Perforated Drum test and learn - what has worked for you

[yukoncornelius]

Edtbjon has written some very valuable findings about the solid drum configuration (charging lower, etc etc).  I think it would be helpful to have an ongoing thread where individuals post their "light bulb" moments when trying various things on the perforated drum configuration.  Would love to know everyone's experience with altering charge temps, airflow, gas at various points in the their roasts while using the perforated drum configuration.  I'll start with some of my recent findings.

General details for my roasts
Charge weight - 350g is my go to batch size. 

Grate below drum - I always keep the "damper grate" or "shutter" under the drum closed.  I used to mess with this but its another variable I don't want to play with.

Charge Temp - 375 to 425, I'm really not sure whats best for the perforated drum, would LOVE input here.  I do know that obviously lower charges result in lower turning points.  It also seems that if I want my dry phase to be under 5 minutes, I HAVE to charge higher.  I've tried cranking the gas for extended periods and struggle to get the dry phase under 4:30.  Again, I'm not sure how big of an impact it is to have a TP at 185 vs 210F.  I've recently just been charging at 380F.  Maybe that's too low for the perforated drum? 

Airflow - I utilize a variac (0v to 130v settings) with the pipe damper full open.  My general airflow works like this.  During dry phase, up to about 280F, my variac is set to 40v.  At 280ish F, I go to 50.  I then slowly work my way up to 70V, usually in increments of 10.  I get to 70V by about 355 or 360F and don't touch it after that.  I see alot of discussion around minimal or zero airflow during dry phase.  WHere are you guys at?  Makes me think 40v may be too much air, which is why I struggle to get through drying phase at sub 5 minutes.

Phase Lengths.    I've been getting to 300F at 5:30 - 6:00.  Usually closer to 6:00.  Maillard is then around 4:00.  I've been hitting first crack at around 9:30 - 10:00.


Energy into development. THis has been a recent development which I really want to explore.  I don't worry about constantly declining ROR.  In fact, my maillard phase looks pretty flat, and it will even rise.  I've started letting ROR drop naturally, based upon energy built up from my dry phase.  I then use maillard to set up the point I want to hit first crack at.  Increasing heat through maillard, setting myself up for hitting FC at 22F has resulted in reduced acidity, and much more sweet, developed tasting coffee.  The more I play with this, the shorter my dev phase becomes.  My development time ratio is almost always under 17% now.  I try to eliminate the FC crash by bumping heat before FC starts and try to have an average ROR during dev at around ~14-15F/min. 

30F / 22F / 14F is what my phases generally average out to be.

I literally can smell the sweetness in the air once I've started roasting like this. 

What is working for everyone else?  I need to make it a habit of posting my profiles on here as I continue to experiment with different concepts. 

[Jayel]

Thanks for starting this thread. I've been wanting to discuss stuff like this for the perf drum for a while. I too would like to know more about other users' charge temps.

Charge Temp:
I usually charge at 250C (482F) but I've noticed a lot of people charging much lower. I just roasted a pound of black honey process coffee and didn't know where to begin but someone said they had a good roast charging at ~160C (320F) so that's where I started. The TP was ~65C (149F), I didn't get to DE until almost 8 minutes, and the whole roast was ~14 minutes long. ROR was almost flat throughout the roast and I can confidently say this was a waste of good beans. I don't even know where to start next time, I've mostly roasted washed coffee so far and I'm ~80 roasts in.

Airflow:
I've only had a variac for the past 5 roasts so I haven't played around too much but I've been starting at 40V, increase to 45V at ~160C (320F), then 60V just before FC. I keep it there until the end of FC which is when I turn it up to 90V until drop.

Phase Lengths:
My phases are all around 5 minutes, 4 minutes, 2 minutes. Give or take 30 seconds. I have been hitting FC between 8:40 and 9:15.

Energy into Development:
This is something I have trouble with, I always seem to go into FC with just a little less energy than I planned on. I never increase my gas throughout the roast though, I give it enough heat in the beginning then lower it throughout. I usually crank the Gas to 5 kPa 40 seconds after charge then start decreasing around 170C (338F). Dealing with the FC flick is pretty hit or miss with me.

I have recently made a lot of changes in my roast routine (larger batch size, keeping grate closed, and using a variac) so I'm sorry if I wasn't much help. I will say that the one thing I truly believe works for me is the high gas at the beginning and only lowering it throughout the roast.

[hankua]

Good discussion!

You need to be careful about trying to copy a solid drum profile or strict adherence to "Rao" or anyone else (unless they have a perforated Huky LOL)

The reason for this is Conduction vs Convection; both are going to be different with the perforated drum "direct fire" in the Far East.

Your convection is totally different, and the drum is going to absorb/radiate less heat than the solid version. In theory you should be able to achieve more development in a shorter period of time vs my solid drum setup. That could by why using more gas/air works?

[SusanJoM]

Here's a perforated profile.

I never close the grate and I have replaced the variac with a simpler controller (adjustments are only 3 variants on low, medium and high).

Hank put his finger on a big issue:  low charge temperatures seem (?) to work for the solid drum, but NOT for the perforated drum.  The perforated drum doesn't hold and then transfer the heat (no one with a perforated drum has ever reported any tipping or scorching, for example).   Get the HUKY good and hot (have some air going and the drum turning while you warm up at a nice low gas setting;  then crank the gas to maximum as soon as you drop the beans so that your load recovers from the arrival of all those relatively chilly beans.

[Jayel]

That's a great looking profile, thanks.

Yeah I will never charge that low again but I do want to experiment going a little lower especially with these black honey process beans. What is the lowest you have successfully charged?

I also like how you have simplified your airflow adjustments as well. I try to stick to only 3-4 settings even with the Variac.

[SusanJoM]

What is the lowest you have successfully charged?

Probably about 440F

I also like how you have simplified your airflow adjustments as well.

Hank's advice when I started roasting was to find the simplest possible route to the desired roast.  I often roast without making any changes to the air flow at all..