What’s the Difference Between Yeasts?

How does yeast work?

When yeast is mixed with flour and water, natural sugars are released. Yeast, like humans, loves to devour sugar. When it does, it creates carbon dioxide as a by-product, which is what causes those lovely bubbles that force your dough to rise.

Egyptians were capturing natural yeasts in the air to bake bread and ferment beer more than 5,000 years ago, but it was a slow and time-consuming process. Fortunately, someone thought to round up those little Saccharomyces cerevisiae and deliver them to your local store. All yeast is not created equal, though.

Dry yeast varieties

1. Active dry

Active dry yeast is the most common form of yeast. It’s what your parents and grandparents likely used. During World War II, Fleischmann’s Yeast invented a shelf-stable granular yeast that’s all-natural and made, quite simply, by evaporating the liquid out of yeast and pulverizing what remains into granules. Active dry yeast is similar in size to cornmeal, can easily be measured, and, prior to use, it must be “proofed” or “active-ated” (a little clue there to its name).

Most recipes that call for active dry yeast provide instructions for dissolving the yeast in warm water or milk (100 to 110°F | 38 to 43°C). You’ll want to keep a thermometer handy rather than rely on guesswork, though, as temperatures over 110°F (43°C) can kill off the little guys.

Proofing also serves as a handy way to test the potency of your fresh yeast prior to adding more of your precious flour. You’ll want to wait 10 to 20 minutes for those sweet little bubbles to form, confirming that your yeast is still viable and that your baking adventures will be successful (or at least not destined to fail because of the yeast). If nothing happens with your yeast, your bread won’t rise. Save your flour.

Active dry yeast can usually be found either in wee single-use envelopes or small jars. When there’s not a rush on baking supplies (we’re looking at you, 2020) active dry yeast is usually easy to find in the baking aisle of any grocery store.

2. Instant yeast (sometimes known as rapid rise or bread machine yeast)

Given our society’s demand for instant gratification, “instant” (or “rapid rise”) yeast was developed. Instant yeast has been pulverized into even finer granules and can be used “instant-ly” (another clue). It’s then supplemented with enzymes and other additives (if you want to get technical, sorbitan monostearate and ascorbic acid) that enable the yeast to dissolve more quickly and cause the bread dough to rise even faster.

Since instant yeast doesn’t need to be dissolved in warm water, you can just toss it right in with the dry ingredients and enjoy those extra 10 minutes you saved not having to proof it. It’s also more heat tolerant than active dry yeast, preferring liquid temperatures of 120 to 130°F (49 to 54°C) to achieve the fastest rise. (Kindly note that although you CAN proof instant yeast without any detriment, that step isn’t necessary.)

Like active yeast, instant can be stored, unopened, at room temperature indefinitely, although once opened it’s best kept in the refrigerator for 6 months or freezer for 12 months. It can also be tossed unopened in the freezer and forgotten about for up to a year and still remain viable.

3. Fresh yeast

Fresh yeast is most often used by professional bakers and can be found in the refrigerated section of some markets. As the name implies, it doesn’t have a long shelf life and must be refrigerated and used within several weeks. Sold in little “cakes” that resemble a beige pencil eraser (that’s where the alternative name of “cake yeast” comes from), you crumble it up with your fingers before using it in a recipe.

Fresh yeast must also be activated or “proofed.” This is easily accomplished by dissolving the yeast crumbles in a bit of warm water (100 to 110°F | 38 to 43°C) with a pinch of sugar. If it doesn’t foam up and act all burbly in 10 minutes or so, chances are it’s no longer viable.

Given the finicky nature of fresh yeast, it isn’t the most practical thing for home cooks who don’t bake bread often.

4. Other kinds of yeast

The rise (hah!) in popularity of instant yeast has lead to many other varieties of yeast formulated for different purposes. Bread machine yeast. “Osmotolerant” yeast (which performs better in sweet doughs containing a high sugar content). Even pizza crust yeast (contains dough relaxers that limit the spring back when rolling out your perfect pie).

Can I substitute one type of yeast for another?

It’s usually best to use the type of yeast specified in a recipe. However, there are times, like during a global pandemic, when a substitution may be required.

Instant and active dry yeasts are pretty much interchangeable. Which you use is really up to personal preference or availability. The most important thing to keep in mind when making a substitution is that the type of yeast will determine how long you need to let your dough rise. If you’re using active dry yeast in a recipe that calls for instant, keep in mind that you’ll need to give the dough 15 to 30 minutes longer to rise. And if you’re using instant instead of active dry, you can decrease the rising time by 15 to 30 minutes. Make sense?

Don’t have any yeast? Never fear. This sourdough starter is made with just flour and water and the natural wild yeast floating around in the air in your kitchen. But it does take a little patience. Want bread NOW? Crack open a beer and let the yeast in it do the work for you with this beer bread. See how much fun science can be? Think of it as homeschooling.