Milling

Milling is not grinding a berry into powder and calling it done. A wheat kernel is bran (outer layers), endosperm (the starchy interior that becomes white flour), and germ. Roller milling opens that kernel on purpose so those parts can be sieved apart and later blended — or not.

Break, reduction, streams #

USDA’s Soft Wheat Quality Laboratory describes a mill that is meant to resemble commercial flow: corrugated break rolls open the kernel; smooth reduction rolls reduce the freed endosperm (middlings) toward flour; sifters decide which particles continue and which leave as bran or shorts ¹. Moisture is adjusted first. On that experimental mill, soft red winter wheat is tempered to 14.0% moisture and held at least 24 hours so water can move through the grain before the first break ¹. Tempering is a mill-floor lever, not a bakery recipe step.

Straight-grade flour is a blend of streams, not a mystic grade. In the same USDA description it is ten streams (break flours, reduction flours, plus grader and duster flour), typically about 50 microns, with ash usually between 0.42% and 0.52%, and flour yields of 70% to 78% depending on variety and grain condition ¹. Bran, shorts, and red dog are the leftovers of that choice. Higher extraction keeps more of the kernel — more yield, more bran specks, usually more ash.

Why ash is on the spec sheet #

Ash is not flavor. USDA measures flour ash by AACC Method 08-01 as the inorganic residue after combustion. Because those minerals are more concentrated in bran than in endosperm, ash is an indirect indicator of residual bran in the flour ². A baker who only reads protein is missing the mill’s cleanliness story. Calvel treats ash alongside gluten and enzymes as flour behavior, not a single number to worship ³.

U.S. names for the bag — flour, bread flour, whole wheat flour — are identity standards in 21 CFR Part 137, not mill-brand poetry ⁴. Whole wheat, in that legal sense, is a decision to keep the kernel’s parts in the food. White flour is a decision to leave most of the bran and germ behind.

What to notice #

Look. White flour should be even; bran specks tell you extraction or a whole-wheat blend. Whole-wheat flour that looks like pale dust with a few flakes is not the same product as flour that is brown throughout.

Feel. Particle size changes absorption and how fast the dough comes together. A very fine whole wheat still carries bran; it is not white flour with extra fiber sprinkled on.

Smell. Freshly milled whole grain can smell sweet and wheaty. Rancid germ oil smells like old nuts. That is a mill-and-storage problem, not a starter problem.

Variables #

Wheat class and condition (shriveled or sprouted grain mills poorly ¹), tempering, roll gaps, which streams you keep, and whether the mill stones a whole berry or rolls and sifts. Home “milling” a berry in a blender is particle-size reduction without a stream map. Do not treat it as the same process.

Failure modes #

• Specky, high-ash white flour. Streams that should have been shorts made it into the bag. Quality, not a sourdough defect.
• Gray, tight dough from “strong” flour that still feels dead. Protein without the mill’s other specs — ash, falling number, enzyme — is an incomplete story. See Gluten for the network; this page is how the powder was made.
• Assuming the nearest mill is a farm. A processor can mill, blend, and wholesale grain it did not grow. Giusto's Vita-Grain is that kind of Bay Area node.

Application: Wheat flour. A bakery that publishes a flour story, such as Acme Bread Company, is downstream of this page. Sourdough is one craft that has to live with whatever the mill shipped.