How Does Airflow Affect the Roast

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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#1: Post by Dregs »

I have wondered whether the relative amount of airflow during the roast would change the taste in the cup. In other words, does higher airflow and heat input produce a roast that tastes better/worse/different from one with less airflow and heat input in a particular roaster? I never quite got around to trying a systematic experiment.

Sometimes, good things come to those who procrastinate. Boldjava and crew are going to answer the question plus talk about cupping on Wednesday:

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#2: Post by [creative nickname] »

I'm very much looking forward to the video. It may also be of interest to know that I plan to make airflow a particular focus of the discussion during the November-December R&L thread that I'll be hosting.
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#3: Post by HoldTheOnions »

If you search, there is a study out there in relation to commercial roasting where their conclusion was that high air flow is bad. Not sure how it translates to home roasting though.

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#4: Post by fu11c17y »

A fun analogy I like to visualize is like riding a bike, what gear do you decide to use. It's not an exact analogy but it's about using the right level of fan for the intended heat applied to the BM... at what stage of the roast. Are you going uphill, or downhill, or coasting? Too much fan is bad, too little fan is bad.

- Coffee Factorial. San Diego, CA

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#5: Post by Boldjava »

Since attending Joe's roasting course at Cafe Imports (, I have been playing with a bit more airflow.

Roasting on the North TJ-067 (natural gas). Plenty of umpf available with this fan arrangement. I have eased a bit more air into the stages with some success and some failure. I got one very nice roast. But when I tried to introduce more air into successive roasts, I lost convection heat in the midst of first crack. It will take more time, patience, and experience.

Joe suggests that a bit more air than I had been using will help with the sweetness of the coffee. I believe the fan's capacity might well be greater on this roaster than others (minimal experience on Diedrich, Probat, and USRC). Looking forward to Joe's/Tony's discussion and Mark's Nov Roast and Learn. Lots to learn!

Previously used these settings on the TJ-067 under a 1K charge:
90 sec: min air, 18% setting, just enough to keep fan spinning
90-1st crack: 35% setting
1st crack to end of roast: 40% setting

Successful improved roast:
90 sec: min air 18%
90 sec-1st crack 45%
1st crack - end of roast 60%

Still experimenting. Not finished playing.
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#6: Post by SJM »

It's hard for me to imagine that this question can be dealt with generically.
I would expect it to be roaster specific, and if not that at least solid/perforated drum specific.

But, Joe has been so instructive on enough subjects that I will be interested to hear what he has to say :-)))
Thank you Mill City Roasters for bringing us these tutorials.

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#7: Post by ciel-007 »

On a recent trip to San Francisco, I spent quite a bit of time chatting with one of the roasters at Four Barrel Coffee on Valencia.

The profiles he followed with the old Probat were similar to the ones I use with my BellaTaiwan XJ-101... with one exception: the cyclone fan is kept at maximum at all times.

He claimed that the high air flow prevents the smoke (and other emanations produced during the roasting process) from contaminating the delicate flavors of the resulting roast.


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#8: Post by JK »

I just read some good info here:

Generally, if you are getting moisture loss readings over 18%, you are either producing darker roasts beyond the Full City level, or you may have too much airflow which is excessively stripping the moisture from the coffee (this could also come from excessive heat input towards the end of the roast, which could also be affected by airflow depending on the roaster type). No matter what the actual reading is, it can also tell you how consistently you are achieving your desired profile from batch to batch. Consistency from batch to batch is at the end of the day the goal of creating a roast profile.
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#9: Post by Dregs (original poster) »

I watched and really enjoyed the video at Mill City. Excellent information as always and even good video quality! While the conversation didn't specifically address the question in my first post about how airflow affects taste in the cup (my misunderstanding of the topic), it had a boat-load of good tips for managing airflow. I'll comment on just one right now that I enjoyed immensely.

Joe talks about the "divot" in the bean temperature ROR curve after the start of 1C (about 30:40 in the video). He differentiates between the divot and the flick of death. The divot is a dip in the ROR curve caused by the release of steam from the slightly cooler interior of the beans. The ROR curve would follow a smooth decline except for the divot. If the curve rises at the end of 1C, that's the flick of death. Divot is OK; flick is bad. Thanks, Joe, I don't don't need to worry about the darn divot anymore!

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#10: Post by OldmatefromOZ replying to Dregs »

Yeah another great video, really great format, thoroughly enjoyable the open style of interaction / sharing with people who do it for a living.

Thank you