Prototype Testing – Part 1 : Roasted Coffee

2011 July 15

We finally recovered from walking pneumonia and were able to get back to active work on the prototype. It had been waiting for us at AMCE Metalworks for about four weeks.

We headed over to ACME with a trailer and had them fork lift it into place.

We then transported it to Agritopia, where we used one of our tractors to fork lift it out.

The prototype was then moved into our test facility. We clamped the water jetted return vane strip into place using long reach C-clamps. They were positioned at the margin between each vane. Due to the variable gap and run out between the bowl and the support ring, we fashioned a heavy paper sleeve/gasket to make sure no beans leaked out once the bowl began to spin. As mentioned in earlier posts, the gap and run out problem is a result of unrelieved stresses in the original bowl that manifested themselves when we separated the bowl from the ring.We bent the return vanes into place so as to direct the beans back to the center of the bowl. At this point, it was time to do an initial test, so we put 5 lbs. of roasted coffee into the bowl.

We slowly increased the speed of the motor and as we did, the band of beans crept up the side of the bowl. At about 90 RPM (bowl speed), the beans started to contact the vanes and flowed back into the center of the bowl. Obviously, we were very pleased that the prototype was working well right at the start.

The next step was to go to a larger batch size, in this case 15 lbs. of roasted coffee. That is approximately 1/2 of design capacity. We also began refining the shape of the return vanes for improved performance.

The vanes are designed with tabs to be fashioned into a compound curve. The revised shape did a better job of directing the return flow of the beans.

This test ran very well. A video of the test is shown here: ProtoRun1 – Computer

Over the next couple of weeks, we will  running various batches of roasted and green coffee. During these tests, we will be using both strobe and HD video to observe bean flow, analyzing to see where we can make improvements. The optimum bowl speed for various loading and densities will also be ascertained. We will also attempt to source some cacao to make similar tests. After that, we will add variable airflow from an overhead jet.

We are highly encouraged and feel confident that the bowl roaster approach is sound.

3 Responses
  1. Keith P permalink
    July 15, 2011

    Hands down, this is cool! I had a handle on what the concept was based on reading the blog, but nothing beats seeing it in action. Just less than 11 months until my test batch, Joe. I’ll keep you to it!
    Thanks, also, for posting a downloadable video. Seeing as how most online video sites are blocked at my work, I was still able to view it in action.

  2. chaoss permalink
    July 20, 2011

    Very nice design.
    I know that you have taken into account that green beans (unlike roasted, in your test) carry a greater density/less mass signature. That said, your VSM will come in very handy when calibrating/programming for various roast profiles.
    Also, one would think that the less time that the bean is actually in direct contact with the bowl (free floating like a popcorn popper) would be ideal for an even & consistent roast.
    Looking forward to your green test results.


    • July 21, 2011

      Our testing with green beans has found that the optimal rotational speed is very similar to the roasted coffee (about 90 RPM). As for contact, the mixing is vigorous and when we add convective airflow into the next round of testing, I think we will get some “floatation”, as well. So far we are encouraged. Thanks for your kind comment.

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