Reader Mark asks:
Living in Denver, Colorado, which is known (among other things) as the Mile-High City, I know all about falling cakes. Can you comment on how altitude affects the baking process and what adjustments need to be made to recipes?
Great idea, Mark, and well-timed. What happened to me with my Japanese cheesecake is in fact very similar to what happens to most bakers at high altitudes: they get a whole lot of leavening action, which weakens their cake’s (or muffin’s or whatever’s) structure and the thing falls.
Why is that more likely to happen at a high altitude? I think of it this way: the atmosphere on planet Earth has weight. The more atmosphere you happen to be under, the more it presses down on you, i.e. the more pressure it exerts per square inch. It’s sort of like a swimming pool, the deeper you dive, the more the weight of the water above you presses in on your eardrums.
Climb up a mountain and there’s less atmosphere above pressing down, not only on you, but on the bubbles inside your baking cake. Which means those bubbles expand to larger volumes than they would at a lower altitude. But there’s another complicating factor as well. Due to lower pressure, water boils at a lower temperature. That means you start getting steam in your batter sooner, at a point where the egg proteins may not yet have firmed and are ready to hold in — i.e. capture — the rise. The result being that steam and gas simply bubble out of the liquid batter.
The solution to overactive leavening? Obviously, less leavening. At 5,000 feet above sea level, when a recipe calls for an egg foam at stiff peaks, whip to soft peaks. At 7,000 feet, whip to very soft peaks. Likewise with chemical leavening, decrease the amount by 15% at 5,000 feet, 25% at 7,000 feet. Another rule of thumb, because flour dries out faster at high altitudes (yes, flour has water in it), you want to add an extra two tablespoons of liquid for every cup of flour.
Having always lived in the plains, that’s about all I know on the subject. Real scientists — or real high-altitude bakers — please weigh in with any corrections or additions!