Messing with the I-Roast Chaff Collector.

I did a bunch of crazy testing with homemade chaff collectors for the i-Roast. It so happens that if you remove the top screen, a 4″ piece of ducting fits in perfectly. So I bout a couple chimney caps at home depot, lined them with aluminum screen on the inside, to create basically a giant chaff collector. I was excited: it was cheap ($8), fits perfectly in the top, looks nice … but I was having trouble getting the heat adjustments in the roast settings right. I think in HVAC terms that the chaff/stock chaff collector is creating a degree of “backflow pressure” and my oversized homemade chaff collector relieved the backflow too well. I need to spend more time with this, but it has great potential. If anyone else wants to tinker with it, it’s 4″ OD ducting that fits snugly in the top once you remove the fine screen of the chaff collector. I left the interior ring in place in my tests to help keep the heat in the roast chamber.

Okay – dumb experiment Number 1 – if you noticed your i-Roast came with a metal ring that is used to attach 4″ ducting. The idea is to help direct smoke into a stovetop hood or out of a window. But my goal with finding an alternate chaff collecting solution is to allow all coffees to roast the same regardless of the amount of chaff they produce. To do this, I want a chaff collector that is big enough that airlow out of the roaster is unimpeded by large amounts of chaff, or to simply blow chaff out of the roaster wihout any collector (like an air popper). So I did a series of roasts simply directing chaff into the nearest object I could grab … a trash can. I did not ajust the i-Roast roast levels and the result was two-fold – great agitation throughout the roast, but sadly the roast did not fully develop – I was simply letting too much heat escape the roaster.

From this I realize that the i-Roast needs some “backpressure” in the airflow to help heat the roast chamber. So if decafs create are under-roasting, then an empty stock chaff collector must not provide enough backflow in and of itself to heat the roast chamber enough – the i-Roast must actually need some form of chaff collection or chaff buildup. But how to stabilize this variable? I would like to come up with a chaff collector that has both a large chaff collection area and restricts air to create the backflow pressure.

What about a chaff collector that has airflow adjustment. Think about a cheapo barbeque grill with a rotating disc and a series of holes that can be adjusted to a measure of openness … or closed. That would be ideal.

These 3 roast chamber photos show very good agitation and even roast development in the i-Roast with a vent hose attached and no chaff collection. Actually, the i-Roast with stock chaff collector would look nearly the same but I felt it was slightly better with my vent hose/no collection setup. But the roast stalled right before getting into 2nd crack, so this design is not practicable.

Okay – here is my second attempt. I was at the home depot (I seem to always be at the home depot…) and was noticing how the stock vent caps might fit the i-Roast. In fact they do. If you remove the top of the chaff collector (just the fine mesh screen part that seems to be where the air flow really gets blocked with chaff), you can but in a 4″ ducting piece and if fist just perfectly!
I wrapped it with a fine screen mesh – since this is just a test to see how the roaster behaves, I wasn’t going to do much work. Ultimately I would line the inside with a metal or aluminum fine screen to prevent fine chaff particles from flying all over the place.

This model of vent cap is soft aluminum and has lots of downward facing openings. These tent to create a lot of backflow pressure, and I figured I could easily push in some of the opetinigns to close them an “adjust” the air flow.

I had similar results as the open duct tube. I had consistent and good agitation with different types of coffee (that yield different amounts of chaff) but could not get a roast that developed much past 1st crack. So the problem is too much exit air flow.


I think the best idea is a 4″ duct that transitions to a 5 or 6 inch with an end cap on it …that is, totally blocked. In the end cap I could cobble together the aforementioned adjustable air vent – a circular disc with paired holes that align/misalign to produce varying amounts of exit air flow.

This is sort of my next plan … it doesn’t show the top. I would basically buy 2 end caps, drill the same hole pattern in them and then drill a central bolt through them to rotate the upper disc and create varying air flow openings.


Any ideas? Email the homeroast list about it so we can all read it…


As a side note, after using the roasted quite a bit, I started having a problem with the stock i-Roast chaff collector vibrating loose during the roast. This results in rapid air leakage from the roast chamber and dramatic under-roasting of the coffee.

I needed it to work and did not want to replace parts, so basically I drilled a angled hold through the plastic, bent a nail to form a “pin” that keeps the chaff collector aligned with the glass roasting pot … and voila- no more problems with vibration.

This page is authored by Tom Owen and Sweet Maria’s Coffee, Inc. and is not to be copied or reproduced without permission.