The simplest definition of sourdough comes from the dictionary: leaven, especially fermented dough retained from one baking and used, rather than fresh yeast, to start the next. But sourdough is so much more than simply a way to make bread rise.
It's an enticing, tangy flavor; a snapshot of American culinary history, and a classic ingredient in everything from pancakes to pretzels. It's a part of the family for its aficionados—a living ingredient that thrives on flour and water and love.
And most of all, it's an endlessly fascinating subject for bakers of all stripes. From the beginner first picking up a bowl and spoon to the veteran who's kept a starter happy and lively for 30 years, sourdough reaches out and grabs our imagination, reminding us that the simplest beginning—flour and water—can lead to magic.
What is sourdough, anyway?
Sourdough refers both to bread, and to the starter used to make it. Sourdough starter begins with a combination of flour and liquid. The proportion and type of flour and liquid can vary dramatically, from a stiff starter made entirely with rye flour and water, to a liquid batter of milk and cornmeal, and everything in between.
Friendly bacteria (lactobacilli), present in our natural environment; and the wild yeast attracted to and living on flour begin to work with one another when flour is mixed with warm water. The result: sourdough starter. These tiny living creatures (lactobacilli and yeast, collectively called the sourdough's microflora) generate byproducts that cause bread to rise and give it complex, rich flavor.
But sourdough starter's not just for bread. Our early settlers used it to leaven pancakes and biscuits; today, we enjoy sourdough starter in treats as diverse as chocolate cake and pizza, where we value it for its rich, complex flavor as much as its ability to make things rise.
How does sourdough make things rise?
Wild yeast is a tiny fungus. It exists all around us in varying degrees—in the air, settled on work surfaces, and in some of the ingredients you bake with: most importantly, flour.
Lactobacilli are also all around us. They have a wonderfully symbiotic relationship with wild yeast; when the two are brought together with flour and water, the result is high-rising, delicious bread, or light, fluffy pancakes.
How does it all work to make dough rise? Lactobacilli (remember, they're all around us; you don't need to "add" them) break down flour's complex carbohydrates into simple sugars—exactly what yeast needs for food. The yeast, feeding on these simple sugars, produces carbon dioxide bubbles. The elastic wheat gluten in bread dough traps these carbon dioxide bubbles, causing the dough to expand as if it contained a million tiny balloons.
When you put a risen loaf into the oven, the yeast quickly dies; but the CO2 it generated remains trapped beneath its flour/water matrix, producing a golden loaf of beautifully risen bread.
Where does the sour flavor come from?
As byproducts of manufacturing simple sugars, lactobacilli produce flavorful organic acids: lactic acid, which adds a rich, mellow flavor to bread; and to a lesser degree over a longer period of time, acetic acid, which gives sourdough bread its sour tang.
To take a short deep dive here, there are two types of lactobacilli: homo-fermentative, which produces primarily milder-flavored lactic acid (think yogurt); and hetero-fermentative, which produces lactic acid, but also stronger-flavored acetic acid (think vinegar).
Since homo-fermentative lactobacilli do well at room temperature, dough raised at room temperature will generally yield a milder-flavored bread. Hetero-fermentative lactobacilli prefers temperatures around 50°F; so raising bread dough in a cooler spot (as cool as the refrigerator) will bring out its vinegary acidity.
By varying the liquid/flour balance of your starter, and the temperature at which it's fed; as well as the temperature and duration of a sourdough loaf's rise, you can make sourdough bread that's richly flavored, with barely a hint of sour; or one that's truly mouth-puckering.
Is there a “right” way to make and use sourdough starter?
There are scores of self-proclaimed sourdough experts out there, each willing to share with you the "secret" to sourdough. Problem is, these "secrets" are often completely contradictory. Sourdough is an area of enormous controversy, as well as firmly held ignorance.
One business claims you can only capture the elusive wild yeast by buying their special packets. A cookbook author has you set out a bowl of grapes and leave them untouched for two weeks, hoping the yeast will spring to life on its own.
"Scientific" bakers hold that sourdough bread can't be made without a thorough understanding of the symbiotic chemical relationship between yeast and lactobacilli. At the same time, people made bread with wild yeast for millennia—so how complicated could it be? These wild swings between science and superstition make the sourdough sphere more intimidating than it needs to be.
We know that it is yeast and lactobacilli—not magic—that leaven and flavor sourdough bread. We also know that temperature and hydration (the liquid/flour ratio) are important. But bakers' intuition is as essential to sourdough success as pure science. We see the same flour/water combination behaving differently from one time of year to another (or even from day to day); and it's as much experience as science that teaches us what's going on, and how to adapt.
So look at everything you read about sourdough as simply one approach. There are as many ways to create, nurture, and bake with a starter as there are bakers in the world. The information you read here works well for us, and we've shared our expertise with hundreds of thousands of satisfied bakers. But the "right" way to bake with sourdough is whatever works for YOU.
Getting started with starter
You can make your own sourdough starter at home. All it takes is flour, water, warmth, and time. Once you make it, the starter needs to be fed and cared for. But its requirements are simple; with a minimum of effort, you can keep starter on your counter, or in the fridge, to use whenever the impulse strikes.
How to make your own starter from scratch
There are lots of other ways to make a starter; as well as many types of starters. We'll concentrate here on a typical American sourdough starter, which begins with whole-grain flour, and is subsequently fed with all-purpose flour. This is the easiest type of starter to successfully maintain, and it will create delicious sourdough breads, waffles, pizza crust, and other tasty treats.
It takes about a week to develop a starter that is strong enough to use for bread baking. Variables like the temperature and humidity of your kitchen, and the flours and feeding schedule you use, will affect the amount of time it takes to make a starter that's ready to use in bread.
Read our complete illustrated recipe for making your own starter.
How to make starter from King Arthur Flour’s historic starter
Looking for a quicker, easier way to make sourdough starter? Here at King Arthur Flour we've been nurturing a sourdough starter that can be traced back at least 100 years. And we've been sharing small jars of that starter-a "starter for starter"-with our customers for decades.
Want to obtain your own piece of this historic starter? We can help »
Once you receive your starter, you'll need to feed it several times to wake it up, a process that takes about 24 hours. Don't worry; unlike a baby, your starter won't need any 2 a.m. feedings! Read our complete illustrated instructions for feeding your King Arthur Flour starter.
How to feed and maintain your established starter
Once you've created your starter, it needs regular feeding. Some dedicated bakers choose to feed their starter every day. Most of us feed on a more casual schedule: once a week is ideal, but your starter can also survive much longer stretches between feedings. Read our complete illustrated instructions for feeding and maintaining your own starter.
Like any living thing, sourdough can be unpredictable. Weather, the "microclimate" in your kitchen, the flour you use for feeding, and how and where you store your starter all influence its behavior.
Sourdough baking is one of the top subjects we address every day on our Baker's Hotline. We've rounded up the most common questions people ask, and have provided the answers in our sourdough FAQS.
For an immediate intervention—whether your bread is "rising sideways," you think you killed your starter, or you simply want some 1:1 help—contact us. We're available via phone, email, or live chat 7 days a week.
Let's stay in touch!
Sign up to receive seasonal recipes, baking tips, special offers, and more from King Arthur Flour.