104. Why do high altitude places have different cooking temperatures than sea-level places?
The air pressure is lower at high altitudes than it is near sea level because there is less atmosphere overhead to support. This decreased air pressure affects the way water boils. Molecules can always evaporate from the surface of a pot of water, even when that water is cold, but above a certain temperature, water molecules can begin to evaporate from the interior of the water as steam, the gaseous form of water, in a process we call boiling. The temperature at which boiling occurs depends on the ambient air pressure because it can only proceed when there is enough pressure inside the steam bubbles to make them grow larger. At high altitudes, the lower air pressure makes it easier for these steam bubbles to form and grow, so they occur at lower temperatures. That's why water boils at a lower temperature at high altitudes. Once water reaches its boiling temperature, any heat that you add to it tends to cause the water molecules to boil away rather than to make the water hotter—so it's hard to heat water-containing food hotter than the boiling temperature of water. Since food needs high temperatures to cook, they don't cook as easily at high altitude where the low boiling temperature of water tends to keep the food from getting very hot.