Coffee Roasting

Green coffee beans ready for roasting (and some roasted ones there too)

Green coffee beans ready for roasting (and some roasted ones there too)

Before I roasted coffee for the first time, I had never seen green beans before. They were smaller than I expected, heavier too, and they didn’t smell like coffee.

100g green beans is my default. More makes a faster roast, less prolongs it.

100g green beans is my default. More beans means a faster roast, less prolongs it.

The roaster I first used and still use to this day is a simple popcorn maker, which uses hot air to whirl the beans and roast them evenly, much like a commercial coffee roaster. The results are the same, only with a popcorn maker its only possible to roast 100g of beans at a time.

The popcorn machine and a steel bowl catching the chaff

The popcorn machine and a steel bowl catching the chaff

The first batch I ever roasted was perfect! I can still remember; they were Brazilian beans, roasted medium dark until their oils glistened over their surfaces. I had bought some professionally roasted Brazilian beans to compare them to. At three times the price, you can imagine the thrill of finding mine to be slightly better! Needless to say I was sold on home-roasting.

The next few weeks after the first roast saw me trying in vane to roast another batch exactly like the first. All my roasts were slightly sour, bitter or too burnt, and none of them roasted in the same time frame as the first.

Beans roasting medium. I usually keep them going until 'second crack'

Beans roasting medium. I usually keep them going until ‘second crack’. See the video here.

When green coffee beans are roasted, they go through phases of change affectionately known as ‘first crack’ and ‘second crack’. First crack is a loud cracking sound made by each bean as it expands in size and adjusts. At the right temperature, this should happen sometime around 4 minutes after the roast begins. Second crack sounds different; it’s when the outer shells of the beans are caramelizing and shattering – each bean crackles during this phase and this should be heard sometime around the 7 minute mark. The roast can be stopped any time after first crack – sooner will yield a light roast, and dark roasts are achieved during second crack.

There’s no temperature control on my popcorn maker, and with the same weight of beans as before, I was at the end of my tether before I remembered that during the first roast, I had a fan plugged into the same outlet. I recreated these conditions and found that the fan was drawing down slightly on the power going to the roaster, which made for a slower roast. Finally I could roast coffee (at least those Brazilian beans) reliably well each time.

I’ve since found that varying the amount of beans in the popcorn maker has an effect on the roasting time; less beans allows the hot air to leave the system quickly, slowing down the roast, whereas more beans traps hot air in and the beans roast quicker. Somewhere between 90g and 100g is where I’ve had best results. A different machine will need some experimenting to find the right ‘control’.

Two varieties of beans cooling before storage (and tasting!)

Two varieties of beans cooling before storage (and tasting!)

A good way to sample your roasted beans is to grab a couple – once they’re cooled – and eat em! Yes they should be bitter, yes they should be burnt, yes they should be sour, all of which might make this a horrible experience for you, but squint and focus on each of these tastes, as a good coffee is when all of these tastes are present but none obviously stronger than the others – eg if they’re more sour than burnt or bitter, chances are you didn’t roast them long enough, and of course too burnt means you let them go too long. On top of these major tastes, coffee has potentially hundreds of taste components for you to explore, but I’m not that sophisticated, so I’m just taking in the basics when I’m crunching down on them. Note also that you won’t get any additional flavours out of your coffee that aren’t already present in the beans that you’re crunching on – everything that’s possible should be present, and from here the coffee making process can only emphasise or destroy the flavours that are there.

Roasted beans are said to be good for about 13 days, after which too many of the volatile oils in the beans have gassed off and a really good coffee is no longer possible. Some people freeze their roasted beans to slow down this degradation, but it’s difficult to get away from the fact that the best coffee will come from freshly roasted beans, and its expensive to buy small batches of roasted beans every week or two. Green beans however, are said to be good for a year, stored in a dark cupboard in a cotton/breathable bag. Roasting green beans any time during this year will yield good results, so you can buy in bulk, roast a small amount each week or two, and enjoy the freshest coffee in town. And did I mention green beans are a 3rd the price of the same beans roasted?

See a video of how I roast coffee here.

Are you a coffee roaster?

What’s your secret?

What’s your favourite variety or blend and why?

Good things,


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