Interesting tip. I would guess it holds up, since there's nowhere for the heated air to go if I'm not venting it, and I certainly get moisture accumulating at the cyclone fan.

Our understanding is that turning the air off during the beginning of the roast allows steam to accumulate. This supposedly provides a better transfer of heat.

This was the most interesting take away I got from watching your video with Joe; I'm planning to do some side-by-side experiments with this when I get home, to see if I can taste a difference (and to see if the difference is beneficial). If I learn anything interesting, I'll start a new thread to discuss it.

I'm not sure if it's taste or tipping or something else entirely.

I read this story in Readers Digest about a million years ago:

Once upon a time, a mother was teaching her daughter the family recipe for making a whole baked ham. It was the very best ham anybody had ever had so they always followed that recipe carefully.

They prepared the marinade, scored the skin, put in the cloves, and then came a step the daughter didn't understand.

"Why do we cut off the ends of the ham?" she said. "Doesn't that make it dry out?"

"You know, I don't know," said the mother. "That's just the way grandma taught me. We should call grandma and ask."

So they called grandma and asked, "why do we cut off the ends of the ham? Is it to let the marinade in, or what?"

"No," said Grandma. "To be honest, I cut the ends off because that's how my mother taught me. I added the marinade step later, because I was worried about the ham drying out. Let's call great grandma and ask her."

So they called the assisted living facility where great grandma was living, and the old woman listend to their questions, and then said.

"Oh, for land sakes! I cut off the ends because I didn't have a pan big enough for a whole ham!"

This has made me suspicious of received wisdom for about 40 years. While that doubtlessly made me a better engineer, it's always made me a bit of a buzz kill everywhere else. ☺

I turned the air and gas off for the charge today, and it worked well. I didn't think the perforated drum would hold heat as well as a solid drum, but it holds it well. I also followed Steve's suggestion to increase load to 1 1/2 lbs. for better heat control.

Added 8/1: Text and photos showing blockage of airflow to reduce fan intensity was deleted because that's a wrong direction, per above.

Here are some plots of today's roasts. I decided to try a faster roast of the Klatch Gedeo Worka. My cupping this morning revealed that yesterday's longer roast came out with nice flavors, but they were muted. In these plots the blue squares represent gas adjustment, the grey is fan. But when I show 30% fan, it only starts spinning at about 20 on the analog dial on my roaster. The digitally recorded numbers don't represent flame height, either. I'm getting a feel for that also by visual observation, noting that even a very low flame setting isn't that much proportionally smaller in the actual flame. This isn't very different than cooking with a gas stove. You look at the flame rather than becoming too fascinated with the dial.



Here's a Sweet Maria's Brazil Fazenda Junqueira Reis. I'm roasting it longer to emphasize chocolates.

I would be surprised if your perforated drum roaster's environment temp couldn't be controlled like a laser, fast and responsive with gas changes alone. But I wouldn't bog down with concerns about airflow control. It likely lacks any semblance to any standard drum roaster in this regard. CO2 fire extinguishers work on a similar application by which your plugging off most of your roasters ventilation. I can't see any reason why this is a good or ideal approach. You're suffocating your fire, likely decreasing your heat output, and choking your blower. I'm sure the motor on the blower will not appreciate that level of flow restriction for very long. And you're changing the basic fundamental design or the whole system, who knows what any increased water condensation will do over time to various components.

I agree with Steve's suggestion to just increase your charge load, and then learn to control the roast via heat modulation based on that.

Gary may I suggest a different approach regarding the airflow?

This is something I've learned from visiting Coffee tech's factory in Israel, their small roasters (1 and 2.5kg) have perforated drums and I was told that airflow on these roasters should be kept minimal as possible throughout the roast in order to achieve more conduction.
The roasters have an automatic controller that opens the air on max for 5-6 seconds every 2 minutes or so just to clear chaff mostly.

I know that the TJ-067 designed differently and this may not apply to it but I suggest you give it a try and see if that works.
I have managed to successfully implement a similar method in the Huky but with a smaller 1 minute interval.

Kfir.

Good suggestions from Tom and Kfir. I'll have to play with this at a full Kg. But if I do that I'll have to start a coffee business (not). I'm finding that 1 1/2 lbs is better. I would like to master it at lower charges. And I'd been thinking about techniques more like the one Kfir suggests, a burst of airflow, then gas. I can also open the bean chute incrementally to dump some hot air. I did notice in yesterday's roasting that heat was more stable after I'd gotten into the third load. Before charging, I had the BT readout at about 370F and was looking for 350F. If you look at the plot you'll see I incrementally started and stopped the fan to get it down and it kept climbing up with the fan and gas off. I'll need to give it more time for heat to permeate the machine.

To Tom's concerns about putting wear on the fan motor and accumulating moisture, so far I'm not worried about either. After yesterday's roasting session there was no residual moisture in the roaster. I'm using the fan minimally at low RPMs. The more limited venting in the roasting chamber is preventing the flame from being disturbed by a breeze that can come into the garage door of my outbuilding. Let's keep in mind that my roaster is not a standard TJ-067. I had to push Tim to build it with a perforated drum when normally that's only stock equipment in their electric version.

I'm going to play with it some more. Anyway I'm happy that at this point I've got it under better control.

Gary, I think your roaster has the same design as mine except for the perforated drum..
On mine the burners flame tips is right on the drum of my roaster..

I would take the drum to a welding shop and have them MIG weld the holes closed..
It would take 10-15 seconds per hole to weld them shut..
It is not a big job if you can find a small enough shop to take the job..

To go over the top you could have it wrapped in a copper sheet metal jacket and make it like a one of those custom double walled drums I seen in books..

That's a good last resort and cheaper than getting a replacement drum, which would cost upwards of $1K.

But for now I'm getting good roasts and want to play with the perforated drum version and see if I can get it tuned for my use. This could involve trying a smaller fan motor too. There's also the possibility of placing the ET probe lower in the chamber.

No matter what the ET readings, I'm able to control the roasts pretty well already without any more mods. At this point I'm learning how to allow more rising temp in the vicinity of 1C and beyond, which is perhaps the hardest part to control. You can see a slight dip in my curves. I think short bursts of fan balanced with application of heat will do the trick.

Gary,
Something I just found out is with my roaster on it's wire cart at last and off the dolly just off the floor, the exhaust hose is longer with more sharp bends I don't get the same flow as I did with a straight shot to the cyclone.. If you can add a bend or two in your flex pipe it may give a little lower flow..

Side note on double walling your drum.. It maybe cheaper and better to use stainless steel sheet metal than to weld the holes shut..