The Man Who Named the Crash Says Your Probe Is Too Thick

Roasting, In Practice

The roaster who named the crash also advises using a thinner bean probe before forming strong opinions about how crashy your curves look. Both statements cannot be load-bearing at once.

01 State the claim fairly first

The position is well known and clearly argued.

Scott Rao observed across thousands of roasts that the best cups came from roasts whose rate of rise declined smoothly, and named the sharp drop at first crack the crash and the rebound after it the flick. The industry adopted both terms within a few years.

The supporting evidence offered is sensory.

He has written that most of his students can taste a roast blind and tell whether its curve crashed, and he presents that as validation of the idea. He also notes that crashed roasts tend to flick and tend to be underdeveloped, so the three often appear together.

That last observation is the weak point, and it is his own.

If crashing, flicking and underdevelopment usually arrive together, then tasters identifying a crashed roast may be identifying the underdevelopment. Separating those requires a controlled comparison, not a classroom.

02 The probe advice undoes the argument

He advises replacing a bean probe thicker than 4 mm before forming strong opinions about how crashy your rate of rise is.

That advice is correct. A thick probe responds slowly, and a slow signal differentiated into a rate curve produces dips and rebounds that the beans never experienced.

Follow the logic one step further.

If the shape of the curve depends on the diameter of a piece of metal, then the curve is describing the instrument as much as the coffee. A feature that appears or vanishes when you change a sensor is not a property of the roast.

Software finishes the job.

Smoothing settings and sampling intervals reshape the same data. A flick can be removed from a roast that finished an hour ago by adjusting a preference. Nothing about the beans changed.

Roasters have reported exactly this.

On machines carrying two sensors, one has shown a crash and flick after first crack while the other, on the same batch, showed nothing of the kind. Same roast, same coffee, two different verdicts.

03 Chemistry settled this before coffee asked

Reaction rate is governed by temperature.

The Arrhenius relationship, named for a Nobel laureate in chemistry and in continuous use for more than 130 years, holds that the rate constant rises exponentially with absolute temperature. How far a reaction has progressed is that rate accumulated over time.

Nothing in it refers to the rate of change of temperature.

A molecule has no access to what the thermometer was doing thirty seconds ago. It responds to how hot it is now and how long it stays there. A crash changes neither of those facts, because the bean is still climbing in temperature throughout.

This is not a gap in the evidence.

A missing study means a question is open. A missing mechanism means there is nothing to study. Coffee is the only field that treats the second derivative of a temperature reading as a flavour input.

04 What the underlying conditions really are

Baked and underdeveloped coffees exist.

They are caused by insufficient heat for the mass in the drum, or by a roast held too long at too low a temperature. Both of those conditions also bend the rate curve, which is why the two keep appearing together.

Confusing the symptom with the cause costs you the fix.

Chase the curve and you adjust the graph. Chase the heat and the mass and you adjust the coffee.

Claim	What supports it	What it overlooks
A crash bakes the coffee	Tasting notes across many roasts	Crashed roasts are usually also short on heat
A flick adds roasty flavour	Observed alongside crashes	Flicks appear and vanish with probe and smoothing
Tasters can identify a crash blind	Classroom demonstrations	They may be identifying underdevelopment
A smooth curve makes better coffee	Long experience	Smooth curves come from steady heat, which is the actual cause

The test that would settle it has never been run.

Match roasts on time, temperature and final colour. Vary only the shape of the rate curve. Have tasters who have not seen the graphs sort them. Publish the result. Until somebody does that, a smooth curve is a preference wearing the clothes of 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: judging green coffee, and which of its numbers are worth reading.