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How-To Guide

Cacao Roast Defects — Scorching, Baking, Tipping and Uneven Roasts

Diagnosing by cause, not by symptom

"It tasted bad" is not a diagnosis. Roast faults have distinct causes, distinct appearances and distinct fixes, and a bean-temperature graph usually tells you which one you are looking at.

Four cover most of what goes wrong.

1. Scorching

What it is: the surface of the bean is damaged by heat that was too aggressive for where the roast was — most often during the drying phase, when the inside is still wet and the outside is not protected.

How it shows: dark or blistered patches on the shell and on the nib beneath; harsh, burnt notes over a bean that is otherwise under-developed. The tell-tale combination is burnt and raw at once.

On the graph: a very steep early climb, or a large gap between applied heat and bean response while the beans are still on the moisture plateau.

Fix: less heat early. Let the drying phase take the time it needs — see moisture and what it does to your roast.

2. Baking

What it is: the opposite failure. The roast took too long at too low an intensity, so the beans were held warm for an extended period rather than actually roasted.

How it shows: flat, dull, papery chocolate. Not burnt, not raw — just uninteresting, with the origin character notably absent. This one frustrates people because nothing looks wrong.

On the graph: a long, sagging curve where the rate of rise flattens toward the end and the beans creep to the finish rather than arriving.

Fix: keep the rate of rise moving through development. Reaching your finish temperature is not enough; how you got there is what develops flavour.

3. Tipping

What it is: the tips or edges of beans burn while the body of the bean roasts normally. The extremities have less mass, so they respond faster to heat.

How it shows: small dark or blackened spots at the ends of beans; a sharp, acrid edge to an otherwise reasonable batch.

On the graph: often invisible — this is a fault of local heat intensity rather than overall curve shape. A drum running close to a fierce flame with insufficient tumbling is the usual cause.

Fix: lower, more diffuse heat, and make sure the beans are actually moving. Which leads to the fourth.

4. Uneven roasting

What it is: beans in the same batch finish at different points, so when you drop them some are under-developed and some are past. The batch has no single roast level.

How it shows: visibly mixed colours in the roasted beans, and muddled chocolate that is hard to describe because it genuinely is several roasts blended.

Three causes, in order of how often they are the culprit:

  • The beans are not tumbling properly. In a drum, this is very often vane length. Cacao is a physically larger bean than coffee, and on vanes cut for coffee it needs more clearance to toss than full-length vanes leave it. Product that cannot toss freely does not roast evenly. We cut the vanes shorter for cacao — see choosing a cacao roaster.
  • The charge is wrong for the drum. Too thin and the beans have nothing to cushion against; too full and they cannot move. Turndown range matters here — see batch sizes.
  • Mixed bean sizes. Large and small beans in the same charge finish at different times, and no amount of technique fixes it. Sorting is the only answer.

The fault you cannot diagnose

Every diagnosis above depends on having a bean-temperature curve to look at. Without one you have the finished chocolate and a guess — you can tell that something went wrong, but not whether you scorched it early, baked it late, or simply never had the beans moving.

That is the practical case for measurement: not that it makes the first roast better, but that it makes every roast after a bad one better. The RoastPilot controller logs and graphs every session, so a batch that disappoints leaves evidence.

Common questions

Why is my roasted cacao burnt on the outside but raw inside?

That is scorching — too much heat applied early, while the beans were still on the moisture plateau and the interior was wet. The surface has no protection at that stage, so it damages while the centre is still drying. Apply less heat during the drying phase and let it take the time it needs.

Why does my chocolate taste flat and dull?

Most likely a baked roast: too long at too low an intensity, so the beans were held warm rather than roasted. Nothing looks wrong, which is what makes it frustrating. The fix is to keep the rate of rise moving through the development phase — reaching your finish temperature is not enough, how you got there is what develops flavour.

Why are my cacao beans roasting unevenly?

Usually the beans are not tumbling properly. In a drum the most common cause is vane length — a larger bean needs more clearance to toss, and full-length vanes do not leave it enough room. The other causes are a charge that is too thin or too full for the drum, and mixed bean sizes, which finish at different times regardless of technique.

What is tipping in cacao roasting?

Small burnt spots at the tips and edges of beans, where there is less mass so heat has more effect. It shows as an acrid edge on an otherwise reasonable batch and usually indicates heat that is too intense and too local — a fierce flame close to the drum, combined with insufficient tumbling.

Keep reading

Where the roast ends and chocolate begins

Everything above is roasting — heat, time, temperature, moisture, how a bean behaves in a turning drum. That is our trade, and we will talk about it all day.

What happens after the roast is a different craft, and not ours. For fermentation, origin selection, winnowing technique, refining, conching, tempering and recipes, go to Chocolate Alchemy — John Nanci has been the reference on craft chocolate since 2004. Their complete bean-to-bar guide, the Ask the Alchemist archive and the forum will take you further than we could, and they run an all-day drum roasting seminar worth the trip.

Get the roast right with us. Get the chocolate right with them.

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