Key Observations
Roaster: Gene Café CBR-301
Environment: Indoor roasting (office) under standard kitchen extractor hood
Ventilation: Passive hood extraction with aluminium duct directing exhaust airflow
Smoke behaviour
- Little to no visible smoke during drying and early Maillard stages
- Visible smoke typically begins ~10 minutes into the roast, depending on development level
- Smoke primarily exits via exhaust outlet and vents around the chaff collector
Ventilation effectiveness
- A standard kitchen extractor hood manages visible smoke reasonably well
- Small plumes may appear briefly but are quickly pulled into the hood airflow
Smell vs smoke
- Smoke can be ventilated effectively
- Roasting aroma will still linger, often detectable in the room after roasting
Ducting observations
- 75mm aluminium-lined automotive ducting tolerated heat well
- 100mm aluminium extractor ducting also performed well
- These observations reflect personal experimentation, not recommended modifications
Airflow design
- The Gene Café airflow system is not fully airtight
- Some air (and smoke) can escape around chaff collector vents, which appears normal
Additional note
- Replacement exhaust connector and chaff collector parts are being supplied by Gene Café and will allow further observation of airflow behaviour.
Coffee | One Roast at a Time
One of the questions that comes up repeatedly when people consider roasting coffee at home is simple:
How much smoke does roasting actually produce?
It’s surprisingly difficult to find a clear answer.
Most roasting videos show the roast itself — the colour change, the drum spinning, maybe the first crack — but very few show what happens to smoke and ventilation in a normal domestic environment.
So in this video I decided to document something very simple:
What roasting coffee actually looks like in a real indoor setup.
Not a lab.
Not a garage workshop.
Just a normal room.
In my case, an office.
The Setup
The roaster used here is the Gene Café CBR-301, operating as part of my ongoing home roasting project.
The machine sits under a standard kitchen extractor hood, similar to what you would find in a normal domestic kitchen.
The extractor hood is not physically connected to the roaster.
Instead, I have attached a small aluminium duct to the exhaust outlet which simply helps direct the airflow toward the hood.
There is nothing particularly specialised about this setup.
The aim is not to engineer a perfect ventilation system, but simply to observe what happens during a normal roast.
When Smoke Actually Appears
One of the interesting observations from repeated roasts is that visible smoke does not appear immediately.
During the early stages of roasting:
Drying phase
Early Maillard reactions
there is typically very little visible smoke.
You can smell the roasting coffee of course — the aroma of warm grain, bread, and developing sugars — but visually the machine is usually quite clean.
Where things start to change is later in the roast.
In my experience this typically occurs around the 10-minute mark, depending on the coffee and the level of development being targeted.
At that point you will begin to see small wafts of smoke appearing around the machine.
Where Smoke Escapes on the Gene Café
In my setup the smoke usually becomes visible from two locations:
1. The exhaust outlet
This is the main airflow path where hot air and roasting gases exit the machine.
2. Vents around the chaff collector
Even though the chaff box appears visually sealed, it is not designed to be completely airtight.
The Gene Café relies on airflow moving through the system, which means some air — and therefore smoke — can escape around those areas.
This is not a fault or failure of the machine.
It is simply a consequence of how airflow systems work during roasting.
Smoke vs Smell
An important distinction when roasting indoors is the difference between smoke and smell.
Smoke is actually relatively easy to manage with ventilation.
In this setup, once smoke becomes visible the extractor hood tends to pull it away fairly quickly.
You may see a small plume appear briefly before it disappears upward into the airflow.
The smell of roasting coffee is different.
Roasting produces a strong and distinctive aroma which tends to linger in the room after roasting has finished.
Even with ventilation running, it is quite normal for a faint roasting smell to remain in the room for some time.
In my case it is usually still detectable the following day.
Personally I quite enjoy it.
Others in the household are slightly less enthusiastic.
Exhaust Components and Airflow
During normal use I accidentally damaged the exhaust connector pipe on the machine, and also noticed that the chaff collector gasket was not sealing as tightly as expected.
To stabilise things temporarily I applied a small amount of heat-tolerant sealant around the gasket area.
This is only a temporary measure while waiting for replacement parts.
Gene Café have been extremely helpful and have arranged to send replacement components for both:
- the exhaust connector
- the chaff collector body
Once these arrive it will be interesting to see whether the airflow behaviour changes.
My suspicion is that the overall ventilation pattern will remain fairly similar, but it will be useful to confirm.
Ventilation Ducting and Heat
One practical observation relates to the ducting used to direct the exhaust airflow.
The Gene Café reaches quite high temperatures internally during roasting, so anything attached to the exhaust needs to tolerate heat.
In my own setup I experimented with two types of ducting:
• 75mm flexible automotive ventilation ducting
(the aluminium-lined type often used in vehicle heating systems)
• 100mm corrugated aluminium extractor ducting
(the type commonly used with kitchen extractor fans)
Both of these appear to tolerate the conditions produced by the roaster without any issues during normal roasting.
To be clear, this is not a recommendation or modification guide.
It is simply an observation from my own experimentation while setting up ventilation.
Anyone building their own roasting setup should ensure that all materials used are heat-tolerant and safe for their environment.
Practical Reality of Indoor Roasting
Based on what I have observed so far, the Gene Café is actually quite manageable to use indoors, provided there is some form of ventilation.
A simple extractor hood like the one shown here can handle most of the visible smoke during roasting.
However, roasting in a completely sealed room with no airflow would probably not be ideal.
As with most things in coffee roasting, the practical answer is somewhere in the middle.
Reasonable airflow.
A bit of planning.
And realistic expectations.
A Note on Development and Smoke
Another consistent observation is that the moment visible smoke begins to appear often coincides with later stages of development.
Around this point:
Bean colour moves toward peanut brown
The aroma shifts toward hot bread and toasted nuts
Shortly after that transition, visible smoke usually begins to appear.
Watching the airflow around the roaster during this stage gives a realistic picture of what roasting actually looks like in practice.
Why Document This?
The goal of this project has never been to show perfect roasting environments.
Instead the aim is simply to document what actually happens when someone learns to roast coffee at home.
Real equipment.
Real rooms.
Real observations.
No idealised setups.
Just learning.
One roast at a time.
A Question for Other Gene Café Users
If you are roasting on the Gene Café CBR-301, I would genuinely be interested to hear how you handle ventilation in your own setup.
Do you use:
• an extractor hood
• window venting
• external ducting
• garage roasting
Everyone seems to solve this problem slightly differently.
And comparing real experiences is often the most useful way to learn.