What You Are Actually Controlling When You Roast

Roasting, In Practice · Part 1

You do not control roast level. You control how much heat goes in, how much air moves through, and how long it lasts. Everything else is a consequence.

01 There are only three inputs

Heat is the first.

Gas pressure, burner output, element power, whatever the machine calls it. This is the energy going into the batch, and it is the only thing that raises bean temperature.

Airflow is the second.

How fast air moves through the drum. It carries heat to the beans, carries chaff and moisture away, and decides how much of the energy you applied actually arrives.

Time is the third.

How long the beans stay in there, and how that time is distributed between the stages. Time is not set directly; it is the result of the other two, and that distinction matters more than it sounds.

Batch size belongs here too.

Loading a 30 kg machine with 12 kg is a different machine from loading it with 28 kg. The relationship between drum mass, bean mass and heat changes completely, and a profile that worked at one charge weight will not transfer to another.

02 What the beans are doing while you do that

First the water leaves.

Green coffee holds around a tenth of its weight in water. Until most of it is gone, the bean cannot get much above the boiling point, and the energy you add is spent on evaporation rather than on temperature.

Then the browning reactions start.

Sugars and amino acids react and produce colour, aroma and the compounds behind sweetness. This is where most of what you will taste is created, and it takes time as well as temperature.

Then the bean starts producing its own heat.

Around first crack the reactions inside turn exothermic and the bean pushes back. The machine is no longer the only heat source, which is why the same burner setting behaves differently before and after that point.

None of these stages wait for you.

They happen in order and they overlap. Your three inputs decide how long each one gets, and that is the whole of roasting.

03 Things people treat as controls but are not

Roast level is an outcome.

Light, medium and dark describe where you stopped. Two roasts can finish at the same colour and taste nothing alike, because the path there was different.

Total time is an outcome.

Chasing a twelve-minute roast by turning the heat up shortens the wrong stage. The number moves and the cup gets worse.

Bean temperature is a reading, not a lever.

The probe tells you where the batch is. It does not tell you what the beans are doing unless you know how much heat and air produced that number.

04 Change one thing at a time

Each input moves the roast in a recognisable direction.

Move two at once and you learn nothing about either.

If you change	What happens in the drum	What tends to show in the cup
More heat early	Drying finishes sooner, browning starts earlier	More body, risk of scorched edges
Less heat late	Development slows, the bean may stall	Flat, papery, grassy notes
More airflow	Faster convection, chaff and smoke cleared	Cleaner, more defined acidity
Less airflow	Smoke stays in the drum	Heavier, sometimes ashy

Write down what you changed and what you tasted.

A roast log with three inputs and one sentence about the cup is worth more than any curve you copy from someone else's machine.

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: rate of rise, what it measures and what it cannot tell you.