Dirty exhaust systems are the most common cause of roaster fires. Protect your machine, your business, and yourself by installing the proper ducting and ventilation.
Here’s a scenario no coffee roasting professional wants to think about…
You work hard to pursue your passion and start your own roasting company. Money is tight, so you’ve been frugal where you can, and you’ve managed to bootstrap a sustainable business.
Unfortunately, the hidden costs of ducting and ventilation on your machine snuck up on you. You simply installed what you could afford as a result. Maybe it was a standard heat exhaust system like what you would use for a fireplace, something you rigged from the hardware store, or a lower-grade commercial system.
The thing is, coffee roasting operates with a different kind of pressure—something you might not have known. That means that the ventilation you installed wasn’t enough to keep everything clean and safe. Your machine catches fire, part of the building may have been damaged, and you’re lucky that no one on your team got hurt.
This story might seem far-fetched at first, but Diedrich alone receives two or three reports of roaster fires per year on average. After inspection, we find that a dirty exhaust system is the leading cause.
How dirty is the roasting process?
The entire roasting process is dirtier than you think. Every roast discharges oil, chaff, and dust that forms a residue. As that residue cools, it condenses on the internal walls of airflow passages, blowers, chaff collection systems, and the roaster exhaust duct.
We know that the heat environment inside of a roasting chamber is created by a balance of convective, conductive, and radiant heat. A dirty machine changes that heat balance by diminishing the air responsible for it.
The accumulation of residue inside the machine reduces airflow, which means that, all else being equal, you’ll begin to fall behind on your roasting profile. To stay on profile, you might turn up the gas (which is conductive heat) to make up for the lack of convective heat.
This adjustment dramatically changes the roasting medium, which changes the heat transfer rate, which changes how the chemistry evolves, which finally alters the flavor profile of the coffee. When one of the primary goals of any roaster is consistency, that can have disastrous results for your business.
What are the dangers of a dirty roaster?
There’s more at stake than just your flavor profiles. Residue buildup is highly flammable, putting both your equipment and your staff at risk.
With over 6,500 roasting machines installed worldwide, Diedrich receives about two to three fire reports annually. Even when the main parts of the roaster are kept impeccably clean, a dirty exhaust system can still cause a chaff or duct fire.
Methane gas, a byproduct of heating the coffee during roasting, isn’t efficiently removed from the heat environment when there’s too much residue. The vent pipes are supposed to dissipate heat into the outside air. However, as residue builds up internally, it actually acts as an insulator.
The result is increasing, uncontrolled temperatures. As more chaff blows out of the roasting drum with the pressure created by carbon dioxide, it becomes fuel for a fire. The more “fuel” (oil & chaff) there is when a fire does happen, the hotter and longer the fire will burn and the more damage it will end up causing.
How can I protect myself and my business?
The single most important thing you can do as a roaster is to keep every part of your system clean. Most manufacturers provide general guidelines for cleaning their machines, but they are difficult to specify exactly as the proper procedures can vary depending on the particular installation, geographical climate, roasting styles, and other factors.
For example, a moist and humid climate will require more frequent cleaning, especially if it’s cold (which results in more condensation). Similarly, a machine that handles a lot of dark roasts should be cleaned more often as the exhaust smoke carries more oils than in lighter roasts.
Many roasters neglect their ventilation systems, even though this is the most important part.
Ventilation comes in many forms: open air, direct venting, a powered hood, or other custom options. When considering the best ventilation option for you, it’s important to remember that coffee roasting is a positive pressure system rather than a negative pressure system.
That means that, instead of heated air rising so that pressure in the pipe is less than pressure in the room, roasting waste causes pressure in the pipe to be greater than that in the normal atmosphere.
Anything like stovepipes, fireplace venting, or hardware store solutions will not work unless each individual joint is sealed. Even then, it makes cleaning exponentially more difficult and thus less frequent, and it offers no real protection against a potential fire’s high temperatures.
Diedrich recommends installing UL certified, Class-A, double-walled, positive-pressure ducting. In most states in the U.S., it must be installed by a professional company such as VentConnection.com
While these systems might seem expensive up-front, the fact that they keep your machine clean, your staff and customers safe, and your company running smoothly completely justifies the price. Whether you’re looking for a new machine or hoping to update an existing one, this isn’t something to consider. Protecting yourself is something you need to do.
Keeping you and your team safe during the roasting process should be your first priority. Luckily, it’s ours, too. 
