Leaveners: a primer

What you need to know about the different leavener varieties:

Active dry yeast comes in small packages in the dairy section. It needs to hang out in warm water for a few minutes before you use it - this wakes the yeast up and gets it ready for your recipe. Check expiration dates, and keep packets in a cool, dry spot.

Rapid-rise (sometimes called instant) yeast is a hardy strain of yeast, and does not need to be hydrated before using. While it doesn't actually rise more rapidly than any other yeast, you get to skip the step of hydrating, making the process a little faster.

Fresh yeast is a favorite of hard-core bakers. It makes delicious, flavorful bread, but it's hard to find and needs to be used up quickly. If you do have access to fresh yeast, use 0.6 ounces per packet of active dry in the recipe.

Sourdough comes from a starter, which is basically an active yeast culture. You can make it on your own (by combining organic flour, water and sugar, and allowing it to ferment) and keep it indefinitely. While it takes longer than yeast, it pays off in flavor.