I followed Max's and Ed's advice, and added some fins to my Hottop drum, along the lines of what Max first detailed here: Charging at a High ET without Tipping/Scorching/Charring?

It's still early to call it, but it seems like a winner! Here are the details on how I did it, for those who might want to give it a go:


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. Ya, they're crude. Its what you get from working with tin snips and a bench vise.


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. Should have taken a 'before' video as well, but this is a significant amount of added agitation. Some beans are ricocheting off the central axle, although you'd never know it from this piss-poor video:



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. I might try this as a v2.0 at some point if it becomes problematic.

One last thing, if the additional fins made things noisier, I didn't notice. Discerning first crack wasn't a problem at all.

Most excellent, Rama! You did a very neat job; thanks for sharing this.

The ones I did were about an inch high, similar location to yours but were slanted along the original fin lines. I still get delayed ejection of some beans but it's nothing compared to the huge improvement on the roast results I got from the better agitation.

If you ever get to v2, can I recommend that you increase the hight of the fins? To my not-fully-functioning eyes, it looks like the fins you installed are less than 1/2" high -- not much bigger than the original ones. I say this cuz of the resultant agitation on your video; it's much weaker than what I get with 1".

rama wrote:There was no signs of tipping or charring.

Yeah, that was a very pleasant surprise to me too. Even with high element power, the extra agitation somehow mitigates grilling of the beans; which is a real problem on a stock Hottop.

Nice job Rama!
I think the fin design on the best commercial roasters is very well thought out but on homeroasters is a detail that is skimped on and kept simple.

coffee.me wrote:The ones I did were about an inch high, similar location to yours but were slanted along the original fin lines.

I was thinking that with fins that ran the length of the drum, slanted fins might push all the beans to one side of the drum. Is that not happening with yours?

coffee.me wrote:If you ever get to v2, can I recommend that you increase the hight of the fins?

Sounds good. Their height was completely arbitrary, they are about double the height of the stock fins. Given the RPM of the drum, it seems unlikely the beans could sit around long enough for any tipping to occur, even with these shorter fins, but adding more height would probably help and would be trivial to do when initially fabricating them.

More height may or may not be an improvement. Keeping the beans evenly spread and flowing diagonally back and forth might be the next thing to consider.

Hmm- good point Ed. Perhaps the fins should be installed in opposite sloping directions. You'd still have the problem with beans not clearing quickly on eject. IIRC, the Probat sample roaster addresses this by being hinged, and you tip them to dump the beans. I guess you could do the same with the Hottop and a pair of oven mits.

Sorry, it's been a while since I did mine, I should've checked before posting . I looked at them again and they are slightly sloped to flip the beans in opposite directions too (i.e. only one matches the OEM fin slop). The result is a bean mass that tumbles both vertically and horizontally. Ejection does indeed take a while to complete but I'd say that most of the load exists instantly. The rest exits eventually but the amount of beans and the time they stay never motivated me to do something about it.

On fin height, with 225g, 250g, 300g loads, 1" is all good. I've not experimented with anything other than 1" so I can't confidently recommend anything else; but I see more agitation on mine than what I see on the video above. That isn't to say you must replace yours, no one knows the right size except people who compared different heights, anyone?

All in all, I consider this mod to the Hottop for better agitation as important as adding BT/ET probes to it.

Any Thoughts on 200gr loads and below? Like say, down to 170gr?

While I never thought about adding fins, the one thing I would say here is that aluminum is reactive to common cleaning agents used to clean coffee equipment of this nature (Cafiza, TSP, etc.). I ave one drum that has been dipped in strong solutions of that type at least three times and it looks new. The cleaner tends to affect the aluminum and deposit on it as well, so those added vanes may need to be removed for cleaning if Brazil with a TSP follow is not to your taste preferences.

JmanEspresso wrote:Any Thoughts on 200gr loads and below? Like say, down to 170gr?

You mean doing 170g batches with the added fins? I haven't tried it yet, but have no reason to believe the fins wouldn't benefit any batch size. Smaller batch sizes might be a bit noisier though, with more beans impacting the drum as opposed to other beans, but I don't think you'd have a problem hearing the crack stages.

Randy G. wrote: While I never thought about adding fins, the one thing I would say here is that aluminum is reactive to common cleaning agents used to clean coffee equipment of this nature (Cafiza, TSP, etc.).

Yes, good point. If you roast to the point that you drive oils to the surface, this is probably a bigger deal. I never do (except the one time the Hottop refused to eject!), so my drum hasn't required a cleaning yet.

Even so, I'd have preferred using stainless steel if it were readily available...