Air Popper Modifications -Adding a Thermometer

We have an updated page dedicated to this same subject, Adding a Thermometer to a Coffee Roaster or Air Popper, which includes this video Tom made:

… but we wanted to preserve the old-timey information about using a dial face thermometer to measure the ambent roast temperature too. You could modify a popper to do both!

Adding a Dial Face Thermometer to your Air Popcorn Popper for coffee roasting

A thermometer can help you establish a more consistent roasting routine. Adding a thermometer to your air popper measures the temperature of the forced air heat flow after it has passed through the beans. Therefore, it is neither an empirically accurate measurement of the bean temperature, nor of the roasting chamber.

That means that a person roasting in Chicago with a UEI brand thermometer in his Popcorn Pumper and someone from Tulsa with a Pelouze thermometer in a Poppery II cannot accurately compare their roasting notes. But it does mean that the first person can observe that his Sumatra reached a higher final temperature in 5 minutes than his Harar, or that 2 ounces roasts hotter than 3 ounces, etc.

(Also see our newer article: Digital Coffee Bean Temperature Probe for an Air Popcorn Popper)

A. Thermometer mounted in butter cup dish (old air popper)
B. Thermometer clip holds it in place
C. Shaft extends into chamber 1 inch to 2 inches from bottom

We sell a Update Brand pocket type thermometer which is a good value. It has a 5″ shaft which makes it ideal for the Whirley-Pop and adequate for the air poppers. As the beans lose their moisture and begin to rise, they meet the 5″ shaft and your readings will be accurate. It’s always in the airstream, anyway. The 400 degree candy/deep fry thermometers are widely available too but I don’t like extrapolating the measurements between 400-500 degrees, since that’s where temperature is critical. 500 degree thermometers with longer shafts are available, and would be ideal for the air popper but they are prohibitively expensive.

The easy way to add a thermometer is to consult Ken Davids book, Home Coffee Roasting, and follow his instructions: basically, you drill a hole in the plastic popper hood at the exact center of the circular roast chamber and drop your thermometer into it. Simple, eh?

Air Popper Modifications -Adding a Thermometer

Yep – standard disclaimer: If you choose to alter your air popper you are assume the risk that it will no longer work as it was designed to, that it might not work at all, that you might injure yourself in performing these tasks or in using the altered device. This information is here for you to peruse, but Sweet Maria’s accepts no responsibility in what the results may be.

We found that this installation method, with or without the thermometer clip, made the thermometer wobble around a lot in the air stream and as the beans came into contact with the shaft. One possible variation is to simply fix the thermometer to the hood with the RTV type sealant mentioned below. But we like to remove the thermometer to use in our other roasters, or for cleaning.

So we searched far and wide for some sort of metal fitting, ideally a sort of collared bearing with a locknut to keep the thermometer in place, but allow for its removal. We couldn’t find anything that would fit the bill. So we compropmised by modifying a common fastener called a Tee Nut, and adhering it with high temperature RTV sealant.

What you need:

  1. 8/32, 9/32 or 10/32 Tee Nut -local hardware store
  2. High Temp RTV Sealant -auto parts store
  3. Drill and bits: possibly 5/32, 7/32, 15/64, 1/4, details below.
  4. Wire snips or sheet metal snips

What to do:

  1. First of all, Tee Nuts have little barbs that need to be clipped off with the snips.
  2. Try to size the Tee Nut to the diameter of the thermometer shaft you will be using. If it is not a really tight fit, don’t worry.
  3. Open the RTV sealant and, with and coat the inside (threads) of the Tee Nut . This will help the thermometer grip and fit snug. I use a small nail to coat the threads. The idea here is to be able to remove the thermometer, so don’t block the hole with the sealant.
  4. Drill a hole in the popper hood with a diameter a tad larger than the outside diameter of the Tee Nut shaft.
  5. Put 3 dabs of RTV sealant under the colar of the Tee Nut and fix it in place on the hood. Let it all dry before forcing the thermometer into place for the first time.