Baking Central: Buttermilk Biscuits show how leavening works

Being a home baker is kind of like being a magician.

You assemble a list of ingredients, place the resulting mixture in a hot oven, and — abracadabra! — there emerges an airy cake or a lofty loaf of bread or a pan of flaky biscuits.

It's tempting to take a bow — oh, go ahead; you deserve it. After all, you did wield the magic wand called the leavening agent, or the ingredient that makes baked goods rise. This usually is baking powder, baking soda or yeast.

Each has distinct characteristics that promise success. Each also has its own potential for failure. But understanding how and why each agent behaves as it does will improve your baking.

Yeast is familiar, but also can be intimidating. For starters, it's alive, made of single-celled organisms. When mixed with flour and water, yeast breaks down flour's starches into sugars that the yeast then consumes. The byproduct of this process is carbon dioxide gas, which becomes trapped inside air pockets of a well-kneaded dough.

As the gas expands, so does the dough.

Yeast has a temperamental reputation due to the need to activate it in warm water. If it becomes bubbly after a few minutes, it's deemed alive and active, hence the label of "active dry yeast."

But water that's too hot can kill the yeast; too cool, and the yeast may not awaken. The ideal water temperature is 105 degrees — if you happen to have an instant-read thermometer handy.

Happily, there's now instant dry yeast, which you can mix directly into the flour. Instant yeast may be labeled as bread machine yeast, quick-rise yeast or rapid-rise yeast.

By the way, a packet of yeast contains 2 ¼ teaspoons of yeast. With instant rise, you can measure slightly less, an even 2 teaspoons.

Sourdough starters draw on the natural yeast spores in the air, capturing them in a slurry of water and flour. Sourdough starters are the stuff of lore and vary according to the particular climate in which they live, which is why San Francisco sourdough tastes different from one made in St. Paul.

Making your own starter takes several days and requires even more time to reach prime leavening strength. A wealth of research in books and on the internet will lead an aspiring sourdough baker through the process.

Quick breads, on the other hand, explain themselves.

They rise quickly, inflated by the leavenings of baking powder and baking soda, which look alike but are not interchangeable. Some recipes call for both, some for only one, for specific reasons. Chemistry lies ahead:

Baking soda is an alkaline powder. To produce carbon dioxide, it needs to be activated by an acidic ingredient such as buttermilk, lemon juice, vinegar, yogurt or even molasses.

The key thing to remember about baking soda is not to think that more is better (as some may regard the addition of chocolate chips in a recipe.) In other words, follow the recipe. It has the proper proportions of soda that can be fully activated by the acidic ingredient. Too much unactivated soda will leave a bitter taste that no amount of butter can hide.

Baking powder is a leavening created by combining alkaline baking soda with acidic cream of tartar. Because it's already acidic, it's activated simply by adding a liquid — water, milk, cream, etc. (You can even make your own baking powder: Mix two parts cream of tartar with one part baking soda and one part cornstarch, which acts as filler.)

If you do a lot of baking, chances are your baking powder is powerful. But it can lose potency over time. If you want to check its oomph, add 1 teaspoon to a cup of hot water. If it immediately bubbles, it's good. If not, toss it.

For many years, the challenge of using baking powder is that it starts working as soon as it's moistened, so once your dough or batter was mixed, you wanted to get it into the oven as quickly as possible before the leavening expended most of its power.

These days, however, most baking powder is "double-acting," meaning that it starts working as soon as it's combined with liquid, but also has powder that doesn't "act" until it hits the oven's heat. Still, don't dally. Having your ingredients and tools ready to go ensures that your baked good will get the most lift.

Why do some recipes call for both baking powder and baking soda? Mostly, it boosts the amount of lift. But baking soda also enhances browning, which can make a more attractive baked good.

How all of this chemistry comes together on your plate may best be illustrated by the recipe for a classic biscuit. Many recipes use only baking powder, but we like the extra flavor of buttermilk, which enables us to use some soda, which also helps the biscuits brown.

Double-acting baking powder also lets us fuss just a bit longer than a simple roll-and-cut. Patting, cutting and layering the dough two times results in especially flaky biscuits.

Finally, pro tip: The action of pressing a biscuit cutter through the dough (pushing straight down; no twisting) can make the edges of the layers bend down. Flipping the biscuits before placing them on the baking sheet counteracts this bend, encouraging them to rise as high as possible.

See, leavenings aren't so magical, once you understand the science.

Kim Ode is a freelance writer from Edina. Reach her at odekim@gmail.com.