“Bread flour vs. all-purpose flour…what’s the difference?”
“Can I substitute one for the other?!”
Desperate texts pinged in succession as my friend navigated her first sourdough loaf. It was the great sourdough boom (and subsequent flour shortage) of 2020, but it wasn’t the first time I’d fielded an onslaught of similar questions. As a professional baker, I’m the bread and pastry guru of my friend group, and I can’t tell you the number of times I’ve been asked whether there’s a difference between bread flour or all-purpose flour. What if you’ve run out of one and have the other? Can you substitute? The answer: It depends on what you’re making. Bread flour and all-purpose flour are not the same, but knowing what distinguishes one from the other—as well as how to manipulate gluten—will help you become a better and more adaptable baker. Let’s start with the basics:
What is flour?
You can find an assortment of flours in most grocery stores these days, including cake flour, self-rising flour, whole grain flours like rye and spelt, and even gluten-free flours made from coconut, almond, or buckwheat. But we’re here to talk about wheat flour, which is made by milling whole wheat berries (comprised of the endosperm, bran, and germ) into a powder.
To create white flour (a category that includes cake flour, bread flour, and all-purpose flour), the bran and germ are sifted out during the milling process. Although some bakers use freshly milled stone-ground flour, most mass-produced flour is made with large industrial roller mills that crush the wheat berries. This flour is then heat-treated to become shelf-stable and may be bleached with chloride or another additive to quickly dry it out, producing a brighter, whiter flour and prolonging shelf life.
Unbleached flour is technically also bleached, but only through gradual aging and controlled oxidation. The flour slowly dries out and its natural yellow hue fades to a creamy off-white—in bleached flour, chemical additives like benzoyl peroxide make the process go more quickly. Performance-wise, you can substitute bleached and unbleached flours for each other in a pinch, though some recipes may call for one specifically. You may notice subtle differences: Bleached flour is somewhat finer and lighter, whereas unbleached is a little more flavorful.
So, what is all-purpose flour?
Exactly what it sounds like: all-purpose! It’s the baking pantry workhorse, a versatile white flour that can be used in almost any baking application. All-purpose flour is what I reach for when I’m making my favorite treats, like quick breads and cinnamon rolls.
The protein content of all-purpose flour ranges from 9% to 12%, depending on brand (more on that below). My favorite all-purpose flour, King Arthur’s Unbleached All-Purpose Flour, has a protein content of 11.7%—this is on the high end of the AP spectrum, but it’s still considered a midrange percentage. While using cake flour (around 9% protein) or pastry flour (around 8% protein) for the baked goods mentioned above would result in loftier, more tender bakes, the truth is that all-purpose flour will often work just fine. Unless you’re making a delicate, airy cake, such as chiffon, which you plan on serving to a pastry chef, most people will not be able to tell which flour you used.
Okay then, what is bread flour?
Bread flour has a higher protein content than all-purpose flour, ranging from 12% to 14%. That makes this type of flour ideal for all kinds of bread recipes, including hearty sourdoughs, tender brioche, and lacy English muffins. As these doughs proof, the strength and elasticity provided by the high protein content allows the doughs to expand and trap carbon dioxide bubbles produced during fermentation.
