Why do many foods have "High Altitude Cooking Instructions?"

★ wanayoo — archive 1999 http://howstuffworks.com/question63.htm

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Question

Why do many foods have "High Altitude Cooking Instructions"?

Answer

Most any packaged food that involves boiling (e.g. - boxed macaroni and cheese dinners) will have "high altitude" instructions. For example, I have here a box of Hamburger Helper that says:

High Altitude (3500-6500 ft): Decrease hot water to 3-3/4 cups. Increase simmer time to 17 minutes.

The reason foods have these instructions is because the boiling point of water changes with altitude. As you go higher, the boiling temperature decreases. At sealevel the boiling point of water is 212 degrees F (100 degrees C). As a general rule, the temperature decreases by 1 degree F for every 540 feet of altitude. On top of Pike's Peak, at 14,000 feet, the boiling point of water is 187 degrees F (86 degrees C). So pasta or potatoes cooked at sealevel are seeing 25 degrees more heat than pasta or potatoes cooked on Pike's Peak. The lower heat means a longer cooking time is needed.

Pressure cookers work in the opposite direction. A pressure cooker raises the pressure, so water boils at a higher temperature. A typical pressure cooker applies 15 pounds of pressure, so the boiling point of water rises to 250 degrees F (121 degrees C) at sealevel. The higher temperature means that foods take less time to cook.

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