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The air pressure is lower at higher altitudes; when you add extra flour to your baked goods, it prevents them from rising too quickly or too much.

ETA (about the water): Water boils at a lower temperature at higher altitudes, so the extra water called for in high-altitude baking is to compensate for all the water turning to steam faster than it would at sea level.

The air pressure is lower at higher altitudes; when you add extra flour to your baked goods, it prevents them from rising too quickly or too much.

The air pressure is lower at higher altitudes; when you add extra flour to your baked goods, it prevents them from rising too quickly or too much.

ETA (about the water): Water boils at a lower temperature at higher altitudes, so the extra water called for in high-altitude baking is to compensate for all the water turning to steam faster than it would at sea level.

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The air pressure is lower at higher altitudes; when you add extra flour to your baked goods, it prevents them from rising too quickly or too much.