From grain to bag: how wheat is milled and what extraction rate means

Introduction: flour starts as a living grain

Before a flour bag lands in your storeroom, the contents went through one of the most precise industrial separation processes in food manufacturing. Modern roller milling can split a single grain of wheat into more than twenty distinct streams, each with different protein content, ash content, and colour — then blend them back to exact specification.

Understanding that journey — from grain anatomy to extraction rate to T-type number — will change how you read a spec sheet, how you order flour, and how you troubleshoot inconsistencies in production. This article builds the foundation. The companion article Reading the flour spec sheet covers the tests used to verify quality.

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1. Anatomy of the wheat grain

Cross-section of a wheat kernel showing endosperm, bran layers, and germ with mass percentages

A wheat kernel is not uniform. It is three anatomically and chemically distinct zones, each of which has a different role in baking. [c45]

1.1 Endosperm — the flour zone

The starchy endosperm makes up approximately 83% of the kernel by weight. [c45] It contains:

• Starch: approximately 70–75% of its dry weight — the carbohydrate substrate that ferments under yeast and gelatinises in the oven to set bread structure. [c46]
• Protein: approximately 8–15% — specifically the storage proteins gliadin and glutenin, which combine with water and mechanical work to form the gluten network. [c46]
• Minor amounts of fat, moisture, and enzymes.

The inner endosperm (furthest from the bran) is the palest, starchiest, and lowest in protein. The outer endosperm, closest to the bran, is richer in protein. This is why high-extraction flours tend to have both more ash and more protein than low-extraction patent flours — they include more of the outer endosperm layers.

1.2 Bran — the fibre zone

The bran layers — pericarp, testa, and aleurone cell layer — make up approximately 14% of the kernel. [c45] The bran is rich in:

• Dietary fibre (arabinoxylan, cellulose, beta-glucan in the aleurone)
• Minerals (phosphates, potassium, magnesium — these are the ash measured in the T-type system)
• B-vitamins (thiamin, riboflavin, niacin — concentrated in the aleurone layer)
• Phytic acid — reduces mineral bioavailability, though sourdough fermentation partially degrades it [c47]

The aleurone is a single-cell-thick layer at the boundary between bran and endosperm. It is biochemically active and contains much of the grain's B-vitamin reserves. Because of its position, it may partially blend into the flour during stone milling, giving stoneground flour a different nutritional character than roller-milled flour of the same T-type. [c47]

Bran's effect on gluten: Even small quantities of bran particles in flour physically cut the gluten network during mixing. This is why high-extraction flours tend to produce denser, more open crumbs than white flour — the bran interrupts gluten strand formation. In practice, you can compensate by mixing slightly longer, increasing hydration, or adding a small quantity of vital wheat gluten.

1.3 Germ — the fat zone

The embryo (germ) makes up approximately 3% of the kernel. [c45] It contains:

• Unsaturated fats (~10% of germ weight) — provides flavour but causes rancidity in storage [c47]
• Vitamin E (tocopherol) — a natural antioxidant
• B-vitamins and various enzymes, including lipases

Modern roller mills deliberately flatten and sieve out the germ to prevent rancidity — this is why white flour lasts 5 months while stone-ground wholemeal is typically sold with a 3–6 month shelf life. [c47] The Doves Farm BIOBAKE Organic Strong Wholemeal uses a roller mill (stated on spec sheet) and achieves a 6-month shelf life by limiting oil-bearing germ fragments. [c41]

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2. The milling process

Flow diagram of roller mill wheat milling stages: cleaning, tempering, break rolls, sifting, reduction rolls, flour streams

2.1 Cleaning

Incoming wheat is cleaned mechanically before any milling begins. Stoning removes rocks and dense impurities; aspiration removes dust and light chaff; magnetic separators remove metal. This is why the spec sheets for all reviewed products specify inorganic impurity content as zero (niedopuszczalna/none). [c1, c8]

2.2 Tempering (conditioning)

Cleaned wheat is wetted with water and rested for 8–24 hours before milling. [c49] Tempering serves two purposes:

1. Toughens the bran — hydrated bran becomes leathery and flexible, allowing the break rolls to shear it open without grinding it into powder that would contaminate the flour.
2. Softens the endosperm — moist starch grinds more easily to a fine powder with lower energy input.

The moisture added in tempering is one reason why flour specification sheets set a maximum moisture of 15% rather than specifying the exact post-tempering level — the miller controls this to achieve clean separation, not to a fixed number. [c12]

2.3 Break rolls — opening the grain

Diagram of corrugated break rolls and smooth reduction rolls with particle flow and sifting between passes

The tempered wheat first passes between pairs of corrugated (fluted) break rolls running at different speeds. The speed differential creates a shearing action that tears the grain open lengthwise along the crease, releasing endosperm as coarse semolina while leaving the bran as large flakes. [c50]

Typically 4–5 break roll passes progressively extract endosperm from the bran and germ. After each pass, the material passes through a plansifter (vibrating sieve stacks) that separates particles by size.

2.4 Purification and reduction

The coarse semolina particles (endosperm chunks) separated by the plansifter are fed to purifiers — air classifiers that blow light bran-contaminated particles off the surface of semolina streams. This produces clean semolina for the next stage.

The purified semolina then passes through smooth reduction rolls that progressively grind it to fine flour. Each reduction pass grinds the particles finer; sifting follows each pass. The result is a series of flour streams with slightly different characteristics — earlier (purer) streams have lower ash and higher starch; later streams progressively include more from the outer endosperm and any residual bran. [c48, c50]

2.5 Flour streams and blending

A commercial roller mill may produce 20 or more distinct flour streams. These are analysed for ash content, protein, and colour, then blended to hit a target specification — typically an ash range corresponding to a specific T-type. The miller does not simply take all streams and mix them; the blend recipe is adjusted seasonally as the wheat supply changes. [c48]

What this means for bakers: Two bags of T550 from the same mill but different harvest years may require slightly different hydration. The spec sheet sets the minimum/maximum guardrails; the mill targets a typical value within that window. This is why GoodMills specifies ash as a range (0.51–0.58%) rather than a single number — the range reflects blending precision across seasons, not poor quality control. [c8]

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3. Extraction rate — the single most important milling concept

Diagram showing three extraction levels — patent/white, high-extraction, and wholemeal — as proportions of the wheat kernel cross-section

Extraction rate is defined as the mass of flour produced per 100 kg of cleaned wheat grain input, expressed as a percentage. [c52]

Extraction rate (%) = (kg of flour produced / kg of clean wheat) × 100

3.1 What different extraction rates produce

Standard white flour is produced at approximately 72–78% extraction. At this level, most of the bran and germ have been removed, and the flour is composed almost entirely of endosperm material. [c52]

A small fraction of the grain — bran, germ, and the coarser endosperm particles that resist fine grinding — goes to by-products: bran for animal feed or fibre supplements, and germ for oil pressing. [c51]

Wholemeal or whole-grain flour at approximately 95–100% extraction retains everything — endosperm, bran, and germ are all ground together and remain in the flour. Nothing is sieved away. [c52]

In between lies a continuous spectrum. A T750 flour at approximately 78–82% extraction retains slightly more of the outer endosperm and some fine bran particles compared to T550, giving it more colour, more fibre, and more mineral content. [c53]

3.2 The flour fraction taxonomy

Three traditional terms describe different extraction levels within the milling process: [c51]

| Term | What it means | Approx. extraction | Ash approx. | |---|---|---|---| | Patent flour | Purest fraction — centre of endosperm only; first, cleanest streams | 40–60% | 0.3–0.45% | | Straight flour | All flour streams combined (standard commercial white flour) | 72–78% | 0.4–0.65% | | Clear flour | Dark residual streams after patent flour removed; high in protein and ash | Residual fraction | 0.7–1.5%+ |

In the Polish and European T-type system, white bread flour (T550) corresponds approximately to straight flour; T450 is closer to a strong patent grade. Clear flour is rarely sold directly but is used in rye bread and some speciality dark breads where the darker colour and stronger flavour are desired. [c51]

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4. The T-type system — ash encodes extraction rate

The insight that makes the T-type system elegant is that ash content directly reflects how much bran is in the flour — and bran mineral content is consistent enough that a single ash measurement captures the extraction level accurately. [c55]

The Polish (and broadly European) convention: the type number equals the ash content in milligrams per 100 grams of dry flour. [c55]

• T450 = approximately 450 mg ash / 100 g dry flour = approximately 0.45% ash
• T550 = approximately 550 mg ash / 100 g dry flour = approximately 0.55% ash
• T750 = approximately 750 mg ash / 100 g dry flour = approximately 0.75% ash
• T2000 = approximately 2000 mg ash / 100 g dry flour = approximately 2.0% ash

The spec sheets confirm this directly: GoodMills T550 specifies ash 0.51–0.58% d.m.; the Wągrowiec Mill T450 specifies ash max 0.48% d.m. [c1, c8]

4.1 What rising ash content means in the bakery

As extraction rises and ash rises, three things happen simultaneously: [c53]

1. Colour darkens — from brilliant white (T450) to buff (T750–T850) to grey-brown (T2000 wholemeal rye). Seven flour samples in white ramekins showing colour gradient from T450 bright white to T2000 dark grey-brown

2. Fibre increases — the bran fraction carries most of the grain's dietary fibre. The nutritional data from the Domson catalogue spec sheets confirms this: T450 has approximately 2.5g fibre/100g; T2000 wholemeal rye has 14.4g fibre/100g. [c4, c28] (Values from nutritional information panels on spec sheets — typical values, not specification limits.)

3. Flavour intensifies — bran contributes earthy, nutty, and slightly bitter notes. This is desirable in rustic bread and sourdough but inappropriate in fine pastry or sponge cake.

4.2 International classification crosswalk

The T-type numbering convention is shared across Poland, France, and broadly across continental Europe — but boundary values differ between national systems. [c57] The table below is a comparative guide, not a precise equivalence:

| Polish T-type | French T-type | German Weizenmehl | Italian Tipo | Approx. use | |---|---|---|---|---| | T450 | T45 | W405 | Tipo 00 | Pastry, pasta | | T500–T550 | T55–T65 | W550 | Tipo 0–1 | White bread, rolls | | T750 | T80 | W812 | Tipo 1 | Rustic bread | | T850–T1050 | T110 | W1050 | Tipo 2 | Brown bread | | T1850 (Graham) | — | W1600 | Integrale | Wholegrain loaves | | T2000 (Wholemeal rye) | — | — | — | Wholemeal rye |

Note (medium-reliability crosswalk): This table is drawn from trade literature. The French T-type and Polish T-type share the same convention; German and Italian systems use different exact boundaries. Use this table as a starting guide when substituting imported flour for a local grade — always verify the ash content on the incoming spec sheet rather than trusting the type number alone, since naming conventions between suppliers can vary. [c57]

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5. Spec sheet data for Domson catalogue flours

The following parameters were read directly from supplier specification documents for thirteen products in the Domson catalogue. See [table-domson-spec-comparison] for the complete side-by-side table.

5.1 Wheat flours — Polish classification

Wheat Flour Type 450 (Wągrowiec Mill): ash max 0.48% d.m.; wet gluten min 23%; protein min 8.0%; Hagberg Falling Number min 220 s; moisture max 15%; shelf life 5 months; country of origin Poland. Allergen: GLUTEN. [c1–c4]

Domson White Flour Type 500 (Wągrowiec Mill): ash max 0.52% d.m.; wet gluten min 23%; protein min 8.0%; FN min 220 s; moisture max 15%. Allergen: GLUTEN. [c5–c7]

Domson Wheat Flour T550 — GoodMills Fortified (GoodMills Polska): ash 0.51– 0.58% d.m. (a range reflecting seasonal grain variation); wet gluten 28–32%; protein 11.5–12.5%; FN min 220 s; gluten index 75–99; moisture max 15%; storage at relative humidity max 75%. Fortification (voluntary, matching UK BFR 1998 levels): calcium carbonate 235–390 mg/100g, iron ≥ 1.65 mg/100g, thiamin ≥ 0.24 mg/100g, nicotinic acid ≥ 1.60 mg/100g. [c8–c13]

FOOD SAFETY NOTE: The GoodMills T550 fortification matches UK Bread and Flour Regulations 1998 minimums. This fortification is VOLUNTARY in the Polish and EU context — it is NOT mandated by Polish or EU law for T550 flour. Do not assume other T550 products are fortified to the same levels. Allergen: GLUTEN. [c59, c60]

Komplexmłyn Wheat Flour T550 (Wągrowiec Mill): ash max 0.58% d.m.; wet gluten min 25%; FN min 220 s. An alternative T550 option at a lower specified protein minimum — appropriate for standard production where cost per kg is a priority over the consistently high protein of the GoodMills fortified grade. Allergen: GLUTEN. [c14]

Domson Bread Flour Type 750 (Wągrowiec Mill): ash max 0.82% d.m.; wet gluten min 26%; protein min 10% (typical 11.6g/100g per nutritional panel); FN min 220 s; fibre 2.9g/100g. The higher ash brings deeper flavour suitable for rustic and artisan breads. Allergen: GLUTEN. [c15–c18]

Wheat Flour Type 850 (Wągrowiec Mill): ash max 0.90% d.m.; wet gluten min 26%; FN min 220 s. A brown bread flour where the closer-to-bran extraction contributes colour and fibre without the weight of full wholemeal. Allergen: GLUTEN. [c19–c21]

Graham Wheat Flour Type 1850 (GoodMills Polska): ash max 2.0% d.m.; FN min 180 s; moisture max 15%; protein 12.3g/100g (nutritional panel); fibre 12.3g/100g. The lower FN minimum (180 s vs 220 s for white wheat flour) reflects the practical reality that grain milled at such high extraction typically includes bran-associated amylase activity. [c42–c44]

FOOD SAFETY NOTE (HUMAN REVIEW REQUIRED): Graham T1850 spec sheet specifies GoodMills internal mycotoxin limits: aflatoxins B1 ≤ 2 µg/kg; total aflatoxins ≤ 4 µg/kg; ochratoxins ≤ 3 µg/kg; zearalenone ≤ 75 µg/kg; deoxynivalenol (DON) ≤ 750 µg/kg; ergot alkaloids ≤ 150 µg/kg. DON, ZON, aflatoxin, and ochratoxin limits match EU legal maxima (EC Reg 1881/2006 and amendments). The ergot alkaloid limit of 150 µg/kg is a GoodMills internal supplier limit — it is more conservative than the EU legal maximum of 500 µg/kg for cereal flour (EU Reg 2023/915); the EU legal maximum is NOT 150 µg/kg. A food safety specialist must review and confirm all cited limits against current EU regulations before publication. Allergen: GLUTEN. [c44]

5.2 Rye flours

Rye Flour Type 720 (GoodMills Polska): ash max 0.78% d.m.; FN min 90 s (see note); moisture max 15%; colour white-grey; protein 6.5g/100g, fibre 7.4g/100g. This is the standard light rye flour for mixed-grain bread and rye rolls. Allergen: GLUTEN. [c22–c25]

Wholemeal Rye Flour Type 2000 (GoodMills Polska): ash max 2.0% d.m.; FN min 90 s; moisture max 15%; colour white-grey with bran; protein 8.4g/100g, fibre 14.4g/100g — nearly twice the fibre of rye T720. Used for dense sourdough rye breads and pumpernickel. Allergen: GLUTEN. [c26–c29]

Note on rye Falling Number: The GoodMills commercial specification floor of > 90 s is a minimum to exclude severely sprouted grain. Rye starch gelatinises at a lower temperature than wheat starch, and rye amylases are more heat-stable, so rye FN values are structurally lower than wheat FN values and cannot be compared on the same scale. For sourdough rye applications, a FN above 120 s is generally preferable to minimise sticky, collapsing crumb. Confirm with your GoodMills representative if rye FN is critical to your process.

5.3 UK wheat flours

Windrush Strong White Bread Flour (Matthews Cotswold Flour, 16 kg): protein 12.0–12.5% (target 12.2%); FN 250–400 s (target 350 s); water absorption 55–61% (target 58%); moisture 13.5–15%; fortified per UK Bread and Flour Regulations 1998 (Creta Plus chalk 0.31%, vital wheat gluten added < 1.5%). Origin: Germany or UK wheat. Allergen: GLUTEN (cereals containing gluten); potential soya contamination risk in supply chain (noted on spec sheet). [c33–c35]

The Windrush Strong White falls squarely in the optimal breadmaking window for Falling Number (250–400 s, target 350 s) — a much tighter and higher target than the minimum-only Polish specifications. This reflects UK milling practice where premium bread flour is specified more tightly for consistent automated production.

5.4 Spelt flours

Stoneground White Spelt Flour (Matthews Cotswold Flour, 16 kg): protein 9.0–13.0% (target 11.0%); FN min 220 s; water absorption 53–65% (wide range — reflects spelt's variable and fragile gluten hydration); no additives; UK origin only. Allergen: GLUTEN (SPELT WHEAT). [c36, c37, c61]

FOOD SAFETY NOTE — ALLERGEN LABELLING (HUMAN REVIEW REQUIRED): Both Matthews and Doves Farm spec sheets declare spelt as 'GLUTEN (SPELT WHEAT)', and all practical guidance is to declare spelt by name in ingredients lists with the allergen emphasis. However, the precise legal basis under EU Regulation 1169/2011 Annex II requires specialist review before publication: Annex II lists spelt parenthetically within the wheat category ('wheat (such as spelt...)') rather than as a separately enumerated entry. The practical labelling obligation — declare as 'SPELT WHEAT' or 'SPELT (WHEAT)' and emphasise the allergen — is the correct advice and is consistent with FSA guidance, but the article's reference to spelt being 'named separately' in Annex II should be verified by a food law specialist before publication. [c37, c61]

Wholemeal Spelt Flour (Doves Farm Foods, 25 kg): protein min 11.8% (range 11.8–17.0%); moisture 11.5–14.5%; stoneground; E.coli < 10/g; Salmonella absent. Allergen: GLUTEN (SPELT WHEAT). [c38, c39]

5.5 Oat flour

Oat Flour (Agrol, 25 kg): moisture max 11% (tighter than wheat — oat lipids are at risk of rancidity at higher moisture); protein 13g/100g; fibre 10.3g/100g; fat 7.9g/100g (high compared to wheat flour — from oat lipids); colour grey-white; produced by hydrothermally treating and flaking oats then roll-grinding. [c30, c31]

FOOD SAFETY NOTE — ALLERGEN: The Agrol Oat Flour spec sheet explicitly declares a gluten cross-contamination risk from the agricultural and processing environment. Oats are classified as a gluten-containing cereal under EU Regulation 1169/2011 and equivalent UK law. Do not use this flour in gluten-free products and declare GLUTEN on all downstream products containing this ingredient. [c32, c60]

Organic Strong Wholemeal Bread Flour (Doves Farm Foods, 25 kg): protein 12.6g/100g; fibre 11.2g/100g; fat 2.5g/100g; energy 311 kcal/100g; roller milled; Soil Association and Kosher certified. Allergen: GLUTEN. [c40, c41]

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6. Roller milling versus stone milling

Both production methods appear in the Domson catalogue. Their practical differences for bakers are summarised in [table-milling-methods].

The essential distinction: roller milling achieves clean, controlled separation of bran and endosperm, giving very consistent colour and ash. Stone milling grinds everything together in a single pass, retaining germ oils and aleurone material, giving more complex flavour at the cost of shorter shelf life and more variable absorption.

The Matthews Stoneground White Spelt Flour and the Doves Farm Wholemeal Spelt Flour are stoneground (stated on their spec sheets). All GoodMills and Wągrowiec Mill flours are roller-milled; the Doves Farm BIOBAKE Organic Wholemeal is also roller-milled (stated on spec sheet). [c41]

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7. Choosing the right flour type: a practical guide

7.1 Match the T-type to the product

| Product type | Recommended T-type | Key reason | |---|---|---| | Fine pastry, shortcrust, delicate sponge | T400–T450 | Neutral flavour; white colour; low fibre interference with fat/sugar structure | | Layer cakes, all-purpose baking, soft rolls | T500 | Versatile; slight cream colour acceptable | | White sandwich bread, pizza, rolls | T550 | Standard European white bread flour; GoodMills high-protein grade for sourdough | | Rustic, artisan, sourdough breads | T750–T850 | More mineral flavour; extra protein in outer endosperm; better fermentation | | Graham bread, wholegrain loaves | T1850 | Significant bran content — declare fibre on label; adjust hydration up 5–10% | | 100% wholemeal bread, pumpernickel | T2000 (rye) | Full grain; dense; requires sourdough or long fermentation to manage texture | | Mixed-grain and rye bread | Rye T720 + T550 blend | Light rye character without structural compromise; classic 60/40 or 80/20 blend |

7.2 Adjust hydration for T-type

Higher extraction flours absorb more water because bran particles absorb water at approximately 3–4 times the rate of pure endosperm starch. As a practical rule, every step up in T-type (e.g. T550 → T750) requires an increase of approximately 3–5% additional water in your recipe to maintain the same dough consistency. The GoodMills Graham T1850 nutritional spec (12.3g fibre, 2.0g fat, 12.3g protein per 100g) suggests substantially higher absorption than T550 — expect to add 8–12% more water compared to a T550 recipe baseline. [c43]

(Single-source absorption estimate from practitioner convention; verify with your specific flour and dough consistency target before committing to production.)

7.3 Fermentation considerations

Higher-extraction flours generally ferment more vigorously because:

1. More minerals (from bran) support yeast activity and sourdough bacteria.
2. More enzymes remain active (bran-associated lipases and amylases).
3. Higher fibre can accelerate organic acid production in sourdough.

For sourdough production using T750 or T850, reduce bulk fermentation time by 10–20% compared to T550 baseline, or reduce dough temperature by 1–2°C to slow fermentation. Monitor the dough rather than relying on fixed timers.

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8. What the spec sheet does not tell you

The spec sheets reviewed across thirteen products contain excellent primary data on ash, moisture, protein, wet gluten, and falling number. However, no Polish flour spec sheet in this set reports:

• Alveograph W and P/L values — dough strength and extensibility (standard in French and Italian milling; request from GoodMills or Wągrowiec Mill for automated line setup)
• Zeleny sedimentation index — gluten quality beyond protein quantity (useful for sourdough and high-hydration work; request from supplier)
• Farinograph DDT and stability — mixing time and dough tolerance (useful for setting mixer parameters; request from supplier)
• Starch damage % — relevant for high-absorption applications and rye specialities

These parameters are covered in the companion article [A1-key-quality-parameters]. If any of them are critical to your process, request the supplementary technical data sheet from your supplier contact — most commercial mills have this data internally even if it is not printed on the standard spec sheet.

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Coverage notes and gaps

Solid: Grain anatomy and roller milling process confirmed from two independent academic open-text sources plus UK Flour Millers trade body. Extraction rate and T-type ash relationship confirmed from three independent sources. Spec-sheet parameters (ash, moisture, FN, wet gluten, protein, allergens) extracted from thirteen supplier PDFs and cited at claim level.

Single-source figures (confidence: medium): Grain anatomy percentages (endosperm 83%, bran 14%, germ 3%) appear consistently in both academic sources but vary slightly by wheat variety. The 3–5% hydration adjustment per T-type step is practitioner convention; no independent numerical confirmation was available in sources read. Rye FN minimum 90 s (GoodMills spec floor) — academic literature suggests optimal baking FN is higher; present the floor as a minimum not a target.

Gap: No spec sheet in this set reports Zeleny, alveograph, or farinograph data — these are standard in French and Italian milling but not in the Polish market. Schedule the companion article A1-key-quality-parameters (already drafted) as the mandatory read for anyone needing those parameters.

Follow-up recommended: The GoodMills T550 fortification crosswalk to UK BFR 1998 was verified by comparing spec-sheet values to the UK Flour Millers publication. Consider confirming directly with GoodMills customer service whether this is a permanent standard or a batch-by-batch option, as the spec sheet notes seasonal variation.