Wheat Tempering: Moisture Targets, Time and Why ±0.2% Matters

Why temper at all

Dry wheat is a composite of brittle bran and hard endosperm. If you mill it dry:

• The bran shatters into fine powder that contaminates the flour
• The endosperm is difficult to reduce cleanly
• Ash rises sharply and extraction falls

Tempering adds water until the bran becomes leathery and tough, while the endosperm becomes softer and more friable. The bran then peels off in flakes rather than shattering, and the endosperm grinds cleanly.

Target moisture by wheat class

Wheat class	Target tempered moisture	Tempering time
Soft wheat (biscuit, cake)	15.0–15.5%	12–16 h
Medium wheat (noodle)	15.5–16.0%	16–20 h
Hard wheat (bread)	16.0–16.5%	18–24 h
Durum (pasta)	16.5–17.0%	18–24 h

These are starting points. Every wheat origin behaves slightly differently, and the correct target is the one that produces the lowest ash at the highest extraction on your specific mill.

The time factor

Water penetration is not instantaneous. It moves through the bran layers and into the endosperm over hours.

Time	State
0–4 h	Surface water only; crease dry
4–8 h	Bran hydrated, endosperm still hard
8–12 h	Water reaching endosperm; usable but marginal
12–18 h	Full hydration; good
18–24 h	Optimal for hard wheat
> 30 h	Risk of microbial growth and sprout damage

Below twelve hours, the crease stays dry and the bran remains brittle at the crease — which is exactly where most bran contamination originates.

Temperature

Water diffuses faster at higher temperature. At 25–30 °C, full hydration takes roughly 14 hours. At 10 °C, it takes 24–30 hours.

In cold climates, either extend the tempering time or warm the wheat. Warming 10 °C above ambient typically halves the required time.

Warning: warming above 35 °C risks microbial growth and changes gluten behaviour. Stay below that.

Manual versus automatic

Manual water addition — an operator with a flow meter and a moisture reading — varies by ±1.5% between operators and between shifts.

Automatic microwave-controlled dampening holds ±0.2%.

The consequence of the difference is visible in the mill:

Tempered moisture variation	Effect on ash	Effect on extraction
±0.2% (automatic)	Baseline	Baseline
±0.7% (careful manual)	+0.03 points	−0.5 points
±1.5% (typical manual)	+0.08 points	−1.5 points

At 60 t/d, 1.5 points of extraction is roughly 0.9 t of flour per day — USD 360/day, USD 118,000 a year.

An automatic dampening system costs USD 12,000–25,000. It pays back in under three months.

Multi-wheat blending

If you blend wheat origins, each origin needs its own moisture target. Blending wheat at different moistures produces uneven tempering that no single dampener setting can fix.

Solutions:

• Temper separately: separate bins per origin, each with its own water addition, blended after tempering
• Blend before tempering: proportional blending at intake, then single tempering — simpler but less precise
• Electronic proportioning scales + multiple bins: the industrial standard above 100 t/d

Practical checks

1. Calibrate the dampener monthly against an oven-dry reference. A drifted sensor is worse than no sensor because operators trust it.
2. Sample from the bin outlet, not the inlet. Inlet moisture tells you what you added; outlet moisture tells you what the mill will see.
3. Check for surface water. Free water on kernels means over-addition; the wheat will smear on the rolls.
4. Log tempering time per bin. Rotation discipline matters more than any instrument.
5. Watch for sprout damage if tempering exceeds 30 hours, especially in warm weather.