how can I improve a roast in a drum with no airflow?

[maire]

Hello!

I am not a roaster. I've only taken a workshop in roasting, and shadowed a headroaster for a day and read stuff. I'm on the side of making coffee and cupping coffee.

However, I'm at the moment in Nicaragua, volunteering in a cooperative and besides other projects, I find myself looking into some problems they are having with their current roaster.

I spent the weekend cleaning it - green coffee in the shoot, in the chimney, charcoal coffee at places..the cooling tray had never ever been cleaned - I opened the base up for the first time ever, and filled about 1,5 coffee sacks.... They don't roast very often, so I haven't had a chance to see how they actually use it.

Anyway, the roaster works with gas (it's being lit with a newspaper:razz. The drum has no airflow. There are no temperature probes. I'm being told the roasts are 30-40 minutes long and burnt (I wonder if the burning was the question of cooling down, which might work better now). They were told the drum holds 100lbs, but it didn't work, so they were told a new amount of 60lbs.

Besides reducing the amount of green a bit more...what can I do without temperature probes (I have to think for a bit how I can get my hands on something down here...) that would shorten the roast to something more like 17 minutes...or what can I possibly to to have more consistency?

Thanks,
Maire

 

[topher]

Are you sure you can not control the air flow? What is the pipe on top that leads from the neck of the bean hopper? It looks like an exhaust pipe. Can you snap a few more pics from different angles?

 

[maire]

Some more picks

Hey!
Thanks for reply!

That pipe is exhaust yeah...I guess we call it here a chimney...It goes from the neck out to the actual chimney..no flaps or any other things.

The built is a bit awkward because it retains green beans in the chimney! Also chaff stays a bit in the loading tray. There is a hard wire like 'tool' that helps to get the green beans into the drum, but it really works only so-so... When I cleaned the machine I had lot of work to do to get the old greens out, thankfully they had an industrial hoover that helps loads! It's not one of the maintenance tools in the roastery.

There is no fan in any other part of the machine, besides the cooling tray. The drum is really heavy. The only flap that is possible to open is the back-flap of the chimney before the smoke and stuff goes directly up into the sky.

 

[eldub]

Wow. I had to think about this one for a bit before posting any ideas.

I would fire up the roaster and give it about 2/3 gas for maybe 1/2 hour to get it warmed up. Then I'd charge the barrel with green beans and start a timer. I'd cut back on the gas to maybe 1/4 for about 2 minutes and then crank it back up to about 2/3. When the beans reach 380-390* you should hear first crack. Hopefully that will come at about the 11-13 minute mark in the process. IF you hear the first crack in roughly that time frame, decrease the gas to about 1/4 and continue the roast for another 3-5 minutes, depending on how done you want the finished beans to be. Second crack should be going strong at 440*. My goal would be to drop the beans into the cooling tray and hear them popping off in the middle of second crack while cooling.

The first batch will be a shot in the dark. A subsequent batch will go quicker, as the roaster will be running hotter the longer its fired up. That means you could cut back on the gas further after charging the barrel with green beans, but still want to give it gas a couple of minutes after the beans enter the roaster.

If you bring up the roaster temp too quickly after charging the barrel with green beans, they will have pock marks when finished.

Just remember first crack should be going strong at 390* and second crack at around 440* but second crack is more difficult to hear than the first.

Good luck and keep us posted, eh?

lw

 

[eldub]

Btw, if you have no control over amount of gas, charge the barrel with green beans after letting the roaster warm up, start a timer and listen for the first crack. Then keep roasting for 3-5 minutes and drop the beans into the cooling tray.

 

[maire]

Thank you! ...I don't have any way of knowing temperature... But I should be able to figure out the flame...I mean...I think - the smallest the flame goes is not touching the drum, and the biggest it's out of the 2 little doors :lol:

It's going to be some weeks before we'll roast...just the way things are down here...:images:

I'll report back for sure!

(PS. In 6 months time they'll have a Diedrich or Loring...cool, huh?! Should be much easier then!)

 

[eldub]

You will know the bean temp by listening for first crack. The trick will be getting to that point in the desired time frame, imo.

Good luck.

lw

 

[eldub]

Btw, when your bean temp reaches about 300* they will have finished drying and entered the roasting stage. You will notice a wonderful smell at this point that reminds me of an apple pie baking. Hopefully this marker will be reached 5-8 minutes after charging the barrel with beans. If everything is on track, the beans will be heard reaching first crack four to six minutes later.

 

[eldub]

Be sure to take notes and to chart the amount of time the roaster is allowed to warm up as well as the gas levels used in order to be able to reproduce or tweak the results with subsequent efforts.

If you reach one of the markers outlined above sooner that desired, cut back on the gas. if you are falling behind schedule give it more gas. The goal is to reach first crack in the desired time frame and then to back off the gas to let the beans coast to a finish, slowing the process between first and second crack.

Documenting the gas levels/time needed to reach the recognizable stages will help with consistency.

 

[maire]

Two little doors

Yeah, I know that logging all is the god of consistency. :wink:

So I observed today them working on the machine, and...yeah..oh well.... I don't really know what to say, besides that I know that I can help, even with my limited experience! But that's positive, huh?!:-D

:question:One question though - the two little doors by the flame, how much will they effect the heat, what do you think? Open? Close? One open? ...I don't have loads of coffee for experimentation.

 

[eldub]

I'd at least leave one door open to allow you to monitor the flame.

 

[wmark]

RE: airflow, there appears to be outflow, I would hazard to guess you need to be able to create inflow of air