Charcoal Grill Coffee Roaster

It’s not exactly common to come across green coffee beans at the grocery store, but there’s a whole store in Oakland that sells them. As soon as I learned it was possible I had to try.

There are two components, the roaster and the spacer. I ended up making two versions of the roaster itself, but the spacer has worked just fine.

Like pretty much all of my projects, I made this roaster at Techshop. It's also included in my challenge to myself to Make 100 Things.

I purchased steel hardware cloth from Cole’s Hardware and several pipe clamps to hold the cylinder’s shape. A simple threaded steel rod and some pipe caps finished off the roaster. I fitted the metal pieces at Techshop, mostly because I love working there but also because they have nice tin snips that made the work much easier. This could easily be done at home.

After the first roast, we found that 1/4” squares in the hardware cloth were too big for many beans (half of the Ethiopian beans spilled out as we were just about ready to put them on the grill) so we improvised for the day by lining the cylinder with aluminum foil. This worked well but left me looking for a piece with smaller openings to improve the roaster.

The spacer was a less obvious piece but necessary in my situation as the grill we are using is brand new and the steel rod would damage the sides. Depending on your grill, this piece could be optional. I took dimensions of the grill and whipped out a plywood spacer on the CNC mill at Techshop that has a channel for the rod and sits nicely in the bottom of the grill. If you're making your own, I suggest the following:

- Cut out a ring with space inside and outside the rim of your grill's bottom layer
- Provide a groove for the bottom of the grill to sit in. This will stabilize the spacer and keep it in place while roasting.
- Cut a channel across the center diameter of the ring for the steel rod of the roaster to sit in as it turns
- I put in a groove in the top for the lid to sit on as well, and I'd recommend against that. The lid will sit still on its own and if the lid is thin metal on the end like this one, if the lid sits in the groove it'll actually get in the way of the threaded steel rod spinning.

The wood, not surprisingly, browned due to heat exposure within the first two roasts so I wrapped the wood in foil for protection. The next improvements will be finding the hardware cloth with a smaller grid, possibly attaching a slow-speed motor, and protecting the wood. V1 also left me looking for a sturdier solution for the end caps as the fit was excellent with these pieces but the small beans finagle their way out.

Fun fact: Did you know as coffee beans roast, they lose water and
increase in size? Check out the photo of the green coffee bean and roasted coffee bean from the same batch above.

This second version has served us well for many roasts. Below is a list of improvements to the roaster, though the spacer has stayed the same with the addition of protective foil.

1. New wire cloth.

The first wire cloth had larger openings and some of the beans fell through the openings, so we lined the inside with aluminum foil. Functional solution, but it made checking the color of the beans throughout the roast more difficult and also kept the natural chaff from falling off during the process.

2. New end caps.

Stronger, longer, and much easier to drill into. I fixed one end cap to the steel rod and the other floated so that it was easier to remove and get the beans out quickly.

3. A window crank from my hardware store.

Simple solution (window crank and epoxy) that made the whole process a lot more enjoyable.

4. We put aluminum foil over the plywood cutout on the grill.

This was to protect the wood from the heat and seemed to work really well.

We also learned some things about roasting.

A. It’s darn near impossible to get the heat even in the grill, but after two roasts we got the idea to pick up the whole roaster and shake up the beans a few times throughout the roasting period to make sure all beans are heated more or less evenly. The photo above shows a person holding the roaster before it's hot but make no mistake - you'll want work gloves or at the very least kitchen mitts when you shake the roaster. Before we thought of this, the roast was all over the place - check out the photo above and you’ll see the whole spectrum of roasting from one of our first batches.

B. The grill should be level, or all the beans will end up falling to the low end of the roaster. (Seems quite obvious now.)

C. Roasting in a windy place can be handy. After we emptied the beans into a metal colander, I stirred the beans to cool them down and the excess chaff floated away. So with the help of my two viking gentlemen, we had a productive and relaxing afternoon of roasting. The high temperatures over four roasts left the little roaster that could with a gold tint, but it’s still seems perfectly in tact for future roasts.