Rate of Rise: What the Crash and the Flick Really Are

Roasting, In Practice · Part 2

Rate of rise is a useful reading. The crash and the flick are not defects, and there is no mechanism by which they could be. Chasing a smooth curve is chasing the shape of a graph.

01 What the number actually is

Rate of rise is a rate of change, not a measurement.

The software takes bean temperature, subtracts the reading from a moment ago, and divides by the interval. It is a derivative of another curve, which means every error in the original is amplified in it.

It depends heavily on your probe.

Probe thickness, how deep it sits in the bean mass, and how much the software smooths the signal all change the shape of the line. Two machines roasting the same coffee identically will draw different rate of rise curves.

What it is good for is comparison.

On one machine, with one probe and one setting, it tells you whether today's batch is moving like yesterday's. That is a real and valuable use.

02 The crash is not a defect

A crash means the rate of rise fell sharply, usually around first crack.

It is described in a great deal of roasting material as something to prevent at all costs, on the grounds that it ruins sweetness or flattens the cup.

The bean is still getting hotter throughout.

This is the part that gets skipped. A crash is a slowdown in the rate of increase. Temperature is still climbing. The beans are not cooling, and nothing is being reversed.

There is no chemistry that responds to the second derivative.

Reaction rates depend on temperature, time, moisture and the compounds present. No reaction in a coffee bean is sensitive to whether temperature is rising slightly faster or slightly slower than it was thirty seconds ago. A mechanism has never been proposed, let alone demonstrated.

What the crash does tell you is real.

It usually marks the moment the bean starts producing its own heat, or the moment your applied heat became insufficient for the mass in the drum. Those are worth knowing. They are not the same as a defect in the cup.

03 The flick is the same story

A flick is the small upturn that often follows a crash.

It is blamed for baked or hollow flavours in much the same way, and again without a proposed mechanism.

Much of it is the instrument rather than the bean.

A derivative computed from a lagging probe, then smoothed, will produce dips and rebounds on its own. Change the smoothing setting in the software and the flick can disappear from a roast you already finished.

The evidence has not appeared.

This idea has circulated for well over a decade in an industry full of people with roasters, probes and cupping tables. A controlled comparison showing that a flick alone degrades a cup has not been published. That absence is itself informative.

04 What to do with the reading instead

Use it as a signal about the machine, not a verdict on the coffee.

The curve is telling you about heat and mass. The cup is a separate question, answered by drinking it.

What you see	What it usually means	What to do
Sharp drop around first crack	The bean turned exothermic, or heat is short for the batch	Note it, taste the result, change nothing yet
Small rebound after the drop	Often the probe and the smoothing, not the bean	Compare with the same setting on the next batch
Curve reaching zero or going negative	The roast has genuinely stalled	This one matters, add heat or reduce the charge
Noisy line throughout	Probe placement or sampling interval	Fix the setup before reading anything into the shape

A stall is a real problem and worth separating from the rest.

If the rate reaches zero the bean temperature has stopped climbing, which means the roast is no longer progressing. That is a different event from a crash and the only one on this list that reliably shows up in the cup.

What would change this position.

A blind comparison of roasts matched on time, temperature and final colour, differing only in the shape of the rate curve, with tasters who did not see the graphs. If that work is done and the differences hold, the argument moves. Until then the smooth curve is an aesthetic preference presented as a rule.

First Penguin Coffee Company Roasting since 2010 and teaching roasting since 2016, from our production facility in Korea. Our coffees are listed under Beans in the top menu. Enquiries: 010-3444-1721

Next: development time ratio, what it describes and where it stops being useful.