This page composed with Open Office Writer. Best viewed with Mozilla Firefox. Microwave Roasting Questions or comments?
Retirement: 11 years old forever...... 
Microwave Roasting |
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Microwave coffee roasting sounds like a crazy idea. It probably is. At least two commercial products have been tried and abandoned in the marketplace. They were both small paper or cardboard bean containers which rolled around inside the oven. Microwaves can roast too fast to control and continuous mixing is absolutely critical. So given the technical difficulties and the previous failures, who better to try it again than somebody crazy enough to build coffee roasters at home? Don't Do Stupid I'm a retired professional electronics geek with plenty of experience in microwave design and safety. So hopefully I know how to be careful with microwave ovens and how to test for dangerous leaks. I do and I did. Microwave energy is a silent killer. It's not like putting your hand on a hot stove. Microwaves can cause permanent nerve and organ damage before you feel anything at all. CAUTION: DO NOT MODIFY YOUR HOME MICROWAVE OVEN UNLESS YOU HAVE THE PROPER EXPERIENCE AND SAFETY EQUIPMENT. Preliminary Notes This project uses a large (turkey-sized, 1500 watt) thrift store microwave oven, $15 (cheap). I'm trying to do the entire project without modifying the inside metal oven chamber, the door, or any of the standard parts. Anything required inside the oven: 1) must be non-conductive; and 2) must not absorb any appreciable amount of water. In addition, materials in direct contact with the beans must be: 1) food safe; and 2) able to tolerate 425°F or higher. The only modification to the oven itself involves adding an exhaust fan on an existing side vent. The extra fan was required to pull smoke, excess water vapor and combustion gases out of the oven. Roasting takes place in a loosely sealed glass canister which rotates on a special plastic frame. The idea for the frame was not my own, but came from another home roaster on one of the many great web forums for home coffee roasters. One excellent idea proposed and tried on the Homeroaster forum was to place a cup of water in the microwave with the beans. The water absorbs some of the energy and slows down the heating so it's easier to control. The concept is to use something like a half-cup of water for a small batch of beans (100 grams, 3 or 4 oz. by weight), and a quarter-cup or so for a large batch (8 oz). Early tests have been very positive in terms of bean flavor. The general opinion was the flavor more resembled the dark mellowness of a drum rather than the brighter flavor of an air-bed roaster. Unfortunately, using a thick glass counter-top canister was a bad idea. It cracked during a trial roast. Even so, it did hold together and finish roasting the batch. I replaced the canister with a 3 liter Pyrex beaker (high purity borosilicate). As soon as I fashion a new Teflon (ptfe) lid, I'll update the website with new results and a better description of the overall fabrication process.
Final Build The following photos show the addition of the high-temperature 3-liter beaker and Teflon (ptfe) lid. The lid has been cut from a 6"x6" sheet of 1/2" thick ptfe. I used a band saw to cut the overall round shape a little larger than the top lip of the beaker. Then I cut-in the lid edge with a table saw with the blade set only about 3/8" above the table. Commercial beakers are not exactly round. So I cut the lid by tracing the actual beaker rather than a perfect circle drawn with a compass. The lid fits snugly but does not seal the beaker tightly. Expanding air and vapors are free to leak around the edge and through a gap at the pour-spout. Any attempt to contain the gases and smoke would be explosive and dangerous.
Please come back periodically to check for updates. Jim
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