This post likely would have been much more helpful about fourteen months ago, when the baking craze started in full force, but better late than never. Hopefully people still bake on occasion? Today we’re going to talk about yeast, a reasonably simple subject that gets complicated surprisingly quickly.

Before we get into the precise details of the baking yeast we use today, it’s important to understand just a bit about the history of bread and leaveners in general. A leavener – basically anything that makes dough rise – can be physical, chemical or biological in nature. Physical leavening agents are air and steam, which might be incorporated either through mixing or through the oven’s heat. Chemical leaveners, most often baking soda and baking powder, create a chemical reaction that causes doughs to rise. And finally, yeast acts as a biological leavener; yeast is a microscopic organism that consumes simple sugars and creates carbon dioxide gas as a byproduct of fermentation, which in turn causes dough to expand. Yeast cells used in baking are found either in commercial packaged form or wild in a starter.

Yeast-risen doughs really are simpler than this picture makes them seem.

Prior to the introduction of standardized commercial yeast, breads were always made with wild yeasts – that is, random colonies of microorganisms floating around peacefully in the air. This is the basis of “sourdough starter,” a mixture of flour (typically wheat) and water left to ferment on its own timetable. Sourdough is a bit of an American misnomer since not all wild yeasted breads need necessarily be sour; “naturally leavened” is a better term, and one that clearly states that no commercial yeasts were incorporated. Because yeast strains are so hyperlocal, naturally leavened bread will always possess unique characteristics depending on where it’s made. San Francisco might be famous for its sourdough due to its humid maritime climate, but a starter transported from the Bay Area to Colorado will eventually shift entirely to local strains of available yeast, thus changing the bread’s flavor. Many professional bakers prefer the challenge and variability of working with starters and wild yeasts, but commercial packaged yeast yields much more consistent results for home bakers.

The commercial yeast we know today has only existed since the nineteenth century; it was originally a byproduct of the brewing industry. Commercial yeast is a standardized product, now always a carefully-cultured strain of Saccharomyces cerevisiae made (at least in the U.S.) with molasses wort. Although supermarket yeast is readily available (except during a global pandemic) and produces remarkably consistent results, the names and packaging can be confusing. Hopefully we can clear that up, and help you produce amazing homemade breads and other baked goods!

Proofing active dry yeast in warm liquid is essential before mixing your dough.

Active dry yeast is probably the most common yeast available to home bakers. Sold in individual packets, small jars or bulk packages, active dry yeast must be “activated” before use by proofing it in a warm liquid (often water or milk, depending on the recipe). Because active dry yeast is dormant when it’s sold, the proofing step “awakens” the yeast, and since a small amount of honey or sugar is typically used, the now-awake yeast cells also have something to feed on after their long nap. Active dry yeast is great for home bakers because the proofing step guarantees that the yeast is still fresh and suitable for use, but it’s always essential to note that the proofing liquid needs to be just lukewarm – about 100 to 110 degrees F. Yeast won’t activate in temperatures that are too cold, and liquids that are too hot (over 135 F) will kill the yeast immediately.

So many names! So much unnecessary confusion!

Next to active dry yeast on the shelf, you’ll likely also see instant yeast. Instant yeast might also be labeled as “quick-rise” or “rapid-rise” or even “pizza yeast,” all of which confuses the situation even further. Instant yeast has been milled to a much finer consistency, meaning that the granules dissolve quicker and can be added directly with other dry ingredients in a recipe, rather than proofed as mentioned above. The downside to this, of course, is that if your yeast is dead, you won’t know about it until whatever you’re baking comes out of the oven without any rise whatsoever. Instant yeast also often includes enzymes and other secret ingredients that help doughs rise faster, cutting down or even eliminating much of the advance work of baking. Instant yeast can also take higher temperatures than active dry can. Many guides indicate that active dry and instant yeast can be used interchangeably, but I think it’s important to understand the science behind both and figure out which is the best choice for the recipe you’re making.

Starter, as mentioned above, is simply an unpredictable mixture of wild yeasts captured in a roughly equal mixture of flour and water. Starters need to be kept active by discarding and then feeding, and thus are a bit more complicated than simply opening a packet of yeast. Naturally leavened breads need much more rising time than those made with strong commercial yeast; I use my starter for overnight loaves with a long, cool fermentation. If you’re maintaining a starter, take care never to introduce packaged yeast into your original container; the commercial S. cerevisiae is so strong that it will quickly multiply and take over your entire starter, pushing out your carefully collected wild yeasts. One wonderful aspect of keeping a starter alive is that you always have some to share if others are looking to experiment with naturally leavened breads.

Fresh yeast, also called cake yeast or compressed yeast, is virtually never seen in America. It is highly perishable, always kept refrigerated, and typically only used in professional bakeries, and only rarely even then. I attended culinary school in France and did learn to bake with it there, but I never use it here. Many of my vintage baking books reference fresh or cake yeast; if you want to try an old recipe that calls for fresh yeast, look up a conversion chart so you can use standard dry yeast. Should you find unexpectedly yourself with a block of fresh yeast, use it as quickly as possible.

Delicious! Nutritious! Great for vegans! Not great for bread baking!

And just to keep you on your toes, there’s also nutritional yeast! If you adhere to a vegan diet you’re likely already familiar with these bright yellow flakes. Nutritional yeast offers a savory, cheesy flavor not often found in plants, as well as a rare non-animal source of vitamin B12, and as such is indispensable in most vegan diets. While nutritional yeast is actually the same S. cerevisiae strain used for baker’s yeast, it is entirely deactivated and so cannot – I repeat, cannot – ever be used in bread baking, as it simply won’t work at all. Nutritional yeast is useful for a variety of reasons, and thankfully is far more widely available now, but please do not attempt to substitute nutritional yeast for any other format of baker’s yeast.

A few other tips for working with yeast: remember to get a good thermometer and keep it handy if you’re not confident about what “lukewarm” actually means; temperature really matters when it comes to yeast. If you only have instant yeast but want to make a recipe calling for active dry – or vice versa – use this handy conversion table. If you bake frequently, skip the individual packets, which are surprisingly expensive, and buy yeast in bulk at a restaurant supply store. These bulk packages usually only cost about $5 and have over a hundred times as much yeast for about twice the money – a spectacular value! You can store your yeast in the refrigerator, but in our dry desert climate I never have trouble keeping it at room temperature. If you have yeast of questionable freshness, test it by combining the packet (always about 2 ¼ teaspoons in U.S. measurements) with ½ cup of lukewarm water and one teaspoon of sugar. Stir gently; after about ten minutes, the mixture should be bubbly and creamy, and can be used as directed. If nothing happens, the yeast is dead – don’t waste the rest of your ingredients. And buy some new yeast.

Two very helpful baking books, especially if you’re at altitude.

If you’re baking at altitude, as I am, know that it’s usually a good idea to reduce the amount of yeast called for in bread doughs. The lower air pressure at higher elevations causes the yeast cells to become overly enthusiastic and the dough may well rise far too fast, which will compromise flavor development and oven spring. Overproofing is a big risk at altitude, and will negatively affect the final product.

In addition to the liquid temperature influencing yeast activity, the ambient temperature has a huge impact on yeast-risen doughs, too. My baking technique shifts quite a bit between winter and summer, as I have to adjust to temperatures that might be too cold (place the dough bowl on top of the gas fireplace!) or too hot (slow the rising by refrigerating the dough!).

One of the best tips I’ve ever seen in reference to baking is to “watch the dough, not the recipe.” It all seems unnecessarily complicated, but like anything else, baking takes practice. With experience, the ingredients and the techniques become simpler and easier to understand, and you start adjusting your doughs based on your senses, rather than what the recipe says. When you bake regularly, you start to learn how the dough will behave and how to create the ideal environment to yield a perfect finished product. Yeast-risen doughs are truly a living thing, and often adjustments need to be made.

Hopefully this post has clarified rather than muddied the topic of the different yeasts you might find in your local grocery store. As always, we’re here to help with any baking questions, so please contact us if we can offer any guidance. Wishing you lots of fresh homemade bread this week and always, dear friends.