So then, if baking recipes scale about 99% of the time, in what instances don’t they scale? Oh sure, put me on the spot readers Robin, Carl, Heather, Sandi and Monica. But that’s a really good question. Most incidences of non-scaling have to do with chemical leaveners — especially baking soda, for the simple reason that once you get soda wet in the presence of an acid, the leavening reaction tends to happen quickly. So quickly that it can peter out before you get you’re panned…whatevers…into the oven. This was especially true in our grandmothers’ day (these days soda manufacturers have tweaked the product so more of the bubbling action happens when the soda gets hot) but it’s still a risk to the contemporary baker.
Baking powder is less prone to the petering-out problem, though the wetter the mixture, the faster you’ll lose your pop. This is why some pancake batter recipes — even though they don’t contain baking soda — explicitly state that they can’t be doubled. The writer calculated that by the time you’d griddled all your cakes the last few would have the texture of frisbees.
Reader Mary correctly observed that batters for very large wedding cake layers don’t scale, and that you must cut back on your leavening as the pan gets broader. The reason for this has to do with physics more than chemistry, for the reality of broad, flat layers is that pan walls provide rising batter with support (mostly by facilitating heat penetration, which helps the batter set). The farther out into the center of the pan you get, the more unstable the cake becomes. This is why big sheet cakes often fall in the middle: they rise, can’t support themselves, and collapse. Cutting back a little on the leavening creates a slower rise, which gives the center of the cake more time to set and reinforce itself as it pushes upward. You lose a little in volume, but you gain a flatter center.