Air roasted vs drum roasted: what changes in the cup

The short version: a drum roaster cooks coffee against hot metal, and an air roaster cooks it in a vortex of hot air. In the cup, air roasted coffee usually tastes cleaner and less bitter, and drum roasted coffee tends to taste heavier and more toasty. Most of that comes down to two things: how the heat gets into the bean, and what happens to the chaff.

We roast every bean at Kribi on air roasters, so we're not neutral here. But drum roasting isn't the villain of this story, and it helps to know what each one actually does before you pick a side.

Two ways to heat a bean

A drum roaster is a rotating steel barrel sitting over a burner, usually gas. The beans tumble inside it and pick up heat two ways: from touching the hot drum, and from hot air moving through the barrel. The contact part is the one that matters here. A bean pressed against hot metal heats from the outside in, and faster on whichever side is touching.

An air roaster skips the hot surface entirely. Air blows up through the bottom of the chamber fast enough to lift the beans off the floor and keep them moving, so each bean is heated by the air around it, on every side at once. People in the trade call it fluid bed roasting.

Ours have a clear chamber and run on electricity. You can stand at the counter and watch a batch go from pale green to tan to brown while the beans bounce around like popcorn.

A batch takes about 10 to 15 minutes, so speed isn't really the difference between the two. If you order a roast at the counter, plan on about 20 minutes from green beans to a bag in your hand. Or grab a bag off the shelf that we roasted that week. That one's ready to go.

What changes in the cup

Bitterness

This is the difference most people notice first. Every coffee bean sheds a thin, papery skin called chaff as it roasts. In an air roaster, the same airflow that's roasting the beans lifts the chaff away the moment it comes loose and blows it into a collector.

Drum roasters pull chaff out with an exhaust fan too, but not as fast, and some of it hangs around in the barrel next to the beans. Chaff that sits in that heat scorches, and the smoke settles right back onto the coffee. A lot of the ashy edge people think of as coffee's natural bitterness starts there.

Body

Here's where drums have a real case. Drum roasted coffee often has a heavier, rounder body and that familiar toasty flavor a lot of us grew up on. If that's the cup you love, nothing is wrong with your taste. Air roasted coffee tends to feel lighter and cleaner on the tongue, which some people read as "less coffee" until they've had a few cups of it.

Where the coffee grew

Take away the scorch and more of the bean itself comes through. Our Mount Oku is grown at about 1,370 meters on the volcanic slopes of Mount Oku in Cameroon's Northwest region, washed, and roasted light. In the cup it's caramel and red cherry with a little floral lift at the end. Those are exactly the notes that disappear first under smoke.

Dark roasts

Air roasting doesn't turn every coffee into a light roast. A dark roast like our Hyperslap espresso still tastes dark. It just doesn't taste burnt.

Even heat, start to finish

In a drum, the beans touching the wall run hotter than the ones in the middle of the pile, and the outside of each bean can get ahead of the inside. Good drum roasters manage that with skill, and plenty of great coffee comes out of drums because of it.

In an air roaster, most of that problem isn't there to begin with. Every bean floats in the same hot air and gets the same heat on every side, so a batch comes out the same color all the way through. That evenness is a big part of why the flavor stays clean from one batch to the next.

How to tell which one you're drinking

If the bag doesn't say, assume drum. It's how the vast majority of the world's coffee gets roasted, from grocery store cans to most specialty roasters. Air roasters are rare enough that the people who use them usually say so up front.

Your tongue can help too. Drink it black and pay attention to the finish, the taste that's left a few seconds after you swallow. A dry, ashy finish that hangs around usually means smoke got in somewhere along the way. A finish that fades clean, or leaves a little of the fruit behind, is what we're chasing with every batch.

Why we went with air

Our take, after years of roasting this way: a lot of people who reach for cream and sugar aren't covering up coffee, they're covering up smoke. Pour them a cup without it and plenty of them stop reaching.

Taste it side by side

At both of our cafes, in Oak Park and Forest Park, Illinois, the roaster sits right in the shop. We roast in small batches there and will roast any coffee on the shelf to order for you. Bags ordered on the website are roasted at our roastery in Chicago and shipped from there.

The easiest test happens in your own kitchen. Brew a bag of Mount Oku the way you always make coffee, pour whatever you usually drink next to it, and taste both black before anything goes in either cup. Then taste them again once they've cooled a few minutes, because that's when smoke and scorch stop hiding.

Want to know more about how the roasters work? Start with what air roasting is, and why we roast this way, or read our air roasting page.