7 steps to hot rodding a Popcorn Pumper


This guide is intended for "educational purposes" only. 

I've tried this method, it works just fine, after 3 years of building them, I decided to invest in a 'real' coffee roaster ( a Hottop machine ) as I love the taste of fresh roasted coffee.


Messing around with electrical devices without proper training can, (at the very least)shocked. On the most dangerous level it might even kill you. If you don't know what you are doing, then find someone that you can trust to repair/replace and or modify all things electrical. 


People have been using hot air popcorn poppers for roasting coffee at home for years. Or so I've been led to believe by all the other  websites on the subject. 


If you can pop popcorn with a hot air popcorn popper, then you will be able to roast coffee, without too many problems!

The easiest & least expensive way to start roasting coffee at home is with a  West Bend Poppery 2 type hot air popcorn popper. 

The best 'out of the box' machine that I've found is the Proctor Silex Popcorn Pumper 1250 watt version. 

For less than $5. you can turn green coffee beans into tasty fresh roasted coffee beans. It takes about 15 minutes of your time to do a batch. A typical batch size in an un-modified machine is 3 oz. To roast up a pound of coffee, you are going to be there awhile. So, we learn how to tweak the roaster to properly roast a bigger batch.

Note: left clicking on the picture makes them larger, use your web browsers 'back' button to return to this page.

Here's how I did it:

Here is a Popcorn Pumper from my local Goodwill thrift Store.  $4.79

Step 1. You'll need a standard #2 Phillips cross tip screwdriver to begin. Remove this screw, under the front of the machine, first.

Step 2. Squeeze the electrical cord strain relief with a small set of vice grips. 

Use care when removing this piece and notice how it fits onto the cord. 

This is also a good time to examine the entire electrical cord for any breaks in the insulation, getting shocked is not much fun.

Step 3. Using a Flat tip screwdriver, very carefully insert and gently  apply a little pressure to lift the outer casing from the black plastic roasting chamber. It kind of snaps together & you just want to flex the cream colored outer shell.

Go easy here, using brute force WILL break the hard black plastic lock in tabs.

If you have made it this far, you are almost half-way finished!

 Step 4. Remove the heater and fan assembly, then separate them by removing 3 Phillips head screws.

Step 5. The bi-metallic thermostat. 

Removing the bi-metallic bubble allows the roaster to get a little hotter than the factory pre-set. Roasting coffee requires a little bit more heat, and 2 to 3 X more time than popping corn, & removing this piece allows that to happen.

Using a tiny 1/8th inch flat tip screwdriver, gently lift up on the bi-metallic contact enough to remove the shiny-bubble shape disc.  

Do not  try to bend it out of the way...just insert the blade & gently twist the screwdriver blade enough to lift the top contact & allow the disc to fall out. This is easier if you set it up on it's side & allow gravity to help you.

 Step 5a. If you over-bend the electrical contacts you will need to re-bend the metal to get those contacts touching. Otherwise, there will be no electricity, as you will have an open circuit. ( Not A Good Thing...)

Step 5b. The black bullet shaped thing with a gold band around it and has a wire seemingly going straight through it is the thermal fuse. 

I do not recommend that you bypass this in anyway, as it is protecting the popper from severely over-heating. 

You can test it with a volt meter to ensure continuity. 

If it's *open* or *blown*, then you can get a suitable replacement @ Radio Shack. A set of them costs less than $3. 

 Another view of the bi-metallic shiny bubble. After it falls out, you won't need it anymore.

Step 6. The slot widening portion is next.

This is best done from the 'outside' of the roasting chamber. The inside of the chamber is where you put your beans in, and they will swirl 'inside' of the roast chamber.

Think of making little hood scoops that will catch more air and force it into the roasting chamber. This is easily done as it's made from sheet-metal. 

Don't go crazy here, you only need to open them up a little bit.

If you try to do this without disassembling the popper, you will have a problem with smaller beans getting stuck in the slots. 

You are already inside the popper to 'fix' the electrical circuit to 'always on', you might as well improve the airflow, which also allows you to roast a larger volume, than you can in a stock popper. 

This step only takes a couple of minutes to do, and is really effective.


The above picture shows the correct angle to begin this process.

At the 10 o'clock position you'll see a good example of a 'widened' popper roasting chamber slot. 

Do this on all of the slots, and you are ready to re-assembe and test roast a batch of beans!

Another view showing that 'hood scoop' effect. 

Nothing dramatic, just run the small 1/8" flat tip screwdriver blade into the slot, give it a little twist. 

Form the scoop and keep doing it until all of the slots are evenly widened.

Step 7. Re-assemble the heater and fan assembly, and then put everything back together. 

The whole process takes about 10 minutes. Always check for any damage; broken wires on the heater elements, extension cord & any cracks in the plastic etc. 

 I like to use a permanent sharpie marker to write on the popper showing me the date of the modifications and what was done to it. Some of my poppers are 2 years old, & still working just fine.

After roasting a few test batches, I'll write down the temp and volume of the roast. Typically, you can roast around 5 + oz @ 55F, and around 4.5 oz @ 80F to get a nice, 10 to 12 minute Full City roast ( just before 2nd crack starts).

 A few snaps into 2nd crack and you will have a Full City + or FC++ roast level ( No oil present on the beans after roasting, but may be present 24 to 72 hours after resting.)

I like to use a glass chimney, and a 3/4" tilt with a piece of wood scrap molding. As you can tell, I don't think much about cleaning off the 'patina' finish. Seems to strengthen the glass ;-) 

I've probably roasted  over 300 #'s in that chimney. Use a pair of clean leather work gloves, dedicated for handling a hot chimney & use them only for roasting. 

I also have a pair of fire extinguishers nearby, just in case things go wrong.... 

Always unplug a popper after using it, and never leave the room while it's in operation. 

Things can go bad, quickly, and some people are easily distracted. Answering a phone call or leaving the room for 'just a minute' then forgetting about the roast... that's an invitation for disaster.

If you can locate a few good Pumpers, then you can rotate them on your roast night. Allow them to cool off for at least 30 minutes between roasts. I also use a regular tabletop fan to speed up the cool-down process. I'm sure this leads to a long and happy life for my roasters. 

 There are a number of how to roast coffee in a pop corn popper web pages out there , if you have any problems locating any great ones, then email me and I'll point you in the right direction.

I started here: Sweet Marias

Read up on a few things (bookmark them, & Just like Disney, you won't see everything in one day!)

Look for the Coffee Library... buy some green coffee beans, & proceed down the path...


 Garybt3@gmail.com or: Roasting Coffee at Home!