I've been roasting coffee for a couple of years now, and I've always used a popcorn popper. I'm interested in taking things a bit more seriously and would like to be a bit more meticulous when it comes to roast level. I find that my popcorn popper (1200 W) roasts coffee a little too quickly, to the point that it becomes difficult to get a precise and consistent roast level from time to time. Does anyone know of anyway that I could reduce the power of the roaster? If it roasted at a lightly slower pace I feel like I would have better control over the process. I've heard people suggest plugging it in through an extension cord or a power strip, which will reduce the power going to the popper. Is there a more principled or controlled way of doing this? Some sort of device that goes in between the popcorn popper plug and the outlet that would let me adjust the power at a fine granularity would be ideal. Does this sort of technology exist? Perhaps a sort of light switch dimmer would work?
Rather than playing with electricity and wiring you could actually just move the roasting bed/area away from your heat source and accomplish close to the same thing.
I started roasting with a popper as well. The hole in the popper was roughly 3 inches so I got a 3 to 4 inch duct adapter, a 4 inch flour sifter and mushed it all together, similar to this. The result was that I moved the coffee away from the heat source. The sifter also allows you to stir and get more even results. I think I went from 4 to 5 minute roast time to 7 or 8 minutes with this method and the parts were very cheap.
I believe the forum post for that picture actually has additional mods close to what you may be looking for if you actually want to take your popper apart and try rewiring it.
I'm a little surprised that you need to reduce temps on a 1200watt device. I had the opposite issue but similar techniques might help you. I looked at the system as having 3 basic variables: temperature, airflow, and volume of beans. Alter any one and you can achieve a different result. In my case I was unable to achieve high enough temps with my Air Crazy; particularly in cold weather since I roast outside. This is what I did:
1) Change the thermostat. I did it to increase temps but this is how I'd achieve a lower temp also. I switched the thermostat on my Air Crazy popper to increase the temp at which the element was turned off. If you pull it apart there is likely a thermostat on the chamber that opens the element circuit. It should be marked in some way to indicate it's properties. Mine was riveted on. IIRC I bought a higher temp thermostat and also spaced it off the chamber a little. I used small stainless machine screws/nuts to reattach.
It's going to have 120v passing through it so make certain it is secure and the terminals are not contacting/energizing any other component like the actual roasting cup or popper case.
If you do not have thermostat of some type in your element circuit (you almost certainly do) they are readily available online in a large range of temps. I believe mine opens at 210C now; I think it was 180c when I bought it. 210C is pretty hot and the whole popper gets rather hot but it works for me. You need one that resets, not a single use piece.
I think these are what I used as I have 2 in my desk drawer right now.
In your case if you need to reduce the temps you may try thermal compound for CPU fans or a similar substance to increase conductivity and contact area at the thermostat, possibly turning off the element at a lower temp. If not they clean up easily.
2)I altered the airflow also by closing some of the vents on the popping chamber, I've forgotten if I did this prior to upping the temps. Same amount of air through fewer louvers resulted in higher velocities. Mine has louvers on the sides creating a swirling airflow to agitate the beans.
3)I added mass to the bottom of the popping chamber in an attempt to stabilize the overall temps. A few layers of heavy foil tape were enough.
4)I attached screens (actual window screen pieces) to intakes on bottom of it to stop the chaff from entering and burning on the element. I credit this for the 2 yr of usage I've gotten from this popper. Other elements have burnt open much faster.
5) I played with volume of beans to find max I could do without having uneven results. Too much and airflow was insufficient, too few beans seemed to greatly affect the quality.
In current practice I usually need to manually shake the popper every 20 sec or so up to first crack, from there the dried beans circulate well. I like very dark roasts so I also often restrict airflow somewhat later in the process by pressing the popper into a thick towel. It is the easiest way I know to alter airflow (and thus temperature) on the fly.
This was several years ago so memory may be inaccurate. I'm not currently with the popper but can get it if you want more info or pics. I should buy another and better test these methods individually.
I've wired a dimmer switch to my Presto Poplite in series with the heating element to controllably reduce heat. Slowing the roast has greatly improved consistency and flavor.
I used a 1000W-rated dimmer switch. There wasn't room inside the popper to install a wall-mount device so it's in a small electrical box in-line with the power cord.
The popper has a split heating element with one part doing double duty as a voltage-limiting resistor in series with the fan motor. Since the fan needs to run all the time, my dimmer only controls the other ~2/3 of the heating element so it's not possible to reduce the heat all the way to zero. But I'm happy with the outcome.
My biggest process improvement, however, has been manually stirring the beans. With this particular corn popper, the power of the fan is such that forced air circulation doesn't start working well until the coffee beans have expanded, and I dealt with multiple batches of scorched beans along the way to figuring that out.