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How-To Guide

Grain Roasting Defects — Scorched, Baked, Uneven and How to Fix Each

Start by cutting the grain open

Almost every grain roasting fault can be identified in two minutes with a handful of the finished batch and something to cut with. Take twenty kernels, not five, and take them from the middle of the batch rather than the top. Split them and look at the cross sections side by side.

What you are reading is the relationship between the outside and the inside of each kernel, and the spread of colour across the twenty. Those two things separate nearly all of the failures below from each other, and they tell you more than the colour of the pile does. A batch can look right in the bowl and be wrong in the kernel.

Scorched and tipped kernels

What you see. Dark or blackened patches on the surface, often concentrated at the pointed ends of the kernels — that is where the name tipping comes from. Cut one open and the interior is markedly lighter than the shell, sometimes still pale. The smell has a burnt edge sitting on top of an otherwise underdone roast, and the flavour is harsh without being deep.

What causes it. Too much heat too early. The outside of a kernel dries and starts colouring while the inside is still wet and pinned near the boiling point of water by the moisture in it. You are burning a surface that is attached to a raw interior. Small and thin kernels go first, which is why the ends tip before the bodies do. Hot metal contact does the same thing locally, so a lightly loaded drum with a hard flame underneath produces it faster than a full one.

The fix. Back the heat off through the drying phase and let the grain set the pace, then bring it up once the moisture has gone. Moisture in grain roasting explains why that phase cannot be rushed. Check your load: a batch far below the drum capacity heats aggressively and unevenly. And make sure the grain is actually tumbling rather than sliding, because kernels that stay against the wall take the damage.

Baked and flat

What you see. The colour is where you wanted it, more or less, and the flavour is not there. It reads dull, papery, faintly like cardboard, without the bread crust or nutty character the colour promised. Cross sections are even, which is the confusing part — nothing looks wrong.

What causes it. Too long at too low a temperature. Colour and aroma are made by the same reactions, but they are not made at the same rate at every temperature. Crawl through the development stretch slowly enough and the colour catches up while the volatile compounds that carry the flavour either never form properly or form and are driven off over the extra time. You end up with the appearance of a roast and the taste of a very long toast.

The fix. Get through the development stretch with some pace. If a roast that is supposed to sit near 350°F for about half an hour is taking you fifty minutes because the grill is struggling or the lid keeps coming open, that is the fault. Preheat properly, keep the lid shut, and stop lowering the heat every time the temperature climbs. A roast that is stalling is heading for baked, and no amount of extra time recovers it.

Uneven colour through the batch

What you see. Your twenty kernels are three or four different colours. Some are pale, some are where you aimed, some are a shade or two past. The flavour is muddled rather than faulty, because it is the average of several different roasts rather than one.

What causes it. Two things, and it is worth working out which.

The first is agitation. If the grain is not being lifted and turned constantly, some of it sits against hot metal and some of it sits in the middle of the mass, and those are different roasts. On a sheet pan this is inevitable, which is the built-in ceiling of the oven method. In a drum it means the load is wrong, the drum is turning too slowly, or the vanes are not getting under the product to toss it. An overloaded drum is a common culprit: past a certain fill the grain stops tumbling and starts sliding as a mass.

The second is size distribution. If your grain contains a wide spread of kernel sizes, or a proportion of broken kernels, the small pieces roast faster than the whole ones and no amount of tumbling makes them the same. That looks like a roasting problem and is actually a sorting problem.

The fix. Load the drum to the range it was built for rather than filling it, check that the product is genuinely tumbling and not sliding, and screen out fines and broken kernels before they go in if the sack is rough. Where the batch is a mixture of genuinely different sizes, expect a spread and roast to the average rather than the extremes.

Acrid, ashy, burnt

What you see. Uniformly very dark, often with a dusty surface. The aroma is sharp and ashy rather than deep and roasty, and it catches the back of your throat. Where a good dark roast smells like a roastery, this smells like a bonfire.

What causes it. Overrunning the dark end. Colour development accelerates as temperature rises, so the last stretch of a dark barley or chocolate malt roast moves several times faster than the beginning did, and the window between deep and destroyed is well under a minute. People who have only roasted amber are used to having time to decide, and the dark end does not give it to them. Loose chaff and dust smouldering in the drum add their own ashy note on top.

The fix. Watch product temperature rather than the clock in the final stretch, and know your stopping number before you start rather than deciding in the moment. Pull earlier than feels right and let residual heat carry the last of it. If you are approaching the dark end without a probe in the grain, you are guessing at the fastest-moving part of the roast.

Grain lost through the drum

What you see. The batch that comes out weighs noticeably less than the shortfall moisture alone could explain, there are kernels on the burner and in the bottom of the grill, and the roast picked up a scorched smell that does not match the colour of the grain you recovered.

What causes it. The perforation is bigger than the product. A standard drum is perforated 3/16" because that suits coffee, and small grain simply falls through it. The fines and thin kernels go first, then anything that cracks during the roast, and everything that lands on the flame burns and sends smoke back up through the batch you still have.

The fix. The correct mesh for what you roast, chosen at order time. Mesh and hole size walks through it properly, but the short version is that small grains such as quinoa and barley want the 1/16" drum, large grains and coffee and nuts are fine on 3/16", and powders need a solid drum. Choose for the smallest particle in the batch rather than the average one.

Two more worth knowing

Pale and grassy after a long roast. The grain never got out of the drying phase, usually because the load was too big for the heat available or the lid spent too much time open. It is not underroasted in the sense of needing another five minutes; it is a roast that never started.

Grain that will not store. Sealed while still warm, so the last of the moisture condensed inside the container and went back into the batch. Cool to room temperature on a wide tray before anything goes into a jar.

Working through it

In order: check whether the fault is on the surface or through the kernel, check whether the batch is one colour or several, then check load, agitation and mesh before you touch the heat. Most people adjust temperature first, and most of the time temperature is not the problem.

Consistent equipment removes most of this list permanently — continuous tumbling deals with unevenness, the right perforation deals with lost grain, and a probe in the product deals with overrunning the dark end. See the drum roasters we build for grain.

Common questions

Why are the tips of my kernels burnt but the middles still pale?

That is tipping, and it comes from applying more heat than wet grain can absorb. The kernel surface dries and begins colouring while the interior is still held near boiling point by its own moisture. Ease off through the drying phase, make sure the drum is loaded near its intended range, and let the temperature rise once the water has gone.

What does baked grain taste like and can it be saved?

Dull and papery, with the colour of a proper roast but none of the aroma behind it. It is caused by spending too long at too low a temperature, so the volatile compounds that carry flavour never build or are driven off. It cannot be recovered afterwards; the fix is to get through the development stretch with more pace next time.

How do I stop a dark roast turning acrid?

Decide your stopping temperature before the roast rather than during it, and watch the grain rather than the clock in the last stretch. Colour development speeds up as temperature climbs, so the final minute of a dark roast moves faster than the first ten. Pull slightly early and let residual heat finish the job.

Is patchy colour a heat problem or an equipment problem?

Usually equipment or loading rather than heat. Grain that is not tumbling continuously roasts as a stack, with the kernels against the metal running ahead of the ones in the middle. Check that the drum is turning the product rather than sliding it, that the load sits in the range the drum was built for, and that a wide spread of kernel sizes is not doing the work for you.

Keep reading

Where the roast ends

We build roasters. What you do with the grain afterwards — mashing, brewing, distilling, baking, blending a grain bill — is its own craft and a deep one, and it is not ours. Unlike coffee, there is no single authority we can hand you to: brewing knowledge lives in forums and clubs rather than with one gatekeeper.

That gap is why we wrote these pages. Ask us about drums, mesh sizes, grills, burners, motors, thermocouples, batch sizes, or why half your barley came out two shades darker than the rest, and you have our full attention.

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