White flour comes from wheat, specifically from the starchy interior of the wheat kernel called the endosperm. Through a multi-step milling process, the outer layers and the nutrient-rich core of the kernel are stripped away, leaving only that white, powdery center behind. The result is the fine, neutral-flavored flour that lines grocery store shelves in bags labeled all-purpose, bread flour, cake flour, and more.
Inside the Wheat Kernel
A single wheat kernel is a tiny package with three distinct parts, each serving a different purpose for the plant and offering different things nutritionally. The endosperm makes up 80 to 85% of the kernel. It’s mostly starch and protein, and it exists to feed the seed as it sprouts. This is the only part that ends up in white flour.
Surrounding the endosperm are the bran layers, accounting for 10 to 14% of the kernel. Bran is the tough, fiber-rich outer shell that protects the seed. It’s dark in color and gives whole wheat flour its coarse texture and nutty flavor. At the base of the kernel sits the germ, a tiny 2.5 to 3% portion that would eventually grow into a new wheat plant. The germ is packed with fats, vitamins, and minerals, but those same fats cause flour to go rancid quickly. Removing the bran and germ is precisely what makes white flour white, mild in flavor, and shelf-stable.
How Wheat Becomes White Flour
Modern flour milling is an industrial process designed to peel the wheat kernel apart without crushing everything together. Before wheat enters the mill floor, it’s cleaned to remove stones, dirt, and other debris, then conditioned with water to toughen the bran so it separates in larger, easier-to-remove pieces rather than shattering into the flour.
The first real action happens at the break rollers: two cast steel cylinders set slightly apart, with the top roller spinning faster than the bottom one. This speed difference creates a shearing action that cracks the kernel open rather than pulverizing it. Opening the grain carefully gives the miller better access to the endosperm particles inside. A typical mill uses up to four sets of these break rollers, each one further splitting already-opened kernels to free more endosperm.
After each pass through the break rollers, the fragments are sorted by size and weight through a complex arrangement of sieves. Bran flakes, being larger and lighter, get separated out. Endosperm chunks move forward. These chunks then pass through as many as 12 sets of smooth reduction rolls, which progressively grind the endosperm into finer and finer powder. At each stage, the finished flour is sifted off, and the remaining particles continue through more rolls until everything has been ground down.
How Much of the Kernel Actually Makes It
Not all of the endosperm ends up in the bag of flour you buy. The initial milling separates flour at roughly a 72% extraction rate, meaning about 72% of the kernel’s weight comes through as white flour once nearly all the bran and germ have been removed. But that flour gets refined again, with about 85% of it eventually sold as “patent” flour, the standard white flour most consumers use. The true extraction rate of refined white flour is closer to 60% of the original kernel. Whole wheat flour, by contrast, has a 100% extraction rate because nothing is removed.
That 40% difference represents a significant amount of fiber, healthy fats, and naturally occurring vitamins that get left on the milling room floor (or, more accurately, sold separately as animal feed or wheat germ supplements).
Why White Flour Is Actually White
Freshly milled flour isn’t pure white. It has a faint yellowish tint from naturally occurring pigments called carotenoids. Left to sit for several weeks, flour gradually whitens on its own as oxygen in the air breaks down those pigments. But waiting takes time and warehouse space, so many commercial mills speed things up with bleaching agents.
Benzoyl peroxide is one of the most common. It oxidizes those yellow pigments, turning the flour bright white. Bleaching also subtly changes the flour’s protein structure, which can affect how dough behaves. Unbleached white flour skips this chemical step and retains a slightly off-white, creamy color, though it’s still refined flour with the bran and germ removed. The word “unbleached” on a label refers only to color treatment, not to how much of the kernel is present.
Different White Flours From Different Wheats
The type of wheat that goes into the mill determines what kind of white flour comes out. Hard wheat varieties have more protein, which means more gluten when the flour is mixed with water. Soft wheat varieties have less protein and produce a more tender, delicate result.
- All-purpose flour is milled from hard wheat and sits at about 11.7% protein. It’s the workhorse flour designed to handle everything from cookies to pizza dough reasonably well.
- Bread flour also comes from hard wheat but has a higher protein content, around 12.7%, which creates the strong, elastic gluten network that gives bread its chewy structure.
- Pastry flour is milled from soft wheat at about 8% protein, producing the tender, crumbly texture you want in pie crusts, biscuits, and scones.
All of these are white flours made from the endosperm alone. The difference between them comes down to the wheat variety and its protein content, not the milling process itself.
What Gets Added Back
Because removing the bran and germ strips out most of the kernel’s vitamins and minerals, U.S. regulations require that standard enriched white flour have specific nutrients added back in. Each pound of enriched flour must contain 2.9 milligrams of thiamin (vitamin B1), 1.8 milligrams of riboflavin (vitamin B2), 24 milligrams of niacin (vitamin B3), 0.7 milligrams of folic acid, and 20 milligrams of iron. Calcium may also be added, up to 960 milligrams per pound.
Enrichment replaces some of what milling removes, but not everything. Fiber, for instance, is not added back, nor are the dozens of other micronutrients and beneficial plant compounds found in the bran and germ. This is why whole wheat flour is generally considered more nutritious, even though enriched white flour covers the key vitamins linked to deficiency diseases. The folic acid requirement alone, added to flour since 1998, has been credited with significantly reducing neural tube birth defects in the U.S.