Roasting your own coffee at home

Easy home coffee roasting, better, cheaper coffee for minimal effort.


Low, possibly negative as green beans are much cheaper than roasted.


Low. Pour in, turn on, pay attention, pour out, shake, wait three days.


Had an opportunity to pick up some reasonably priced green coffee beans during lockdown.

So decided I’d get back into roasting my own. Conveniently had picked up an old popcorn machine shortly before lockdown.

Home roasting is super easy with a popcorn maker and the length and breadth of different options you can create is endless.

There’s something like 30+ different recognised coffee bean origins and types, 5 different roast methods, plus blending. When you go to the supermarket, you usually have a choice of like 3 whole bean options all with the same dark roast.

Absolutely the way to go with a minimal amount of effort. And many people have a popcorn maker lying around the house they used once and put away.


  • Green Coffee Beans, Google it, plenty of sources who will ship. Cheapest I’ve bought were $9/KG for Indian Robusta. I’ll add a comment saying where I bought mine from as this article isn’t an ad. Maybe I’ll write another article another day on picking beans.
  • Popcorn maker (See below)
  • Bowl
  • A metal tray (or large pot)
  • A sealable container (jar, or Sistema plastic lunchbox)
  • Optional: A fan

Choosing the Popcorn Maker

I’ve now experimented with three different popcorn machines over the years, and found one to be the best (of which I’ve tried) but have learnt a few things from each.

What I’ve learned so far, is there’s two major things to look out for:

The louvred bottom:

This is where the heating chamber has louvred vents around the bottom which causes the air to flow through in a circular pattern. The alternative to this is a mesh or holes on the very bottom.

The louvres at the bottom (the directional vents) are a must, this is the Sunbeam Cornelius

This circular motion ensures that all of the beans are moving at the same speed and regularly getting mixed up, so that they’re evenly heated and roast at the same rate. As popcorn finds its way out of the chamber when hot enough without emitting oils, evenly heating corn kernels isn’t as important, and so the mesh versions are fine for popcorn, but they don’t evenly move the coffee around, and can cause uneven roasting.

Additionally it ensures that any oils emitted by the beans don’t collect and eventually find their way onto the heating element. Which could be a potential fire risk.

The louvred bottoms are a must have on your popcorn maker.

A long chamber:

This is harder to spot before buying, so is more just a trial and error thing. My most recent popcorn maker taught me the importance of this.

Basically as the beans roast, they expand and lose density. This causes them to accelerate as the roast goes on and for them to reach higher and higher up the chamber. If they get high enough, they can jump out of the machine and you’re constantly fighting a battle to keep them in, with them cooling slightly every time you put it back in.

This paragraph is theory, but I was fighting with a machine with a short chamber and just couldn’t get to second crack. I theorise that a longer chamber increases the overall chamber temperature, possibly as the heat is kept in contact with metal for longer. I eventually gave up after the casing at the top started melting and settled on a medium roast after a roast period easily twice as long as the other models.

The three machines I’ve now tried were:

  • a random old model at the op shop that I found. Unfortunately I can’t remember enough about it to be helpful, aside from it giving a good roast. Looked like the white one in the picture.
  • A Sunbeam Cornelius, a model that was so good, that I bought a second and am using it as my basis for building a fully automatic coffee roaster. Sunbeam has a new model, which looks equally good, but it remains untested.
  • A Sheffield Novelty Popcorn maker. Terrible, and by far the most expensive consumer model I could find. Short chamber, I couldn’t get better than a medium roast after a period almost twice as long. The casing started melting and I was constantly putting the half roasted beans back in.

New or Used:

Used, absolutely. The market is flooded with popcorn makers people have bought once and put away, never to be used again. They’re an otherwise mostly useless appliance. I haven’t paid more than $10.50 for a popcorn maker so far. That Sheffield one I bought was $10.50 on TradeMe, but $149 at Farmers.

Don’t buy a new one unless you’re desperate.


Warning: Coffee roasting smells awful. Smell is a big part of the roasting process, you learn to pick up different acidity levels during the roast to get your ideal, so for the roaster you don’t think it smells terrible, but it does. And it easily fills up the entire house. At a bare minimum, do it in front of an open window, but ideally outside, in the garage or something. Roasted coffee smells amazing. Roasting coffee smells terrible.

Now that the warning is over, the actual roasting part is quite quick, I’d estimate about 5 minutes or so of just standing around listening and smelling.

The popcorn maker roasts the beans, the metal tray/pot and fan are for cooling down the beans after roasting. And the jar to store them. If you have a fan, plug it in and have it somewhere convenient, like on the bench. And have the pot/tray at arms reach.

Start by adding your beans to the chamber. I’ve always eyeballed it, but about this much, which is what…three quarters of a cup? If you have a short chamber, you’ll have to add fewer beans. This amount will make maybe 8-10 cups of coffee. You’re better off trial and erroring your way through bean quantities, as it can also depend on how much coffee you drink and your popcorn maker.

On the Sunbeam Cornelius there’s a line above the louvres, which is coincidentally about the same level that I roast.

Put a bowl in front of the machine to catch any chaff, which is the skin separating as the bean expands, put the lid on and hit the power switch.

Now just wait, the beans will slowly start spinning and progressively increase in speed. There’s not much you need to do for the first few minutes.

After around, maybe two minutes, the beans should have a decent pace to them and you should start hearing what is called “First Crack”, which is very mild popping/cracking sounds of irregular frequency. As the beans heat up, they expand and that noise is them breaking apart internally.

Remember the noise, as one popular roast type, the “City Roast” occurs right after “Second Crack” followed by all of the dark roasts.

It’s around here that you want to pay attention to the sights, sounds and smells, as the acidic roasting aroma should be kicking into high gear around now. It will take a few roasts but you’ll slowly learn to distinguish between the different aromas. For the first few, you can just rely on theory, stop it as “Second Crack” starts to disappear and you can physically see it get dark for a good starter “City Roast”.

I’ll add videos to this article soon, I have to boost my upload limits on my server. But one of the videos is of second crack occurring, so you can get idea of what to listen for.

Once you decide that the beans are roasted to the correct degree (I’ll add some detail at the end about the different roasts), turn the machine off and pour them straight onto your tray/pot.

The goal is to cool them down as quickly as possible, as they’ll continue to roast and darken further on their own.

My method to do so, is to roll them over metal in front of a fan, but you can also do so outside in a wind. The air pulls the heat away from the metal, and the metal pulls the bean from the beans.

Via this method, I find they’re cool enough to touch within maybe 40-60 seconds.

Once you can handle them, well, that’s it. You’re done. Put them in the container with a loose lid to let them “degas” for at least 1 day, but ideally 3. Then tighten the lid.

At this point they’re releasing a lot of CO2 and their flavours won’t be at their best until around day 3, and they’ll stay at their best up to around day 7. So you’d aim for a quick roast every three days or so.


  • Put Green Beans in Popcorn Machine
  • Turn on, wait for second crack
  • Turn off, cool them down as soon as possible
  • Store for 3 days

Table of Roast Types

22 °C (72 °F), Green BeansGreen coffee as it arrives at the dock. The beans can be stored for approximately 12–18 months in a climate controlled environment before quality loss is noticeable.
165 °C (329 °F), Drying PhaseDuring the drying phase the beans are undergoing an endothermic process until their moisture content is evaporated, noted as the yellowing phase.
Light Roast
196 °C (385 °F), Cinnamon RoastA very light roast level which is immediately at first crack. Sweetness is underdeveloped, with prominent toasted grain, grassy flavors, and sharp acidity prominent.
205 °C (401 °F), New England RoastModerate light brown, but still mottled in appearance. A preferred roast for some specialty roasters, highlights origin characteristics as well as complex acidity.
Medium Roast
210 °C (410 °F), American RoastMedium light brown, developed during first crack. Acidity is slightly muted, but origin character is still preserved.
219 °C (426 °F), City RoastMedium brown, common for most specialty coffee. Good for tasting origin character, although roast character is noticeable.
Dark Roast
225 °C (437 °F), Full City RoastMedium-dark brown with dry to tiny droplets or faint patches of oil, roast character is prominent. At the beginning of second crack, body is fully developed.
230 °C (446 °F), Vienna RoastModerate dark brown with light surface oil, more bittersweet, caramel flavor, acidity muted. In the middle of second crack. Any origin characteristics have become eclipsed by roast at this level.
240 °C (464 °F), French RoastDark brown, shiny with oil, deep caramel undertones, acidity diminished. At the end of second crack. Roast character is dominant, little of the inherent aroma or flavors of the coffee remain.
245 °C (473 °F), Italian RoastNearly black and shiny, burnt tones become more distinct, acidity nearly eliminated, thin body.
Source: Wikipedia

Future Plans

I’m in the process of building an automatic coffee roaster, where you select your roast and it does the whole roast process for you, with sensors to detect each level. So I’ll write an article (or several) about that soon.

One thought on “Roasting your own coffee at home

  1. Most recently I’ve been buying green coffee beans from these guys, and they keep sending me coupon codes via email. So if you’re interested, ask me and I’ll post any current codes. However I’d still suggest Googling and finding your own ideal supplier. I just bought from these guys once because the coupon made their beans cheap.

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