The chaff cyclone

The chaff cyclone

Separating the beans from the chaff...

We've discussed coffee bean processing in earlier newsletters.  You'll recall that we need to remove the cherry of the coffee bean in order to get to the seed which is what we heat to end up with delicious roasted coffee.

There is a layer of material in between the cherry and the seed which is not removed by coffee processing... referred to as the skin or parchment.  This comes off as chaff when the beans are roasted.  Commercial roasting machines use a chaff cyclone to remove the chaff so that exhaust flues don't fill up with chaff and cause roastery fires.

The physics of chaff cyclones is really interesting and is dependent on cyclonic separation.  Exhaust gases exiting the drum roaster are accelerated in a helical pattern by the exhaust fan and a combination of centrifugal force and gravity allows the chaff to be removed from the rotating column of air.  The chaff possesses too much inertia to follow the tight curve of the air flow created in the cyclone and strike the wall of the cyclone and fall to the bottom of the cyclone where they can be easily removed.

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