DIY coffee roasting [Part two: roaster designs]

Coffee roasting; how complicated could that be? Just heat some beans until they turn brown, and you’re good to go. I recently found some local green coffee suppliers and realized I can buy small quantities for a fairly reasonable price. So I decided I would build my own coffee roasting setup. This is my journal.

While it was appealing to build my own roaster, if a company had a low-priced, good looking unit I figured it might not be worth going through all the effort designing something…

Retail roasters

There are many home roasting options, but in general I thought they were either expensive and not good quality, or extremely expensive and of very good quality. Common recommendations are the FreshRoast series, the Behmor 1600, or a Hottop; I’ve listed them below with a few comments:

Screenshot 2019-04-05 at 10.22.08
The FreshRoast series appears to be a glorified popcorn popper, with a roast size of just a few hundred grams. The price on amazon.ca is much higher than you typically see. A used one should run you about $200 CAD
Screenshot 2019-04-05 at 10.21.24
The Behmor 1600 is a drum roaster and comes with fairly good reviews from amateur roasters. It can typically roast close to a pound at a time, but is difficult to achieve reproducible results (reviews state this, I’m not totally sure why). This seems like a good option, except the price listed above is in USD and is a big initial investment.
Screenshot 2019-04-05 at 10.19.02
The Hottop seems to be the holy grail of home roasting equipment. It allows for extremely reproducible results, has a cooling tray, and offers a lot of control etc. Clearly $1-2 k is out of the question, but if home roasting became a very serious thing, I would consider jumping directly to this and skipping the Behmor-level gear.

Essentially what I found was that no commercially available roaster fit my needs and budget. Apparently there is a significant number of people who feel the same way. So many, that there is a subReddit almost exclusively for us.

DIY roasters

The r/roasting page is full of people who, like me, want to roast beans at home but not spend too much money. The most common solutions are “popcorn air popper” (so smart!) and to a lesser extent, bread machine + heat gun (uh-oh…)

The air popper solution is kind of perfect; the device gets to the proper temperature, and the fan agitates the beans, just like a fluid bed roaster. The major problem that people run into though, is controlling the temperature or batch size. As far as control, most air poppers don’t even have a temperature reading let alone temperature control. People on Reddit seem, for the most part, to be satisfied with letting the popper reach whatever temperature it reaches, and listening for the cracks.

I like the idea of the air popper, but the idea of having such little control over the process sounds terrible. Lucky for me, Mark Sanders already put together directions for adding a thermocouple and temperature control to any existing popcorn popper. Using a Raspberry Pi microcomputer and a few external components, he built a device that, based on the temperature reading from the thermocouple, will turn the heater on or off. He also wrote a program (in Python) that lets you record the temperature as a function of time save your roast profiles, and repeat profiles you liked. Effectively, this will turn your popcorn air popper into a FreshRoast SR500. Sign me up!Screenshot 2019-04-08 at 16.30.09

This got me so excited that I went ahead and ordered all the parts I was going to need including green beans, and picked over Value Village for a popper. From what I read, most popcorn poppers will work, though in some cases a popper may have trouble reaching a high enough temperature. Typically the older poppers will work better. I ended up finding a beautifully age-yellowed popper that was conspicuously clean and oil-free for a measly $5.00

This is going to be so much fun…

DIY coffee roasting [Part one: Louis-Camille Maillard]

Coffee roasting; how complicated could that be? Just heat some beans until they turn brown, and you’re good to go. I recently found some local green coffee suppliers and realized I can buy small quantities for a fairly reasonable price. So I decided I would build my own coffee roasting setup. This is my journal.

I understand coffee roasting on a superficial level. Beans come dried and unroasted (“green”). By heating the beans, they undergo some sort of browning reaction that makes them delicious. Along the way, the beans “crack”, a lot like popcorn would. There are two cracks that happen, and passing through the “second crack” results in an oily dark roast.

With a bit of research I learned the browning process is due to a specific chemical process called the Maillard reaction. Louis-Camille Maillard was a French scientist who first characterized the process while attempting to reproduce biological protein synthesis. In essence, this is a heat-initiated reaction between amino acids and sugars and is ubiquitous throughout cooking. The browning on steak? Maillard. Brown crust on bread? Maillard. And most importantly, roasted coffee; Maillard.

Clearly the resulting compounds of the Maillard reaction are not identical in all of the above examples. During the reaction, a cascade of molecules are created which depend on the specific amino acids present. The resulting molecules are what give these foods their distinct flavors and aromas, however, the exact collection of molecules that are created are very hard to predict and control. For this reason, I am going to assume most coffee roasting discussion will be more of an “art” than a “science”.

[Is “art” what happens when the science is too complicated? The art of coffee roasting, the art of winemaking, cooking as an art; there are countless examples. Is this admitting that heuristic approaches are required because a process is too hard to fully control? By simplifying details, making approximations, and losing exactness, are we admitting science has failed to describe the process? No. What science has allowed us to do is make informed decisions about how and what to simplify to create a working description that matches the tools we have to enact the process.]

From what I have read, coffee gets tasty between 150-230 C (300-450 F). Along the way there are chemical events that happen at specific temperatures. For right now, those details are unimportant. What is important is that the roaster can reach temperatures up to 230 C (450 F), and will provide even heating to all of the beans. Most commercial solutions seem to involve either a rotating drum which agitates the beans as they heat, or blowing hot air such that the air agitates the beans.

I wonder if I can do better…

Further reading and sources:

[1] The first place you should go (Wiki)

[2] Coffee and the Maillard reaction

[3] Coffee roasting and equipment

IMG_20181229_120336-01