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Hottop Coffee Roaster Drum Mod for Bean Agitation

April 25, 2010

Regardless of roasting parameters and batch size, I was still struggling with charring and tipping problems on some softer coffees (like Brazilian) with my unmodified Hottop KN-8828B Drum Coffee Roaster. I tried decreasing the batch size to 6 oz to allow for a lower environmental temperature, as well as using the fan throughout the roast for more convection. These changes helped, but a small percentage of beans would still exhibit a little tipping.

Inspired by Ed Bourgeois (“farmroast”) and Max (“coffee.me”) on the http://www.home-barista.com coffee roasting forum, I decided to modify the roasting drum by adding a couple of additional “fins”, to allow for more bean agitation. The stock drum already has three small fins, but their purpose seems mostly to drive the beans out the chute when you eject them, not agitate them. Here’s a photographic step-by-step to what I did:

1. Mocked out the pair of fins in cardboard, mostly to have an idea where they’d need to be notched to clear some of the existing hardware in the drum. Then transferred this template to an old aluminum toaster oven tray, because it’s what I had on hand that would be easy to work:

2. The roughly fabricated fins, with markings indicating where they could be drilled for mounting hardware:

3. Attached using stainless steel sheet metal screws:

4. The finished result, new fins are slightly lighter in color at 9 and 3 o’clock:

And here it is in action. Shoulda taken a ‘before’ video as well, but this is a significant amount of added agitation:

The video is of my first run with the modification, an 8oz batch of Sumatra. There was no signs of tipping or charring. Woohoo!

One thing worth mentioning: with these larger fins in place, a small percentage of the beans take an extra 10-20 seconds or so to finally clear the drum when you eject. Seems the beans “hop” over the smaller stock fins that are intended to drive them towards the ejection port. Not a big deal, but somewhat annoying. A potential worthwhile mod might be to install the fins at a slant matching the stock fins, so that doesn’t occur.

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4 Comments
  1. Sweet mod Rama. I bet an angled install would have required many more “cardboard attempts” to get the shape right.

  2. Will T. permalink

    I’m curious: Are the stock fins visible in the step 4 photo?

  3. @willT, they’re partly obscured, but they’re super small too. That was the problem.

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