Roasting Contemporary Coffee on a Vintage Machine

Roasting Contemporary Coffee on a Vintage Machine

We roast our coffee on a piece of history, a prototype Diedrich IR-12, a 12 kilo drum coffee roaster that is older than anyone affiliated with this company. This thing is old, speculated to have been built in a garage by Diedrich in the early 80s. It is so old that it doesn’t even have a serial number, a user manual, or any sort of supplementary model-specific information that would be provided with a contemporary production model coffee roaster.

Its history is also largely unknown. It was bought locally, from a friend who had a small roasting  business of his own, and that is the most we know. When we received it, there was no hiding its age. From broken or missing bolts, to scorching from suspected chaff fires, time wasn’t particularly kind to this machine.

When we’ve had mechanical issues in the past, the Diedrich support line has been baffled that this machine is still in use. The main support staff, who are used to advising on Diedrich’s modern roasters, are typically of little help when it comes to our quirky piece of history. We ultimately get put in contact with the owner, who built the machine by hand, to get advice for parts or troubleshooting. 

And as a result, we know this roaster both inside and out. We’ve had to perform all service and repairs ourselves, occasionally recruiting the help of a vintage BMW mechanic who is local to us when we need a second set of hands. It is a relatively simple machine that is perfectly utilitarian. 

Most of the components, like the motors, pulleys, and sprockets, are just general industrial supply parts. So theoretically, this machine should be capable of running forever. There are no computer control systems that require software updates or proprietary parts that could eventually stop being produced. This IR-12 should theoretically be safe from becoming obsolete. 

coffee roaster

In the most basic form, a coffee roaster consists of only a handful of parts. The main component is a rotating drum, inside of which the raw, green coffee is exposed to heat where it undergoes a series reactions, before turning into brown, roasted coffee, capable of producing soluble material when ground and steeped in water.

The drum is turned by a motor. The motor spins a sprocket that is connected to a chain that travels the length of the roaster up the back. As the large sprocket spins, it moves a smaller sprocket that is connected to a spindle that, in turn, rotates the drum. There are just two drum speeds on this roaster, on or off.

Another electric motor powers a fan that acts as a turbine that pulls air through both the drum and the cooling tray. The direction of the airflow is controlled by the roaster (the person operating the machine) who moves a handle that changes the position of a paddle within the duct work.

In one position, a majority of air will be pulled through the drum, in the opposite position, a majority of air will pass through the cooling tray. The manipulation of airflow is critical during certain stages of the roasting process to ensure dispersion of heat, venting of exhaust gasses, and removal of chaff.

The drum is heated via gas burners. The intensity of the heat of the burners is controlled by the manipulation of a dial that measures gas in bars. As coffee beans undergo the roasting process, they require less and less heat as they continue on towards the degree of desired roastedness. 

Once the coffee reaches its desired end point temperature, a calculated moment based on the internal temperature of the coffee, post first-crack development time, a visual analysis of the color and smell test to check for optimal sweetness, the roasting is halted. A large door on the face of the drum is opened and the beans cascade down into the cooling tray. 

coffee beans in cooling tray

The cooling tray is a circle that sits beneath the drum. It is maybe two and a half feet in diameter and maybe 8 inches deep. The bottom of the cooling tray is a grate, where cool air is pulled in from the atmosphere by the same fan that pulls air through the drum near the end of the roasting process. 

The cool air passing over the beans ensures that the roasted coffee beans are brought down to room temperature as quickly as possible. To aid in this, an agitator arm spins within the tray, moving the beans in a circular motion. If a coffee is not cooled quickly, it will continue to roast under its own heat, which would make the attention paid to determine the optimal end point of a roast purposeless. 

When the coffee is fully cooled, a door is opened on the bottom of the cooling tray, and with the help of the agitator arm, the coffee evacuated from the tray into dedicated buckets where it will live until it is packaged the same day it is roasted.

It is impossible to deny that coffee roasters have become far more advanced since our IR-12 was conceived. But the analog, tactile controls force us to take extra care in every step of the roasting process. Having torn this roaster apart to replace a burnt out motor or seized fan, has aided in our understanding of how the machine works. How, despite its seemingly rudimentary design, we are able to manipulate and control the roasting process as effectively as a newer, more technologically advanced roaster. 

Using a machine of this vintage, with its scorching marks and patina and all of its shakes and rattles, keeps us grounded in the fundamental artisan nature of coffee roasting. It keeps us sharp and focused. We are forced to be truly engaged and to respond to the needs of each coffee as we determine when to modify the application of heat or airflow to yield the desired end result: a balanced cup of coffee.

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