When I first set out to become a sourdough baker, the only thing I really knew about it was that sourdough bread has a distinct taste. I can call to mind the taste of a sourdough bread bowl from the Boudin Bakery in San Francisco, and the bakery loaves my mom brought home from the grocery store in Northeast Ohio. I knew a starter would change the taste of my bread, but I didn’t realize just how different baking with sourdough actually is.
To save you some time figuring that out for yourself, I’ve compiled some basic facts about wild yeast, sourdough cultures, and how they are used in baking.
What, exactly, is sourdough?
Sourdough bread is made with a fermented dough (literally, a “sour” dough) that contains wild yeast and a type of bacteria called lactobacilli. The lactobacilli produce lactic acid from sugars, giving off the “sourdough” taste we recognize in bread. Species of this same bacteria are also used in other fermented foods such as yogurt, cheese and beer.
How do these things get into bread?
Believe it or not, wild yeast and lactobacilli are already present in the flour you buy at the store! Unbleached, whole grain flours contain more of these microorganisms, which is why starter recipes often call for some whole wheat or other whole grain flour. Wild yeast is also present in the air all around us, and lactobacilli in the human body. Difference in sourdough taste can be accounted for by the variations in flour, the baker, and the environment in which the starter and bread are made.
All it takes to turn that flour into a sourdough culture is water and time. Adding water to flour makes it possible for the amylase enzyme to break down the starch in the flour into glucose and maltose. Natural yeast metabolizes these sugars, giving off CO2—which is what makes sourdough bread rise. Meanwhile the lactobacilli can metabolize other sugars that the yeast cannot, producing the sour taste.
Sounds like a lot of science—is baking with sourdough difficult?
Although baking with sourdough might sound like a difficult task, keep in mind that until pretty recently in history, sourdough was the primary method for raising bread and it was almost certainly discovered by accident. Think about it—all it would have taken is one baker (likely an ancient Egyptian) leaving some flour and water out a little too long, noting the gas bubbles that formed in the mixture, and folding the mass into a fresh batch of bread dough. Voila, sourdough bread!
It was common for ancient bakers to simply hang on to a piece of dough from each batch of bread and use this as leavening for the next day’s bread. Humans later figured out how to harvest yeast produced in the beer making process and used this to make bread. Commercial baker’s yeast didn’t even exist until the end of the 19th century, and the granulated variety we’re used to today wasn’t developed until World War II. For most of human history the only leavened bread available would have been made with sourdough.
If ancient bakers could do it, so can you. We modern bakers just have the benefit of scientific research into microbiology and kitchen scales that help us achieve more consistent results!
Your mileage may vary. Although we do have science on our side, every starter, baker and climate are still different. I bake with a 100% hydration starter made with both all-purpose and whole wheat flour, in the fairly humid climate of Southwest Ohio. Sometimes this means I might need a little more flour in my dough or on my work surface. Or that my bread will rise faster on a hot summer day. Use recipes and their measurements as guidelines, but learn to rely on your own observations and don’t be afraid to adjust for best results.
Baking With Sourdough and What to Expect
If you’re thinking about getting into sourdough, chances are you’ve had past experience baking quick breads or yeasted breads. Sourdough is a bit of a different beast. Unlike commercial leavening agents like baking powder/soda and baker’s yeast, natural yeast needs time to work and that affects how you mix, handle and treat the dough. You may need to adjust some of your expectations about baking! Namely:
Sourdough takes longer. It simply takes a longer time for natural yeast to raise a dough. In recipes where you are relying on your starter as the sole leavening agent, expect that bulk fermentation (the first rise) will take at least 4 hours and perhaps up to 24 hours or more.
Sourdough is often hands-off. The trade-off for long baking timelines is that your hands-on time is pretty minimal. The yeast needs time to work, and bakers need to give it time.
Sourdough has different handling requirements. You might be used to the long periods of kneading required by pizza dough or other breads. Not so with natural yeast. Because of the long fermentation times, bakers tend to rely on gentler and easier methods like “stretch and fold,” where you simply fold the dough over itself a few times in the bowl, repeating a couple of times during the bulk ferment stage. Over time the folding technique builds and aligns gluten strands in the dough, lending it structure—the whole goal of kneading anyway.
These things are not universally true about sourdough, and many recipes will use a combination of natural yeast and baker’s yeast to get the taste of sourdough but the rise and speed of a conventional bread dough. Before baking with your starter, you should understand its role in the recipe:
Sourdough starter can have different functions in your recipe.
As a flavoring. Think pancakes, quick breads, cakes and other recipes where you might want a little sourdough tang, but there’s some other leavening agent like baking soda. If you add starter to a recipe, leave out an equivalent amount of flour and water.
For example, if your recipe calls for 1,000 g flour and 400 g water and you want to add 200 g of 100% hydration starter (equivalent to 100 g flour and 100 g water), you would then use only 900 g flour and 300 g water. A good rule of thumb is to replace no more than about 1/3 of a recipe’s flour with starter. See King Arthur Flour’s tips for when and how to add sourdough to a recipe.
As one leavening agent, in a hybrid dough that also includes baker’s yeast. Most bread recipes can be adjusted to incorporate sourdough as part of the leavening, by reducing the amount of baker’s yeast and increasing time for bulk fermentation. I often make pizza dough that uses both sourdough and yeast, for example. It takes slightly longer than a dough made with commercial yeast alone, but it rises a bit more and tastes better!
As a preferment. Some breads like ciabatta and baguettes rely on a mixture of flour, water and yeast, typically left overnight to ferment before being added to the main dough the following day. (There are also names for specific types of preferments–a poolish, for example, is a thinner preferment with more water, while a biga is a stiffer one.) The purpose of the preferment is to add flavor and complexity to the bread, as well as a little extra oomph to the bulk ferment. Your sourdough starter can be used as a preferment shortcut to add flavor, while you rely on the leavening power of commercial yeast for the rise.
As the only leavening agent. Pure sourdough breads will need longer rise times than baker’s yeast (think 12+ hours instead of 1-2 hours). Exact timing will depend on the starter’s activity, climate, and more, but expect full sourdough breads to take at least 24 hours from start to finish. The good news? Most of that is going to be hands-off time! See the timelines in my Basic Sourdough Baking Method post for more information.