Does food cook more slowly at altitude?
Is this a deep truth or the height of foolishness? The answer may not have much practical import, unless you have a passion for scaling peaks and whipping up gourmet meals — and even then, only if you combine the two — but there’s nothing wrong with a bit of pure knowledge. Altitude can slow cooking, depending on what you cook.
It’s not really height but pressure that is responsible. We all know that atmospheric pressure drops the higher you go. That’s what makes your ears pops as you climb or descend, as the pressure inside your ears equalizes with the changing pressure outside.
Now pressure has a lot to say, along with temperature, about the way substances behave, and we are particularly interested in water. We’re used to idea that as temperature rises ice melts into water and then boils into steam. What you may not know is that this is just a tiny slice of the whole picture. By varying both temperature and pressure you can create steam, liquid water, ice, ice, ice or ice to name just a few — physicists having discovered quite a few different kinds of ice, presumably in a quest for the perfect scotch on the rocks. At sea level water boils at 100 degrees Celsius, or very close to it. But rise to the altitude of Mt Cook and water now boils at something like 86 degrees Celsius and at the summit of Mt Everest a miserable 70 degrees Celsius.
But doesn’t that mean that water boils faster, if anything? Well, yes, but it doesn’t get as hot. Because water just can’t reach as high a temperature — it boils off into steam before it can — cooking is slowed just as if you had turned the heat down. A boiled egg takes longer to cook and anything relying on the boiling point of water in its cooking is affected.
So high altitude can slow cooking. If you want to make sure your alpine cookery doesn’t turn to custard (or, in the case of custard, that it does), just take your time.