Egg Boil Time by Altitude

Egg cooking time vs altitude

For every 300 m you climb, water's boiling point falls by roughly 1 °C, which works out to about T_boil ≈ 100 − altitude/300 °C. Heat moves into the egg more slowly once you're below 100 °C, so you have to give it longer in the water; cooler water means the proteins take more time to set. A soft-boiled egg runs about 4 min at sea level. Up in the Serra da Mantiqueira (~1,500 m, ~95 °C) you add roughly a minute. Get to Cusco (3,400 m, where water boils near 90 °C) and a properly hard-boiled egg stops being dependable unless you use a pressure cooker, which pushes the boiling point back up to ~120 °C and cancels the altitude out.

Applications

Cooking up in the Andes or the Himalaya, planning meals for a mountaineering trip or expedition, dialing in gourmet coffee at altitude (the extraction runs slower), timing pasta and rice in mountain cities, and keeping food safe in remote kitchens.

FAQ

Why doesn't a hotter flame fix it? Once water is boiling, its temperature is locked. Crank the flame and all you get is more steam, not hotter water. The food still cooks at T_boil.

Does a pressure cooker really help? It does. At 1 bar gauge the water hits ~120 °C no matter how high you are, so cooking times go back to normal, sometimes even quicker.

How accurate is the 1 °C / 300 m rule? It holds up well to about 3,000 m. Past that the Clausius-Clapeyron curve starts to bend, so reach for a thermometer when you need the real number.