Have you ever wondered which yeast you should use when baking?  What's the difference between active dry yeast and instant yeast?  What the heck is compressed yeast and fresh yeast?  Can you use Rapid Rise yeast if a recipe calls for active dry yeast?  Well, I've wanted to do a yeast post for a while now.  I get asked from time to time about the differences in yeast and I know there is a lot of mystery about it.  So I'm going to clear it up for you and demystify the whole yeast question.

I use yeast a lot.  We make homemade pizza once a week, I'm always making focaccia and other breads and my yeast of choice is instant dry yeast.  I have no brand loyalty on this - I buy Rapid Rise or Quick Rise, whatever the store has.  I keep it in the refrigerator, although it has a very long shelf life, but I try to bring it to room temperature before I use it.  Let me explain why I use the instant kind.

First of all, there are basically two kinds of yeast - fresh, compressed yeast in cakes and dry yeast.  Fresh yeast is something most people do not use anymore and many stores don't bother to carry it.  It has a very short shelf life (two weeks or less) and is highly perishable.  Because of this, manufacturers developed dried yeast, or "active dry yeast."  It enables yeast to be stored for a long time.  In this particular drying process, some yeast cells are killed and so that is why it is best to "proof" active dry yeast in some warm liquid, to make sure that enough yeast cells are still alive to do the trick with your dough.  Manufacturers got even more clever and came up with a different drying process, one that left a whole lot more yeast cells alive - this is "instant dry yeast", better known as Rapid Rise (Fleischmann's brand) or Quick Rise (Red Star brand) or Perfect Rise (SAF brand). They do not require proofing or rehydration to work.  They are designed to be added right in with your dry ingredients.  These instant dry yeasts are all the same thing and are packaged the same, also - in 1/4 ounce little envelopes. Instant, or quick rising yeasts, will do the job of rising your doughs about 50% faster. They are more stable and reliable and a lot of people prefer them.  Also, the yeasts that are labeled "For Bread Machines" are instant yeasts.

Are they interchangeable?  Remember, the biggest difference is that active dry yeast needs to be proofed and instant yeast does not.  Aside from that, you can substitute one for the other in a recipe - you just use a little less instant yeast if a recipe calls for active dry yeast.   Peter Reinhart, the Zen master of bread baking, actually prefers instant dry yeast because it is easier to use, it's stronger and you need less of it.  In fact, he believes instant yeast will be the most used someday because of all of its strong points.  His formula for switching them is this:

Multiply the amount of instant yeast by 1.25 for the equivalent of active dry yeast.

Basically,  you use 25% less of instant yeast than active dry.   Frankly, I'm very loosey goosey with my yeast measuring.  Because I use instant yeast and I don't have to proof it, I know it's going to do the trick, no matter if I use 1 teaspoon or 1-1/2 teaspoons.  I usually just eyeball it in my hands, unless I'm making a recipe that I am not familiar with and then I actually get out the measuring spoons.  But I've made focaccia and pizza dough hundreds of time and I'm beyond measuring. See?  It's not that scary.  Instant yeast will just make your dough rise faster.

Why use active dry yeast, then, over instant yeast?  Some people believe they can taste the difference, but this is really in the rising times, not which yeast you use. The less yeast that goes into a dough and the longer the dough rises, the better the flavor the dough will have.  Bakers know slow rises are better for taste, but, as I said, this is a function of the length of time the dough is allowed to rise, not which type of yeast you use. Remember, yeast is yeast is yeast.  It's all the same - if you want a slow rise and you are using instant yeast, just use less.

Judith Jones (the editor who originally got Julia Child published) writes a funny story about the yeast debate in her book, "The Tenth Muse - My Life in Food".  She recounts working with the legendary Marcella Hazan in her early days on a cookbook and clashing with her over the use of acive dry yeast.  Marcella insisted on using fresh, compressed cake yeast but Judith Jones thought this was not practical for the average American home cook and suggested the recipe call for the more modern active dry yeast.  Marcella was doubtful, saying that the taste would not be right.  She insisted they do a taste test and so she baked breads with both kinds of yeast.  No one (not even the great James Beard, who was invited to take part) could tell the difference between the breads.

Some helpful notes on using yeast: 

Instant Yeasts are Rapid Rise (Fleischmann's), Perfect Rise(Red Star)  and Quick Rise (SAF).  They're all the same thing.

No rehydration is required of instant yeasts.  Fleischmann's says on their web site that RapidRise™ yeast actually loses its fast rising capabilities if dissolved in liquid, and will require two complete rises.  I assume that holds true for other instant yeasts.

Active Dry yeast has larger granules and is necessary to dissolve completely for the yeast to work. Therefore, Active Dry works best if dissolved in warm water (100° to 110°F).

One envelope (2-1/4 tsp) of yeast (active dry or instant) can raise 4 cups of flour (or about 1 pound)

Yeast dies at 140 degrees F, so be sure that the liquid you add to your dough is not hot.  It should be warm, about 95 - 110 degrees F.  Use a thermometer until you remember how warm it should feel and then you can just do it by touch.  Mr. Food Science himself, Harold McGee, says that yeast activity is best at 95 degrees F/35 degrees C.

Salt can kill yeast or decrease its effectiveness if it comes in direct contact.  For this reason, add the salt in a recipe along with the bulk of the flour, when you add that.

1 envelope of yeast is about 2 -1/4 teaspoons.

You don't have to refrigerate yeast, but if you do, it's better to bring it to room temperature before using.

Some recipes using yeast:

How to Make Homemade Pizza

How to Make Focaccia Bread

Italian Easter Bread

Pizza Quattro Stagioni