What is Yeast, How Do You Bake With It, And What is the Difference Between Instant and Active Dry

This article is part of the Basically Guide to Better Baking, a 10-week, 10-recipe series designed to help you become a cooler, smarter, more confident baker.

Adding yeast to dough is a lot like adding money to a 401(k). It’s hard to know what’s happening (or if anything is happening). The hope, presumably, is that the money grows, but it all feels a little bit nebulous and a lot bit confusing. What are you even doing? What even is a 401(k)?

By the same token, yeast is elusive, mysterious, and (I think) way more alluring than personal finance. Yeast should make the dough grow, but what is yeast exactly? How does it work? And what are all the different types? We’re breaking it down below:

What is yeast and how does it work?

Yeast are single-celled microorganisms that belong to the fungi kingdom (along with mushrooms and, ew, mold). Since ancient times, bakers have been using the yeast species Saccharomyces cerevisiae to make bread rise. (Different strains of the same species are used to ferment beer and wine.)

In bread baking, the yeast feeds off sugar—those in the flour and any added to the dough itself—and converts them into carbon dioxide and alcohol. The carbon dioxide gets trapped within the dough, causing it to expand. (See those gassy bubbles in the photo above? They’re signs of life!)

When the dough goes into the oven, fermentation increases: The yeast frantically feed until they perish at 145° F (R.I.P.), which causes the often-dramatic ballooning in the size of your dough during the first stage of baking (that’s called “oven spring”).

What are the different types of yeast called for in recipes?

Yeast is all around us all the time! This very second. A sourdough starter, the foundation of sourdough bread, is made with wild yeast that’s captured from the air, then fed with flour and water (it’s like an ant farm for microorganisms). But commercially made yeast is better for beginners because it’s easier to work with and produces more consistent results.

You’ll see two main types of dry yeast at the grocery store. Active dry yeast, which often comes in flat packs of three, is what we call for in our Shockingly Easy No-Knead Focaccia because it’s the most widely available. The granules are large—they’re actually made up of live yeast cells surrounded by dead cells (that’s right, not all of the cells are alive) and a growth medium. The yeast is most often activated in warm water or milk, sometimes with a source of sugar, before it’s incorporated into the other ingredients. (If you’re confused, just remember: Activate your active dry yeast.) This hydration phase also gives you a chance to make sure that the yeast is alive—more on that below.

The alternative to active dry yeast is instant yeast, which is finer and can be mixed directly into the dry ingredients, no activation necessary. It contains 100-percent living cells, which means that instant yeast is more powerful than active dry. If a recipe calls for active dry yeast but you want to use instant, a good rule of thumb is to decrease the volume by 25% (for example, if a recipe calls for 1 tsp. active dry, use ¾ tsp. instant). Instant yeast also has a longer shelf-life than active dry: It’s often sold in bulk and can be kept in the refrigerator for years! If you bake a lot but can’t find instant yeast in your area, it might be worth it to buy it online.

What do you need to know before working with yeast?

1. When working with active dry yeast, check the expiration date.

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