|Perforated Sheet Metals Used in Home Coffee Roasters
Here's some information to those interested in building their own home coffee roasters, especially drum type roasters to be installed in gas Barbeque grills, what hole-sizes and patterns are used in the currently available coffee roasting appliances. Here are some images, and all should be at the same scale, although they are not "actual size":
|1. The Alpenrost Drum is unique among these samples: it is the only one desiged to allow chaff to fall through it while roasting! Notice the percent of open space to metal ... this is highly perforated. The holes measure just a hair over 3/16 inch. It corresponds somewhat to McNichols 3/16", 1/4" staggered centers, 18 holes PSI, 50% open area (although it looks even more open than this, more like samples with 60-65% open area)
2. The bottom of the Hearthware Precision Roast Chamber has 2 hole sizes. The smaller hole is 5/32 " and the larger is 3/16, same as the Alpenrost. This is a little suprising since the function of of this roast chamber is not to allow chaff to pass down through the roast chamber and fall down into the base. But with such a positive air flow upward, this is not much of a risk.
3. This is the ring from the interior of a well-used Hearthware Precision Chaff Collector. This hols size and pattern is identical to the Zach & Dani's coffee roaster's roast chamber bottom, but I couldn't get a good photo of that. The function here would be to hold back chaff, but allow air flow. It is approximately 1/16" holes and corresponds to McNichols 1/16", 7/64" staggered centers, 98 holes PSI, 30% open area
|4. This is an image of the Coffee Kinetics 1 Lb roaster's roast chamber bottom. This roast chamber is like any of the smaller air roaster chambers (Freshroast, etc) in that a strong air flow comes up from the base ... so the function is to hold the coffee and resist letting chaff drop down (although air flow prevents this too). These are 1/8" holes and corresponds to McNichols 1/8", 3/16" staggered centers, 33 holes PSI, 40% open area
5. This is the Freshroast roast chamber bottom, and they appear to be 5/32" holes with a much greater open area than the Coffee Kinetics (But the CK roast chamber diameter is about 8-9" compared to about 3" on the tiny Freshroast). This material corresponds with McNichols 5/32", 3/16" staggered centers, 33 holes PSI, 63% open area
6. This is not perforated metal, it is a screen, and its from the top of the coffee kinetics. All manufacturers are using screen for places where they want air to pass, but all chaff to be trapped. Freshroast Plus has the coarsest screen, HWP is very fine, and the Zach & Dani's, in the top piece, has an extremely fine screen.