I am somewhat new to home roasting (having cut my teeth on the original Behmor 1600), but recently found what I perceived to be a good deal on a custom-built drum roaster. This roaster was built for a coffee shop who roasted their own beans for a few years with it, but they finally outgrew it. It is a well-built, heavy machine, and was ADVERTISED as a 1kg unit. However, based on drum size and comparing that to, say, RK Drums, I'm wondering if it might have a slightly larger capacity. The drum is 15" in length by 9" diameter.

Question 1: based on the 15" x 9" drum, does a 1kg load sound right? (A "4 lb" RK drum is only 12" x 8".)

The unit is a propane/natural gas burner. It's lit electronically by a RobertShaw commercial pilot light re-light system. The drum is driven by a 110v Dayton shaded pole 1/20hp gearmotor turning at 30 RPM.

My more pressing question has to do with airflow (or possible lack thereof). I'll post pictures below to help illustrate, but as I've read other posts on this forum, the main drawback of, say, an RK drum set up is the LACK OF AIRFLOW. The design of this unit does not have a fan, but rather convection-based air movement... cold air intake low on one side of the unit, then a chimney up high on the other side. Here are a couple of exterior views of the unit (excuse my messy garage):



Hopefully those two pictures help paint a visual image of the main design aspects of the roaster. I'd now like to give a better view of the perforated air intake in the lower-right of the picture above. This happens below the motor, and right by where the main gas line (pipe) enters the interior of the roaster:


As you can see, it's a pretty basic needle valve gas control with a perforated (and "hooded") fresh air intake right above it.

If we look INSIDE the unit where the gas line comes in, we see this:


Hopefully all of these pictures help establish a clearer picture of the roaster's design.

Now, inside the unit, there is about 4" of "dead space" or free space between the wall of the roaster and the drum:


And then another more zoomed out view showing the interior of the roaster (with the chaff tray pulled slightly out):


To the front panel (my very first picture), I will be adding a BT and ET probe that feeds into a Phidget/Artisan. I MIGHT also add a probe for exhaust temp and/or flame temp, but I'm not sure that those will be as valuable. This leads me to:

Question #2 (and a rather open-ended one at that): is there any "low hanging fruit" that could improve the design of this? For instance, would the addition of a fan help this unit out, and if so, where should that fan be placed? I have a convection fan from a full-sized oven that I could use to simply introduce air MOVEMENT into the roaster... but that wouldn't pull in more CFM of air. It would simply move around the air that already naturally flows through the unit. That 4" of "dead space"... is there something that this space could be used for? A fan? A larger drum? Or is it perhaps a design element that helps mix/equalize the cool outside air coming in from the perforations?

Based on the striping of the drum unit, it looks like there has been some inefficient combustion, so I will tune the air mixing of the gas supply to remedy that. I might also put more of a heat shield between the flame tips and the drum to avoid hot "stripes" along the drum. I will say, however, the the drum is made of quite heavy material... I believe 1/8" steel. I think this will help buffer the heat from the flames.

I'm basically hoping that someone had experience with roasters similar in design to this that might be able to give me advice. I'm thinking that this design must be based off a commercial design of some type, but I don't know what that would be. Any comments/suggestions from the collective knowledge base here? Thanks in advance!

There are a LOT of folks who have built their own roasters at www.homeroasters.org You might try there.

Thanks Randy! I had never heard of that site. However, wouldn't that be the definition of cross-posting that this site warned me about in big red letters?