General Knowledge
Why does the same recipe fail at high altitude?
- Water boils cooler, so food cooks slower
- Air is thinner to breathe
- Ovens are colder
The answer is Water boils cooler, so food cooks slower. Lower pressure means a lower boiling point - about 88 C in La Paz.
Because water boils cooler. Boiling happens when vapour pressure matches the air pressure pushing down, and at altitude there is less air - so water boils at 93 degrees in Denver and about 88 in La Paz. A pan of boiling water is simply not as hot, and anything cooked in it takes longer: dried beans at high altitude can refuse to soften at all.
Baking suffers differently. Lower pressure lets gas bubbles in a dough expand more, so cakes rise too fast and then collapse, and liquid evaporates quicker so things dry out. High-altitude recipes typically cut the raising agent and the sugar, add liquid, and raise the oven temperature - and the adjustments have to change again every few thousand feet.
The same physics runs the other way in a pressure cooker, which seals the pot so pressure builds and water boils at around 120 degrees, cooking several times faster. It is also why you cannot make a decent cup of tea on Everest, where water boils around 70 degrees, and why boiling water for a set number of minutes is a poor way to sterilise anything at altitude.