Well to my surprise the work on my drum has already been done. Very happy with the quality of the work.


Ended up making the slots in the outer shell lined up with the middle of the elements. I decided on 40mmL 5mmW.

I have temporarily covered the original air hole with silicone rescue tape (works well) until my silicone plug arrives.
With this not covered it still pulls air quite strong, so i might try a few roasts with it not covered and see what happens. The slots still seem to draw air very lightly with the hole not covered.
So I am not sure whether I have enough opening for incoming air with it covered or too much? I might try covering the 2 front slots to see what effect this has on the airflow.

EDIT: After further testing with the lighter flame. albeit with an empty drum. I can get back to the original pull of air by covering the front 2 slots and the original hole, leaving the 2 back slots drawing the air. As soon as I open up other slots I loose draw and end up with positive pressure bending the lighter flame away from trier hole at my minimum fan setting. I also tried covering all the slots and having the original hole open again and the behaviour from memory of previous testing with the lighter is the same. Probably correlates with TomC successful use of the original hole with the new drum. I noticed the back plate the hole is in is quite thick and gets very hot during a roast, so any air entering through there must be quickly heated coming from normal room temps.
For now I will persist with the 2 back slots.



3 roasts so far, first 2 were no good due to some slight differences in control.

Needed to up my fan settings 0.5 to 1 where I usually adjust the air and use slightly more power.
Much finer control over my charge temp.

By the 3rd roast I matched my previous " baseline " profile with a coffee I am quite familiar with. Initial observations, the roast is visually lighter in color for this temperature and after munching on a few beans (which I generally do after each roast) they seem to me much more evenly developed.

Like TomC I had a similar observation regarding the chaff color, it is light blonde compared to some older chaff I still have in a bin that is golden brown, sometimes tending dark brown.
Anyway, really looking forward to roasting lots more with this new setup. Without going overboard on speculation, my general gut feeling so far is that it is going to be much easier to develop hard washed beans at lighter roast depths.

Thanks for the inspiration this thread has provided.

Very nice work - I'll do something similar!

If I try to summarize what this will do is to make ET and MET track closer together and with less of a lag between the two (that lag made it tricky to control ROR).

I noticed you covered the two "holes" which look like the old area where the air intake was. This is something I modified on my quest to get better use of the air velocity. Covering the air intake does two things. It changes pressure and it changes air speed velocity. Probably some other items but those are the two big ones. So I think you're on the right track with the Rao lighter test method for controlling the forces.

The chaff color is an interesting observation. It's not browning as much...I wonder if your airflow changes simply changed some of the heat xfer forces at work and created a larger convective heating force or alleviated some of the effects of the drum (heat loss needing to really crank up the elements to maintain curve. Thus a very hot drum surface). My only guess (unless it was answered and I missed in my read through) is that greater convective heating is not "straining" the thin chaff under a barrage of heat, resulting in even and subtle changes that don't roast it as much. I hope that made sense. It's 6AM and I'm not even into my Chemex yet...

You did a great job there on everything! I wish I had the time and effort to toss into my Quest like this.

Fantastic workmanship!

Could you post the coffee weight used and fan speed during the three phases?

Are you considering to add baffles on the heating elements like Mr. Bill?

Congratulations on your project! I emailed Molly and linked this thread, with a suggestion that they at least consider this as an option in the future. It would add a negligible cost increase to the Quest and early on, seems to make a significant difference.

It's really surprising seeing how much thinner the newer drums are compared to my original. I'm guessing that the thinner drum is more responsive, but less likely to "coast" thru certain stages of conductive/radiant heat transfer.

The Kenya Gachatha AA is wickedly sweet, like berries and pancake syrup and honey. I'm letting the Ecuadorian coffee rest a few days longer but roasted that for espresso.

TomC wrote:Congratulations on your project! I emailed Molly and linked this thread, with a suggestion that they at least consider this as an option in the future. It would add a negligible cost increase to the Quest and early on, seems to make a significant difference

Would getting Quest with perforated drum be similar to this mod?

Likely not. But everything is speculation at this point. A perforated drum would allow a lot more radiant heat and likely less conductive heat transfer. Having the drum offset from the back wall and a perforated rear wall, it behaves like a larger Probat style roaster now, albeit electrically heated.

I wouldn't want a perforated drum directly over electric elements, that's just asking for trouble.

Thank you for all the comments.

After some more trial and error runs I decided to block up those front slots. Interesting the comments on pressure and velocity changes. It has been a steep learning curve trying to understand the changes in size and position of inlet holes / slots make along with the air now flowing through the drum.

I came to conclusion that having air being drawn at the front and wanting it to go through the back of the newly ventilated drum was having a negative effect overall. I think a lot of the air may have been going straight up and out the chimney through the small area at the front between the drum / faceplate. Front slots are blocked off with some REALLY tightly folded aluminum foil. Along with the new silicone plug in the original hole with a small amount of rescue tape to make it tight fit.

Started using the fire blanket shroud again, just draped over the outer shell. It hangs like a curtain nicely in front of the slots at the back.

Just about ready to roast some higher quality greens after I cup the few successful roasts I eventually had.

I just drilled about 20 holes around the drum (last inch toward the back) and it is simply amazing how air flow changed, how MET and ET trend better aligned and how easier it is to control the roaster and the ROR curve.

Roasted 3 days ago. The difference is substantial in the cup (just switched from the old no-hole batch of Kenya AA to the same coffee w/holes batch dropped at a low 206 and yet fully developed.

I feel dumb for not having done it earlier.

Picture please... Sounds pretty awesome btw