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How-To Guide

Roaster Drum Mesh and Hole Size — Solid, 1/16" or 3/16"

Half the barley went through the drum

It is one of the most common ways a first grain roast goes wrong, and it is entirely mechanical. Someone buys a drum roaster, loads it with barley or quinoa, starts the motor, and watches a steady trickle of grain fall out of the perforations and onto the burner. By the time they stop it they have lost a chunk of the batch, filled the grill with smouldering kernels, and learned something about hole size the expensive way.

Nothing was defective. A drum built for coffee is perforated for coffee. Coffee beans are large enough that a 3/16" hole holds them comfortably while letting air, smoke and chaff move through the bed. Put something smaller in the same drum and the same holes stop being ventilation and start being a sieve.

So mesh hole size is not a detail on the spec sheet. For grain it is the first decision, ahead of capacity, ahead of controller, ahead of everything except whether the drum fits your grill.

What ships on every RK drum

Mesh Hole Size is a selectable option on every drum we build, at every capacity from 2 LB through 4, 6, 8 and 12 LB. There are three:

  • Solid — for ultra-fine grains & powders, such as granola & flour
  • 1/16" — for small grains, such as quinoa & barley
  • 3/16" — for large grains, coffee, cacao, corn & nuts

3/16" is the standard, because coffee is what most drums get used for. If your roasting is going to be grain, the standard is very often the wrong answer.

The rule: sort by the smallest particle, not the average

This is the whole decision in one line, and it is the part people get wrong even when they are thinking about hole size at all.

You are not choosing for the grain as it is described on the sack. You are choosing for the smallest thing that will actually be in the drum. A sack of barley is not uniform. It contains broken kernels, a fraction of thin and undersized grain, dust and fines that settled to the bottom during transport, and whatever bits of husk came along. Malted grain that has been handled a few times contains more of all of that. The average kernel might sit happily on a 3/16" perforation while the bottom ten percent of the size distribution pours straight through.

The practical test is easy: take a handful from the bottom of the sack, not the top, and see what fits through the hole. If anything does, that fraction of your batch is going into the fire, and it is the fraction most likely to scorch and smoke on the way there.

The same rule applies to anything you intend to roast that arrives already broken or cracked. Cracked corn is not corn for this purpose. Grist is not malt. Size the mesh for what is in the drum on the day.

What each option is actually for

3/16" — the standard perforation

The right choice for large grains, coffee, cacao, corn and nuts. Whole corn kernels are big and dense and stay put. Coffee, cacao and tree nuts are all larger than the hole by a comfortable margin. The open area gives you the best airflow of the three, which means smoke and chaff clear out of the bed continuously instead of sitting in it, and the drum breathes.

Keep 3/16" if grain is a sideline and coffee, cacao or nuts are your main use, and accept that small grain is off the menu on that drum.

1/16" — small grains

This is the grain mesh, and for most people reading this cluster it is the correct order. Quinoa and barley are the named examples for good reason: both are small enough to escape a 3/16" perforation and both are staples of home grain roasting. Wheat, rye and small malted barley belong here too.

The hole is small enough to hold the grain and its broken fragments, and still open enough that air moves through the bed. You keep most of the ventilation advantage of a perforated drum while losing the sieve behaviour. If you are roasting malt at home, or taking barley to the dark end for barley coffee, this is the one.

Solid — powders and the very fine stuff

For ultra-fine grains and powders, such as granola and flour, no perforation will hold the product. A solid drum is the only option that works, and it changes how the roast behaves in ways worth understanding before you order it.

What a solid drum changes

With no holes there is no airflow through the bed. Heat arrives almost entirely by conduction through the hot steel and by contact between particles, rather than by hot air passing through. Functionally, a solid drum behaves much more like a rotating pan than like a perforated roaster.

Three consequences follow, and none of them are dealbreakers if you know about them:

  • Agitation matters more. The product touching the wall is taking the heat. If it is not being lifted and turned constantly, that layer scorches while the middle of the load stays pale. Drum speed and load level stop being convenience settings and start being the thing keeping the batch even.
  • Smoke and chaff do not clear themselves. In a perforated drum, volatiles and husk leave through the holes as the drum turns. In a solid drum they stay in the load and around it until you open something, so you have to manage clearing them deliberately rather than assuming it happens.
  • You need to watch it more closely. Fine product has enormous surface area relative to its mass. It picks up colour faster than whole kernels and it goes from where you wanted it to somewhere you did not in less time than you expect.

None of that makes a solid drum a compromise. It makes it a different instrument, and for anything powdered it is the only one that will hold the product at all.

Choosing when you roast more than one thing

Here is the honest version. There is no single mesh that is optimal for flour, barley and whole corn at once. If you roast across that whole range, you are picking a compromise or you are picking more than one drum.

Most people are best served by choosing for the smallest thing they roast regularly rather than the thing they roast most often. Going down a size costs you a little airflow. Going up a size costs you product through the holes, and there is no recovering that mid-roast. A 1/16" drum will roast corn and coffee perfectly well. A 3/16" drum will not roast quinoa at all.

If your roasting genuinely splits across two extremes — a coffee habit and a flour habit, say — a second drum on the same rotisserie is usually cheaper and far less annoying than fighting the wrong perforation on every batch.

Vanes, while you are specifying

The vanes are the internal ribs that lift the product and tumble it back through the bed as the drum turns. They are cut shorter for cacao and nuts than for coffee, because those are physically larger and need the clearance to toss properly rather than jam. It is the same principle as mesh: the geometry inside the drum is matched to the size of what you are putting in it, and getting it right is the difference between a batch that turns and a batch that slides.

Getting the order right

Pick the capacity that suits your usual batch size, then pick the mesh for the smallest particle you expect to roast. For most people arriving from grain roasting, that is 1/16". Configure a drum for grain here and choose the hole size on the product page before you add it to the cart, because it is built into the drum rather than swapped later.

Next: the named grain roasting defects, including what lost grain and poor agitation actually look like in the finished batch.

Common questions

Will barley fall through a standard coffee roasting drum?

Much of it will. Standard drums are perforated 3/16 inch to suit coffee, and a good fraction of any barley sack is small or broken enough to pass through a hole that size. The fines and thin kernels go first, followed by anything that cracks during the roast. Order a 1/16 inch drum if barley is on your list.

Which mesh hole size should I order for quinoa?

The 1/16 inch mesh. Quinoa is one of the two grains that option exists for, and it is far too small to sit safely on a 3/16 inch perforation. The smaller hole still lets enough air through the bed to clear smoke, so you lose very little compared with the standard drum.

Can a solid drum roast coffee and whole grain as well?

Yes, though it handles differently. Without perforations there is no air moving through the bed, so heat arrives mainly through the steel and smoke stays with the load until you clear it. Expect to pay closer attention to agitation and to venting than you would with a perforated drum.

Can I change the mesh hole size on a drum I already own?

No. The perforation is part of how the drum is built, so it is chosen at order time rather than swapped afterwards. If you need two very different hole sizes, a second drum on the same rotisserie setup is the practical route.

Why does corn stay on the standard 3/16 inch mesh?

Whole corn kernels are large and dense enough that a 3/16 inch hole holds them with room to spare, and the extra open area gives better airflow through a heavy load. The exception is cracked corn, which behaves like a small grain and needs the 1/16 inch drum.

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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