The shift from stone to roller milling in the late 19th century was driven by economics, not nutrition. Roller mills could process more grain per hour, produced white flour with a 12–18 month shelf life, and required less skilled labour once mechanized. The trade-offs in nutritional composition were understood at the time but considered secondary to the commercial and logistical advantages of the new system.
The contemporary interest in stone-milled flour is, in part, a response to those trade-offs. This article documents how stone milling works, what it preserves in the grain, and how the resulting flour behaves differently from roller-milled equivalents.
Technical milling data referenced below is drawn from the American Association of Cereal Chemists International (AACCI) and the Cereals & Grains Association, and from published data by Canadian Grain Commission quality assessments.
What Roller Milling Does
Roller milling, perfected in the 1870s using Hungarian technology and subsequently adopted across North America and Europe, separates the three anatomical components of a wheat kernel: the endosperm (starchy interior), the bran (outer layers), and the germ (embryo). This separation is achieved by passing grain through a sequence of corrugated and smooth steel rollers at progressively closer tolerances.
The endosperm is reduced to fine white flour — largely starch and protein (gluten-forming), with minimal fat. The bran and germ are removed as byproducts, sold separately or incorporated into animal feed. The resulting white flour is stable at room temperature for over a year because the oils present in the germ — which cause rancidity — have been removed.
Modern roller mills also generate heat during processing. Grain temperature in commercial roller mills can reach 40–60°C at the point of grinding, depending on throughput and roller gap settings. At these temperatures, some heat-sensitive compounds in the grain — certain B vitamins, enzymes, and fatty acids — are reduced. This is compensated in commercial flour production through mandated fortification (Canada's Food and Drug Regulations require that enriched flour contain specified minimum levels of thiamine, riboflavin, niacin, folic acid, and iron).
What Stone Milling Does
Stone milling does not fractionate the grain. The whole kernel is passed between two stone faces — traditionally granite, now often engineered composite stone — that rotate at low speed (80–200 RPM in most artisan mills). The result is a flour that contains all three anatomical components: endosperm, bran, and germ, distributed unevenly through the flour mass.
Because the germ is included, stone-milled flour contains the grain's natural oils. These oils are responsible for the richer flavour of whole grain flour and for its shorter shelf life. Properly stored stone-milled whole grain flour has a practical shelf life of 2–4 weeks at room temperature, 3–6 months refrigerated, and up to a year frozen.
Temperature During Stone Grinding
Stone mills operating at standard artisan speeds generate significantly less heat than roller mills — grain temperature rarely exceeds 25–30°C during milling, often remaining close to ambient temperature. This is the basis of the claim, commonly made by artisan millers, that stone milling is "cold" milling, though the descriptor is relative rather than absolute.
The lower heat exposure is relevant to enzyme activity. Wheat grain contains amylases, proteases, and lipases that contribute to flavour development during fermentation. At temperatures above approximately 35–40°C, some of these enzymes lose activity. Stone-milled flour, milled closer to ambient temperature, retains more enzymatic activity — which has practical implications for sourdough fermentation, where enzyme activity drives flavour complexity.
Extraction Rate and Flour Type
Extraction rate refers to the percentage of the grain mass that ends up in the final flour. Roller mills producing standard white flour operate at an extraction rate of roughly 72–75% — that is, 72–75% of the grain by weight becomes white flour, and the remaining 25–28% (bran and germ) is separated out.
Stone mills producing whole grain flour operate at 100% extraction — nothing is removed. However, stone mills can also be adjusted to sift out portions of the bran after milling, producing what is called high-extraction flour (typically 80–90% extraction). High-extraction flour is lighter than whole grain flour but darker than white flour, and retains more of the bran and germ fraction than commercial whole wheat flour produced by roller mills (which typically adds back bran to white flour rather than retaining it from the start).
Why Extraction Rate Matters for Baking
Higher extraction flours contain more bran particles, which physically interrupt gluten network formation. This is why whole grain bread is denser than white bread: bran cuts gluten strands during mixing, limiting the extensibility of the dough. Bakers working with high-extraction stone-milled flours often use longer autolyse periods (pre-mixing rests before salt is added) and gentler mixing to develop gluten without excessive bran cutting.
The germ oil fraction also affects gluten. Wheat germ oil contains lipases that, when active, can oxidize glutenins and gliadins, affecting dough extensibility. In freshly milled whole grain flour this effect is detectable; it is one reason bakers sometimes allow freshly milled flour to rest for 24–72 hours before use.
Canadian Artisan Stone Mills
Stone milling at an artisan scale in Canada uses two main equipment categories: traditional millstone pairs (granite or engineered stone) and high-speed impact mills (also called centrifugal mills). The latter operate differently from millstones — grain is propelled against a fixed surface at high speed — and can achieve finer particle size but generate more heat and are generally not considered equivalent to millstone grinding by most artisan flour producers.
Mills confirmed to use traditional stone or composite millstone technology in Canada as of 2024:
- Speerville Flour Mill, Speerville, New Brunswick — Austrian millstones, operating since 1983
- Flourist, Vancouver, BC — Austrian Osttiroler mill
- Brodflour, Toronto, Ontario — Meadows stone mill
- Highwood Crossing Foods, Aldersyde, Alberta — stone-milled certified organic flours
- La Milanaise, Milan, Quebec — operates at larger scale with stone milling for specialty flours
Shelf Life and Storage Practicalities
The practical consequence of retaining the germ in stone-milled flour is reduced shelf life. Germ oils, particularly linoleic acid (an omega-6 fatty acid), oxidize readily at room temperature. Oxidation produces compounds that smell and taste rancid — a process detectable in whole grain flour stored at 20°C for more than 3–4 weeks in warm months.
Purchasing stone-milled flour in smaller quantities (1–2 kg at a time) and storing it in an airtight container in the refrigerator is the standard recommendation. Many Canadian artisan millers mill to order or in small weekly batches, and note the mill date on packaging so buyers know the flour's age.
For detail on how specific heritage grain varieties perform in stone milling, including protein content and flour behaviour comparisons, see the einkorn, emmer, and spelt comparison article.
Summary of Key Differences
- Extraction: Stone milling typically 100% (whole grain) or 80–90% (high-extraction); roller milling typically 72–75% for white flour
- Temperature: Stone milling 20–30°C; roller milling 40–60°C at point of contact
- Components retained: Stone milling retains bran, germ, and endosperm; roller milling removes bran and germ
- Shelf life: Stone-milled whole grain flour 2–4 weeks at room temperature; roller-milled white flour 12–18 months
- Enzyme activity: Higher in stone-milled flour due to lower milling temperature
- Flavour: Richer and more complex in stone-milled whole grain flour due to germ oil and bran compounds