Benti Nenka Beans falling out after 1 min of roast time!

I just bought a 50lb bag of Ethiopia Dry Process Benti Nenka from SM’s. Aside from being little tiny baby beans :kissing_closed_eyes: I ran into an issue during a couple 750g roasts today where about a min in the beans just started tumbling out of the chaff shoot.

Anyone have any experience with these beans? Or a similar VERY small bean size that wants to escape during roasting sessions?

Additionally, FC is almost imperceptible on this particular bean. I can always hear FC but this one is practically silent.

Just to clarify: When you say the chaff chute, are you referring to the area that I have higlighted with a red rectangle?

If so, you might have to adjust the spacer washers behind or in front of the bearing that is next to the trier to reduce the gap.

What @billc said. It takes some fiddling with the thickness of the shims on the end of the drum. Those shims adjust the spacing between the outer front edge of the drum and the face plate. And it’s very fiddly. It’s a balance between enough clearance to not scrape the faceplate and too much clearance which allows small beans to drop out the chaff chute. Sometimes a small bean will get caught between the drum and the faceplate which then pushes the drum to the rear (that scenario is accompanied be a lot of scraping noise!).


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Thanks guys! that’s exactly what I was referring to and I’ll go ahead and try to make some adjustments. Appreciate it :facepunch: :fist:

When I first took my machine apart to clean the IR sensor, I found this happened even with medium sized beans. The gap between the drum and the front plate can be adjusted by hand: with the roaster cool, open the bean chute door and grab a fin, and pull forward. It might not feel like it moved much, but you can tell by looking at the spindle extending from the front panel. Even a mm can make a difference. I have not had to do anything with shims (yet).

For the current hardware version of the Bullet, the drum is spring loaded and will always push to the front and be stopped by whatever shims you have in front of the bearing.

You can check this by pushing on the shaft of the drum it should move back a small amount and then when you let go, it should move back forward.

Something that nobody has really talked about regarding this problem is thermal expansion.
All materials have a thermal expansion cooefficient.
For stainless steels, the average is about .000017 which coorelates to a growth or shrinkage of .000017 of an inch for every degree of change.
So, if the drum is 14 inches long and the starting temperature is 70 degrees F and we heat the drum to 400 degrees F, we could see a linear growth of .04 inches (or about 1mm)
This is the reason that sometimes the Bullet starts scraping and rubbing after the drum gets hot.

I don’t know if the entire drum gets up to the same temperature as reported by the ITBS. It may be that the main shaft of the drum does not get that hot.

The design of the Bullet is such that the thermal expansion should not be too much of a problem for setting and maintaining the front gap. The drum is spring loaded pushing towards the front of the Bullet and and the bearing and shims. Therefore the length of the drum from the bearing to the inside front face is probably less than an inch.

But if the shims are set incorrectly and the bearing housing and bearings near the chaff collector aren’t set correctly, then the growth might create unanticipated pressure on the back bearing housing and cause problems.


Gotta love having all the hard core engineers here :slight_smile:

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Good to know Dylan – I actually need to clean my IR Sensor so I’ll handle both while I have the faceplate off.

Interesting, I didn’t know that. Thanks for the heads up!

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I hope you’ve read this, but there’s no harm in linking similar threads.