The first of the “Big Three” leavening methods is chemical leavening. It’s the latest of the three to arrive on the baking scene, having been invented right about the time of the First Industrial Revolution, some 230 years ago. As its name implies, it involves using chemicals to create “seed” bubbles (usually of carbon dioxide) in wet doughs or batters. I say “seed” bubbles because just as with microbes, chemical leaveners can only push a bread up so far. They can initiate the process certainly, but the real heavy lifting is done by steam. And if that sounds like mechanical leavening to you, it’s a because it is. Mechanical (or steam) leavening is part of every leavening method. Whether alone or teamed with others, it is the true engine of bakery.
Category Archives: Leavening Methods
So what is “mechanical” leavening? What is the “mechanism” that results in rising vis-à-vis a microbe or some chemical reaction? In a word: steam. Though to be fair steam is the chief rising agent in any type of leavening. Microbes or chemicals may create the initial bubbles in, say, a loaf of sandwich or banana bread, but it’s steam that’s ultimately responsible for blowing them up. What distinguishes pure mechanical leavening from these other types of leavening is that where mechical leavening is concerned, there is no instigator. The dough must be prepared in such a way that it rises on steam power alone.
Which is no small amount of force, as the steam locomotive amply demonstrates. Sure, if you heat CO2 bubbles up in an oven you’ll get some expansion (maybe a few times their original volume). Heat water though, and the steam that’s created will occupy 1400 times the amount of space that the water originally did. That’s a lot. Yet for all that pure mechanical leavening is one of the least employed of all leavening techniques, at least by home bakers. Probably because the dough preparation for mechanically leavened pastries can be a little…involved.
I’m thinking of course or layered, also known as laminated doughs.
Microbial (also called “biological”) leavening is the grandaddy of all leavening techniques. It dates back to when the first human mistakenly left his bowl of gruel sitting out while he rushed off to join the village mastodon hunt. The result was what we now call a “starter”. And while the biology of microbial leavening can be a bit complex, mechanics are pretty simple: yeasts, as a by-product of their consumption of sugar, create bubbles of carbon dioxide in a dough. Those bubbles fill with steam in the oven, expanding the loaf and lightening its texture. Elementary, my dear Watson.