Cooking at High Altitude
Cooking at high altitudes is different from cooking at sea level. Recipes that are otherwise reliable may not turn out properly when prepared at high altitudes. The reason for this has to do with differences in atmospheric pressures.
Higher Altitude, Lower Boiling Point
The higher the altitude, the lower the atmospheric pressure. Lower pressure, in turn, causes water to evaporate more quickly, and water actually boils at a lower temperature.
If it's hard to grasp the fact that boiling water is actually cooler at high altitudes than at sea level, that's because it's really, really weird. In theory, if you were high enough, a glass of water would boil at room temperature. So "boiling" — where we see the steam and rolling bubbles normally associated with the word, is really more a function of air pressure than temperature.
The effects are incremental, if not actually noticeable. In general, each 500-foot increase in elevation translates into a 1°F decrease in water's boiling temperature. So at 500 feet above sea level, water will boil at 211°F instead of 212°F. But the difference is so slight, you'll never notice it.
High Altitudes: 3,000 Feet and Higher
Where you will start to notice it is at elevations higher than about 3,000 feet. There, water will boil at around 207°F instead of 212°F. At 5,000 feet it will boil at around 203°F, and at 7,500 feet, it boils at 198°F. That's a significant enough difference where it will definitely affect how long it takes to cook something.
Remember, too, that at any given altitude, the boiling temperature of the water is as hot as water will get. You can't get it hotter by turning up the flame beneath the pot. So at 7,500 feet, you can't get water any hotter than 198°F.
What that means, then, is that you're going to have to cook foods a little bit longer than you would at sea level. Cooking pasta, for instance, which might take seven minutes at sea level, could take nine or 10 minutes at 3,000 feet.
Keep the Lid On
In addition to adjusting cooking times, you should also make sure that you keep a tight-fitting lid on the pot when you're cooking at high altitudes. This is standard procedure when preparing braised dishes, but it's a good rule to follow at high altitudes because water evaporates so much more quickly.
High Altitudes, Dry Air
Because the reduced atmospheric pressure of high altitudes affects the boiling point of water, it's moist-heat cooking techniques that are affected the most. Dry-heat cooking techniques like roasting or grilling are not affected in the same way because high altitudes don't alter the way air is heated. So a roasted chicken recipe shouldn't require any adjustment at higher elevations.
On the other hand, since water evaporates more quickly at high altitudes, meats cooked on the grill will tend to dry out more quickly than when cooked at sea level. Note that the temperature isn't affected, just the moisture content of the food. So a grilled steak might be drier at high altitude than at sea level — even if it's not overcooked temperature wise.
There's not much you can do about that, other than to make sure that you give grilled and roasted meats a chance to rest before serving them.
Cooking Eggs at High Altitudes
You'll also find that eggs will take a bit longer to cook at high altitudes because they naturally have a lot of water in them. But since fried eggs or scrambled eggs are cooked with dry heat rather than moist, take care that you don't compensate by using a hotter pan. That will just result in burnt eggs. When it comes to eggs, cook longer, not hotter.
Baking at High Altitudes
Another difference caused by the lower atmospheric pressure is that leavening agents such as yeast, baking powder or baking soda will have more rising power. That's because the thinner air offers less resistance to the gasses created by the leavening agent. Therefore, you should use less leavening (about 20 percent less at 5,000 feet) as your elevation increases.
And because of the faster evaporation described earlier, you may need to increase the amount of liquid in batters and doughs. You can do this by adding an extra egg or using extra-large eggs in place of large.
Microwaves and High Altitudes
You may also notice a difference in how microwave ovens work at higher altitudes. That's because microwaves cook by exciting the water molecules in food. Therefore, when using a microwave oven you'll likely want to allow extra cooking time as well.