What wheat specification should a flour mill contract for?

Moisture 12.5% max, protein at target ±0.3%, test weight 76 kg/hl min, falling number 250 s min, impurity 1.5% max including 0.5% foreign matter.

What is falling number?

A measure of alpha-amylase activity caused by sprouting in the ear. Below 250 s the starch is degraded and the flour produces sticky, gummy crumb. It cannot be corrected by milling or blending above about 20%.

Is test weight important?

Yes, as a proxy for soundness and expected extraction. Wheat below 74 kg/hl yields 2–4 points less flour and produces more bran per tonne.

Cluster article

Wheat Classes and Specifications: How to Write a Wheat Contract for a Flour Mill

Wheat classes by protein and hardness, the parameters that actually matter on a purchase contract, and the tolerance clauses that decide who pays when a load fails.

By Haiyun engineering desk Updated 2026-11-07 8 min read

Key takeaways

Contract on five parameters: moisture, protein, test weight, falling number, impurity. Everything else is noise.
Protein tolerance should be ±0.3% with pro-rata pricing outside it, not a pass/fail cliff.
Falling number below 200 s means sprout damage — reject, because no milling adjustment fixes it.

The five classes that matter commercially

Class	Protein	Hardness	Used for
Soft white / soft red	8.0–10.0%	Soft	Biscuit, cake, pastry
Hard red winter	11.0–12.5%	Hard	Pan bread, general bakery
Hard red spring	12.5–14.5%	Very hard	Hearth bread, strong flour, blending stock
Durum	12.5–14.5%	Very hard, vitreous	Semolina, pasta
Local feed / general	9.0–11.5%	Mixed	Steamed bread, flatbread, noodles

Local names vary by country — atta wheat, maida wheat, chakki wheat — but the underlying parameters are the same three: protein content, protein quality and hardness.

The five contract parameters

1. Moisture

Level	Consequence
Below 11.5%	Wheat is brittle; more broken kernels, lower extraction
12.0–13.0%	Ideal for milling and storage
13.0–14.0%	Acceptable short term; tempering water reduced accordingly
Above 14.0%	Mould risk; price must be adjusted on dry matter

Always price on dry matter, not wet weight. A 14% moisture load priced at the 12.5% rate gives the seller 1.7% extra wheat for free.

2. Protein

Measured by Kjeldahl (N × 5.7 for wheat) or NIR, expressed at 14% moisture basis.

Write the contract as target ±0.3% with pro-rata adjustment, not pass/fail. A cliff clause means a 0.1% shortfall rejects a whole truck, which costs everyone more than a price adjustment.

Clause form	Effect
“12.0% min, reject below”	Supplier ships 12.05%; you never see 12.5%
“12.0% ±0.3%, pro-rata”	Supplier targets 12.0%; you get consistency
“12.0–12.6% band, price by formula”	Best for blending operations

3. Test weight

76 kg/hl minimum for bread wheat, 74 for general purpose. Below 72 the wheat is likely shrivelled or heat-damaged and will underperform in the mill.

4. Falling number

250 s minimum. This is the one parameter with no recovery path.

Falling number	Meaning	Action
Above 300 s	Sound, dormant	Normal
250–300 s	Acceptable	Monitor
200–250 s	Mild sprout damage	Blend up to 20% max
Below 200 s	Significant sprout damage	Reject

Alpha-amylase from sprouting degrades starch into dextrins. Bread made from it has a sticky crumb that collapses. Milling cannot remove the enzyme because it is distributed throughout the endosperm.

5. Impurity

Fraction	Limit
Total impurities	1.5% max
Foreign matter (stones, metal, glass)	0.5% max
Other grain	1.0% max
Broken kernels	3.0% max
Ergots and sclerotia	0.05% max

Impurity above specification is a cleaning cost, not a milling cost. Every extra 1% of impurity is roughly 1% of intake capacity spent moving material you did not buy.

What is usually omitted and should not be

Parameter	Why it matters
Damaged kernels	Heat-damaged wheat produces dark specks in flour
Vitreousness	Affects roll settings and semolina yield
Pesticide residue	Regulatory compliance for export markets
Heavy metals	Cadmium limits in EU and Japan
Mycotoxins (DON)	1,250 ppb EU limit for unprocessed wheat

For export flour, DON and cadmium are the two that stop shipments.

Sampling: where contracts are won and lost

The contract means nothing without a sampling protocol.

Practice	Standard
Sampling method	Mechanical probe, 5–8 cores per truck
Sample division	Quartering or riffling, never hand-scoop
Reference sample	Retained, sealed, 500 g per lot, 90 days
Dispute resolution	Independent laboratory, cost to the losing party

Hand-scooping from the top of a truck samples the driest, cleanest wheat in the load. It is the single most common way buyers get cheated and the easiest thing to fix.