The Formula
For a quick approximation, the boiling point of water drops by roughly 1°F for every 500 feet of elevation gain above sea level (or roughly 1°C per 285 meters).
Boiling Point (°F) ≈ 212 - (Altitude / 500)
(Note: While this linear approximation is highly accurate for general culinary purposes, true boiling point calculations rely on the Clausius-Clapeyron relation and local barometric pressure, which fluctuates with weather patterns.)
Adjusting Recipes for Altitude
When boiling foods at altitudes above 3,000 feet, you must increase cooking times. For baking, the lower pressure means leavening agents (like yeast or baking powder) expand much faster, which can cause cakes to rise rapidly and then collapse. High-altitude baking adjustments often involve reducing leavening agents, increasing oven temperature slightly, and adding more liquid to compensate for faster evaporation.