How often should millstones be dressed?

Every 300–500 operating hours. Hard wheat and continuous operation push toward 300; soft wheat and light duty toward 500.

What happens if I don't dress the stones?

The furrows round off and the stone smears grain instead of cutting it. Flour temperature rises above 45 °C, defeating the entire purpose of stone milling, and the flour darkens and coarsens.

Can I dress stones myself?

Yes with the right tools and training. Most mills have one technician trained for it. It takes 2–5 hours depending on stone size and condition.

Cluster article

Stone Dressing: Interval, Method and the Cost of Skipping It

How often stone millstones need dressing, what happens when they don't get it, the dressing method, and how to tell from flour temperature and colour that it is overdue.

By Haiyun engineering desk Updated 2026-11-07 6 min read

Key takeaways

Dress every 300–500 operating hours depending on wheat and load.
Undressed stones smear rather than cut — flour temperature rises and colour darkens.
The failure is gradual and invisible. Log stone temperature hourly and dress on schedule, not on symptoms.

Why dressing matters

A millstone is a cutting tool, not a grinding surface. Its face has furrows — grooves cut in a pattern from the centre to the edge — that shear grain as the stone turns.

Over time the furrows round off. The stone then rubs instead of cutting. The visible symptoms are subtle and the invisible ones are expensive.

Interval

Condition	Interval
Soft wheat, light load, <6 h/day	500 hours
Mixed wheat, 8 h/day	400 hours
Hard wheat, continuous	300 hours
Whole wheat, high bran load	250–300 hours
Flour temperature > 45 °C	Immediately
Visible flour colour darkening	Immediately

What goes wrong

Stage	Stone condition	Flour
0–200 h	Sharp furrows	Pale, cool, correct granulation
200–350 h	Slightly rounded	Slightly warmer, marginally coarser
350–500 h	Rounded	Warmer, darker, coarser
500–700 h	Polished	Hot, noticeably darker, uneven
> 700 h	Glazed	Burning smell possible, unacceptable

The critical point: there is no mechanical noise, no vibration, no alarm. The only signals are flour temperature, colour and granulation — all of which drift slowly enough that operators normalise them.

The temperature rule

Log stone surface temperature hourly.

Temperature	Status
Ambient + 5 to +12 °C	Normal, sharp stone
Ambient + 12 to +18 °C	Getting dull, plan dressing
Ambient + 18 to +25 °C	Dull, dress now
Above 45 °C absolute	Stop and dress immediately

A cheap infrared thermometer is the most valuable instrument in a stone mill.

Dressing method

Isolate and lock out the mill. Stones must not turn.
Remove the casing and expose the stone face.
Inspect the furrow pattern against the original template.
Re-cut the furrows with a dressing hammer and chisel, or a powered dressing tool for larger stones.
Level the face — high spots cause uneven wear and vibration.
Clean out all stone dust and chips before reassembly.
Run-in for 30–60 minutes with sacrificial grain, discarding the flour.
Verify temperature and granulation against baseline.

Time: 2–5 hours depending on stone size and condition.

Record keeping

Keep a stone log:

Field	Why
Date and hours since last dressing	Predicts next dressing
Wheat type and moisture	Explains wear rate variation
Stone temperature at start	Baseline
Furrow depth measurements	Objective wear metric
Operator	Accountability

Without a log, dressing happens when someone remembers. With a log, it happens on schedule and flour quality stops drifting.