A loaf of bread isn’t gonna rise on its own. Neither will bagels or muffins. Pancakes will be bereft of fluff. They need the help of leaveners like yeast, baking soda, or baking powder to spring up in the oven or on the griddle. But not all leaveners are created equal; there are times and places for each of them, and instances that call for using more than one. But how do know, when straying from a recipe or creating your own, what to use and when? The more you know about different leaveners and what they are, the easier it is to understand how they’ll behave in different recipes.

Yeast

What it is: It's a kind of living fungus that produces gas, and it’s that gas that makes baked goods rise. Yeast is everywhere and airborne, which is how sourdough bread, inoculated spontaneously via its environment, can rise without the addition of packaged yeast. But the packaged, dried kind we usually bake with is cultured. 

How it works: Recipes with yeast usually call for you to add a little sugar and warm milk or water. The warm liquid wakes the yeast up and the sugar feeds it, which encourages it to produce gas, thus making your doughs rise. It’s worth noting that you can buy cubes of fresh yeast, though they’re harder to find. 

Some bakers insist that fresh yeast yields a better-tasting result, but I don’t think there’s much of a difference. If you want to bake with fresh yeast instead of dried, use four times as much fresh yeast as the recipe calls for dried. So, instead of ¼ ounce dried yeast, use one ounce fresh. Instant dried yeast can be mixed directly into a recipe’s dry ingredients, while active dried yeast needs to be soaked in warm liquid for 5 to 10 minutes before it wakes up.

Typically found in: Sandwich breads, enriched doughs (like for challah, brioche, or cinnamon rolls), pizza dough, focaccia, other thick doughs

When to use it:

When you’re letting something rise for a couple of hours
When you’re looking for a very impressive, airy rise
When you’re making shaped doughs (like for pizza, rolls, or pretzels)
When you want something to taste bready

Baking Soda

What it is: Sodium bicarbonate, an alkaline substance.

How it works: Baking soda, an alkaline, needs acid to activate. They neutralize each other, thus producing carbon dioxide, which then leavens whatever you’re cooking. Think of the old science-fair volcano: baking soda plus vinegar equals boom! Foamy, rising bubbles galore. This is what makes buttermilk pancakes so particularly delicious: The acidic buttermilk interacts with baking soda in the mixture, which leads to lofty, tender pancakes.

Typically found in: biscuits, pancakes, with buttermilk, in thin batters

When to use it: 

When there’s an acid (like lemon juice, vinegar, buttermilk, yogurt, chocolate, coffee) involved
When you want a baked good to brown nicely (pretzels, for example, are sometimes dipped in a solution of water and lots of baking soda to make them brown when baked and give them their signature toasty-bitter flavor)

Baking Powder

What it is: It's a mixture of sodium bicarbonate (baking soda) and, according to Harold McGee in On Food and Cooking, “an acid in the form of salt crystals that dissolve in water”—such as cream of tartar and sodium aluminum sulfate. Many baking powders are double-acting, meaning that they produce the carbon dioxide bubbles a baked good needs to rise twice during the baking process: the first when the ingredients are initially combined, which McGee says is crucial for forming small gas cells in the batter during the first rise and during the second expands these cells to create a final light texture.

Typically found in: quick breads, muffins, cakes, in thin batters

When to use it:

When you’re looking for a good rise without having to wait
When the recipe you’re using doesn’t have acid (since the baking powder already contains the acid it needs to produce carbon dioxide)

Soda and Powder

Some recipes call for both soda and powder. When this is the case, the baking soda’s aim is to neutralize some of the acid in a recipe and tenderize the resulting baked good. Meanwhile, the baking powder does the work of the rising.

Baking soda and baking powder have a chemical, somewhat unpleasant, salty-bitter taste, so both should be used with a light hand—just enough to neutralize the acid and lift the batter.

When to use both:

In recipes that have lots of acid (like, say, a chocolate-coffee buttermilk cake)