Roasting Coffee with a Popcorn Popper

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By Mark Prince

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Beyond getting my first fairly decent espresso machine (a Krups Novo Compact), my first real introduction into how good coffee could be has to be the day I discovered I could home roast with nothing more than green coffee, a hot air popcorn popper, and a metal colander.

I’m not talking a small jump here – I’m talking a quantum leap in discovering just how good coffee could be, and it wasn’t just in the taste improvements. Home roasting gave me for the first time a genuine insight into what goes into coffee.

I have the newsgroup alt.coffee to thank for this discovery. I remember reading about roasting at home as far back as 12 years ago in the newsgroup, and by 1997, I decided to take the leap. Probably the hardest part was finding green beans. I knew of exactly one local roaster at the time – a tiny place on West Broadway in Vancouver – where I might obtain green coffee. But their prices were prohibitive, so I wrote Barry Jarrett of alt.coffee fame (who runs Riley’s Coffee and Fudge in Illinois) and he sold me my first ever batch of green (months later, I was one of Tom Owen’s first dozen (or hundred) customers at Sweet Marias, long before he had his own domain name).

I read everything I could find online about roasting at home – and there wasn’t a helluva lot of information out there at that time. I heard about a book, called Home Coffee Roasting by some guy named Ken Davids, but I roasted my first batches before buying the book (highly recommended by the way).

Long story short, I started my amateur career as a home roaster, and all with a $20 investment, not including the coffee costs. It changed my perception of what coffee was, and along with milestones like getting a good grinder, was one of those huge leaps in terms of quality in the cup. By 2000, I was still roasting almost exclusively with a hot air popcorn popper, and I was building up my own “coffee cellar” of amazing coffees from around the world.

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No Warranty!
The moment you use a popper for coffee roasting, you void your warranty and absolve the manufacturer of any damage claims.

For a long time I resisted putting a popcorn popper home roasting how to on CoffeeGeek, for a variety of reasons. Truth is, I’m putting this online as a birthday present for my brother, Michael, who’s celebrating his bday on the day this is published. Long story 😉

This how to is designed to give you a bare bones introduction into starting your own home roasting hobby with little cost. For more advanced discussion, please join in on our popular Home Roasting Forum.

Please note: the following how to instructs you on using a product outside of its intended use, and one that will definitely void the warranty. It also presents some dangers – including the potential for starting a fire. If you choose to follow this how to, you do so completely at your own risk; CoffeeGeek.com is not responsible for any potential damage or harm using this method may cause, nor are we responsible for the products or the voiding of your warranty. In other words, use this how to at your own risk.

With that out of the way, let’s get into it!

The Tools you Need to Home Roast

The tools required for home roasting are those that won’t break the bank, even if you go all out. At the very minimum, you need the following:

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Popper Vents
Side vents are the best – they aid circulation of the coffee.

Hot Air Popcorn Popper. While there’s some debate on this, it’s preferable if you get a model that has side vents inside the machine, at the base of the interior funnel. Some models have a grate on the bottom, and are generally not recommended.

Mesh colander One big one should suit, but two are better. You need these to cool down your beans as quick as possible – tossing the sizzling hot beans from one to the other is how you do it. Alternatively, you can use an extra large cookie baking sheet – the large surface area will quickly “leech” away excess heat from the beans.

Large Bowl: really, any bowl will do; but it has to be big. You place the bowl in front of the popcorn popper’s air chute to collect all the chaff that will blow off your coffee as it is roasting.

Oven Mitts: to handle the hot popper as soon as you unplug it and want to remove the top and dump the beans out into your colander or cookie sheet.

Green Coffee:These days, there’s dozens of sources online for amazing quality green coffee. Some even advertise on CoffeeGeek (more really should, though ;)). I’ll leave you to visit the Forums to find recommendations.

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The Popper
Any hot air popper will do – this is a $17 model from London Drugs in Vancouver.

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Colander
This is an oversized colander from Ikea – enough to sift up to a few 100 grams of coffee.

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Chaff Bowl
A huge bowl – steel’s not necessary – to collect chaff.

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Oven Mitts
Any will do – these are the silicone style mitts that have recently come on market.

What you need to know

I can’t stress enough that this how to is a “do at your own risk” type instructional. Using a popcorn popper to roast coffee definitely voids the product’s warranty. Also, most current-day popper will burn out within 4-6 months of roasting coffee, because of the maximum stresses put on the machines – way beyond what they normally do for popcorn.

Home roasting is also extremely hands on. You must never leave the popcorn popper while it is roasting coffee. At temperatures as high as 475F, things can spontaneously combust and catch fire. It rarely happens, so you shouldn’t worry too much about this, and I’ve never heard of anyone setting their kitchen on fire while actually paying attention to the roasting process. Fires have happened, but in almost every case I’ve read about, it was through negligence – the home roaster left their appliance alone, and the coffee was roasted beyond a dark roast, and eventually ignited. While the danger is almost non-existent if you’re hands on, having a fire extinguisher or bucket of water nearby, or roasting out doors is definitely recommended. IF you do see a fire start inside the popper, unplug it and douse it with the fire extinguisher or water.

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Coffee Chaff
This stuff is going to get everywhere. If you roast outside and it’s windy, don’t even bother with the bowl.

Oh and chaff. It’s going to get everywhere! 🙂

With the scary stuff out of the way, you also need to know the following:

  • Roasting in a popcorn popper typically takes about 5-7 minutes for a light roast, 7-8 minutes for a darker roast.
  • Most popcorn poppers on the market today roast about 75-85 grams of green coffee per batch – or enough coffee for a 10 cup pot. You can usually do 2 or 3 back to back roasts, but this will shorten the popper’s life.
  • Your ears and eyes and nose will tell you how your roast is progressing. It’s not something that we can really fully train you on in this how to – it comes with experience. You’ll soon be able to distinguish between first and second crack (explained below), and the different smells during the roast.
  • Even with the dire warnings above, home roasting is very safe – I’ve roasted at least 1,000 or more batches in popcorn poppers over the last 10 years, and have never had anything beyond a slowly melting plastic lid.
  • Coffee loses up to 20% of its weight during roasting (and also increases in physical size by about 30-40%). So 85 grams of green can deliver as little as 70 or less grams roasted.
  • Coffee needs to rest 2-5 days after roasting, as it degases. But you’re welcome to try the coffee right after roasting, a day after, and two days after, if for no other reason to discover how coffee matures, peaks, and then declines after its roast date.
  • And one more caveat – I’ve read that the some recent models of popcorn poppers now have a heater cutoff fuse that will shut down the heating coils once the temperatures get above 400F. I’ve not experienced this myself, but if you buy a popcorn popper and it can’t seem to roast past first crack, this may be the reason why. Caveat emptor.

Step by step

Are you ready? Here’s the visuals and step by step instructions

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85 grams
85 grams is a good starting point for most popcorn poppers. You’re saving a ton by home roasting – splurge on good quality beans. These are Honduran CoE coffee samples.

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Pouring the Beans
Plug your popper in and let it warm up for maybe 30 seconds. Quickly pour in about half a cup of coffee, but here’s a quick and dirty way to tell how much coffee your popper is capable of roasting – pour in enough green quickly until it just barely is rotating in the machine – just barely. That’s your max amount. If you want, unplug the popper and weigh the coffee to know your ballpark weight

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Stirring early on
Grab a wooden spoon or similar, and stir the coffee right away. Note that we’ve kept the lid off for the beginning part of the roast. Adding the lid soon will help retain heat in the popper, so once the beans start rotating a bit more, the lid goes on.
Bean colour: Still green, starting to tan.
Smell: barely there sweet barley

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Chaff Collecting
Once you start seeing chaff (the coffee’s silverskin) coming out of the chute, things are starting to really happen with the coffee. This is about 2.5 minutes in.
Bean colour: medium-dark tan, “cinnamon”
Smell: sweet barley

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First Crack
About 4 minutes in, you’ll start to hear a sound that sounds like a gentle fire crackling away. This is known as “first crack”, or when the internal cell walls of the coffee bean are being fractured by heat and boiling oils. At this point, coffee is entering the light roast or “city roast” style. Depending on the coffee, the roast can be stopped at any time after first crack begins.
Bean colour: light-medium brown
Smell: oils cooking, muted

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Temperatures
If you use the optional thermometer mod (mentioned below), the coffee should be about 420F once first crack has really starting going on. Eventually it will subside.

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Second Crack
About 5 or 6 minutes in, and after a pause in hearing the first crack ending, you’ll start to hear a different kind of crack, more muted but a higher pitch than the way first crack sounded. It will also increase in frequency, constantly. This is called “second crack” and it happens when the surface walls of the beans are fractured by what is now tiny little furnaces inside the bean. At the moment second crack starts, the beans are a “medium roast” or “Full City” style roast. Again, you have the option of stopping the roast, or continuing at this point. Surface oils will start to show up soon.
Bean colour: medium-dark brown
Smell: burning oil, burning organics (not wood)

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Dumping the Beans
You can take the roast darker, but I typically like to try every bean I roast at “Full City +” or about 30 seconds into the start of second crack. Once it’s at the level you want (you can peek by removing the plastic top of the popper briefly as it roasts, but use your mitts and be careful), unplug the popper, and quickly dump the coffee into your colander or cookie sheet. **Be Careful!!** The coffee is about 450F or higher at the end of the roast!

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Sifting the Beans
If you have one colander, go outside quickly and start sifting the coffee to aerate it and also rub off additional chaff (it flies everywhere). If you have two colanders, quickly pour the coffee back and forth between the two of them. If you use a cookie sheet, just slide the coffee around – the sheet will get really hot but that’s a sign of it acting as an efficient heat sink for the roast.

Optional Tools

The above is really all you need to roast coffee at home; that said, here’s some optional choices to make the roasting job more educational, less seasonal, and more consistent.

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Digital Scale: Popcorn poppers typically roast about 75-85 grams of green coffee – roughly enough to produce a 10 cup pot of coffee – though some can roast more, others roast less. A digital scale helps you be more accurate in not only doing consistent roasts, but also finding out what the ideal green bean starting weight you need is.

Candy Thermometer: Most of the needle thermometers you see out there are designed for baking and meats, and measure up to around 220, 250F, but there is a special type of needle thermometer that can measure up to 550F or higher (but costs about the same as the other meat thermometers – around $10-$15). You need the higher temperature one to measure your roasts, which can get as high as 475F.

You can use the thermometer in several different ways. Many people literally drill an angled hole in the side of their poppers so that the needle sits right in the middle of the rotating coffee, and can easily be read while the roast goes on. You can also drill a hole in the plastic lid of the popper, but I’ve found the thermometer gets so hot there, it slowly melts the plastic, deforming it.

Use the thermometer to chart things like at what temperatures 1rst and second crack occur, when you want to stop the roast, etc etc.

Modding your popcorn popper roaster

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Candy Thermometer
Called a “candy” therm because of the higher temperature readings (meat rarely needs to be read to 550F). Easy to find in any kitchen store

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Drill Time
Unplug the popper, and determine the best angle you should drill your holes through it so the needle isn’t sitting on the bottom. Eyeball it or measure, then drill. You’re going through plastic then metal.

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Therm in place.
In place, it’s easy to see and read.

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Fully inserted
While not optimal (that would be dead centre, about half an inch above the bottom), this is pretty good – the needle sits above the bottom by about 5mm, and should give good readings.

Big Brown Box: If you want to roast outdoors and live in a colder climate, get a box big enough to fit both the popper and your big bowl for the chaff in. Even in temperatures as low as 0 Celsius, the box acts enough as an insulator to keep the area around the popper warm so it doesn’t screw up your roasting times. Poppers do not like cold weather. Just don’t burn everything down 😉

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