How to boil water at high (and low) altitudes
We tend to think of the boiling point of water as a constant 212F (100C), but that temperature is only the amount of energy it takes to boil water at sea level. As elevation rises, the amount of air pressing down on the surface of the water decreases, and the less energy it takes to make the water boil, with the result that the water boils at a lower temperature.
The lower temperature of boiling water at high altitudes causes several changes in how food cooks:
• Boiling pasta, potatoes, beans, and other starchy foods takes about 10 percent longer for every 1,000 feet (305 m) of elevation.
• Braised meats are more succulent, because less moisture is squeezed from the coagulating proteins at a lower simmering temperature, but they may need slightly more time to cook.
For every thousand feet (305 m) of elevation, the boiling point reduces by about 2F (1C). Even a low-pressure weather front can lower the boiling point, or a high-pressure front could raise the boiling point by a degree or two.
The following chart shows how a change in altitude affects the boiling point of water and the cooking of common ingredients:
| Altitude Above Sea Level | Boiling Point | Vegetables (increase cooking time by) | Stewing and Braising (increase cooking time by) | Roasting (increase cooking temperature by) |
| 3,000 ft | 206°F | 20 to 30% | 30 minutes | 10 to 25°F |
| 5,000 ft | 202°F | 40 to 50% | 1 hour | 20 to 30°F |
| 7,000 ft+ | 198°F | 60 to 70% | 2 to 3 hours | 30 to 50°F |
If you go in the opposite direction, below sea level, there is more air sitting on the surface of the water and the boiling point goes up. Since there is not much dry land that lies below sea level, increasing the boiling point of water by increasing atmospheric pressure most often happens artificially in a pressure cooker. Pressure cookers speed up cooking by trapping the steam escaping from boiling water, thereby building up pressure on the surface, and raising the boiling point.
In a pressure cooker, the combination of the increased temperature and air pressure forces heat into ingredients faster, thereby reducing cooking times by as much as 70 percent. Soaked dried beans can take as little as 10 minutes to cook through in a pressure cooker. A pot roast that would braise for 3 hours using conventional cooking methods will take less than an hour in a pressure cooker. Because there is less evaporation in pressure cooking, the amount of liquid used for a soup, stews, or braised meat should be reduced by about 60 percent.
