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Roasting Coffee At Home

Roasting coffee at home

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Home coffee roasters can be picked up for as little a £200/$315 and what some of them lack in control and stability they make up for in the fact that you have freshly roasted coffee on tap.

With a little trial and error these machines can produce surprisingly good results, and more expensive roasters can even match the quality of output that commercial models achieve.

Temperature control is everything in roasting. Most home roasters come with a panel that controls this digitally, and some have the function to programme a temperature curve so that the same roast can be repeated.

The controller for this is paired with a temperature probe that usually takes a reading from the metallic surface on the inside of the drum, or from the temperature of the air being blown in.

These temperatures are useful because they tell you how the roaster heats up, but this is only truly relevant when they're paired with a temperature reading from the beans themselves (bean mass).

Most roasters do not come fitted with a probe that can do this, so I suggest buying a digital temperature orobe and insertina it into the drum, or better still, connecting a USB probe to your computer or smartphone then using one of the excellent data logging apps that will record the progress of your roast.

Establishing a set-up like this is surprisingly cheap and easy, but provides a level of control and evaluation that will show in your coffee.

When you're choosing where to put your roaster ventilation is one of the main concerns. If you're roasting indoors I would recommend sitting the roaster underneath the extractor hood of your oven, or at least next to an open window.

Coffee roasting produces a lot of smoke, even on short roasts, and you'll not want it hanging around in your house.

Better still, do it outside or in an outbuilding, which solves the smoke problem and, for those of you that live in a colder part of the world, also helps a great deal with cooling the beans once they have been dropped into the cooling tray.

Follow the roaster's instructions and pay particular attention to the recommended batch size. Small home roasters can sometimes be very sensitive to small or large loads.

Under-loading leads to inconsistent cooking (like flash-frying, the bean may be underdeveloped on the inside) and overloading slows the roast down, which in extreme cases results in woody/smoky flavours.

Also locate where the chaff is collected and how it is emptied from the machine. If left to build up, chaff can cause problems with airflow and become a fire risk.

On a final note, it's important never to leave your roaster unattended - you'll not be able to enjoy the delicious fruits of your labour if your house burned down in the process.

Fire risk is something that commercial roasteries take very seriously, and roasting small batches in your home should be subject to the same degree of precaution.

  1. Preheat the roaster, it's important that the bean temperature ramps up quickly at the start of the roast, so sufficient preheating of the roaster's components is essential. Fire on all cylinders until the air temperature is at least 200oC/400°F.

  2. Drop the beans in and set the timer (A). The bean mass probe will show a sharp temperature drop as it comes into contact with the cool beans, but after around a minute it should bottom out and then begin to increase.

  3. Keep an eye on the bean mass temperature, which should be increasing rapidly, but beginning to slow its increase as you approach the eight-minute mark (B).

  4. First crack will present itself as an audible snapping noise after around 9-12 minutes, depending on the model of the roaster. It's here that careful temperature manipulation is required to stop the beans from 'running away' if too much temperature is applied, or from 'stalling' if your roaster has insufficient heat.

  5. As the beans develop after first crack the surface will become smoother and the aromas more pleasant. When you decide to finish the roast will depend on how you intend on brewing them as well as the type of coffee you are roasting. Experimenting with this is half of the fun of roasting.

    Having said that, if you'd like to stick to convention, most experts agree that first crack should occur at around 80 per cent of the total roast time. This means if you hit first crack at 10 minutes you should end the roast after 12 and a half minutes. You may of course wish to roast for longer. Drop the beans into the cooling tray (C)

  6. Some home roasters do a much better job of cooling roasted coffee than others. Ideally the beans should be cool enough to handle 5 minutes after the end of the roast (D). Bag them up and allow to outgas for at least 12 hours.

How to roast coffee perfectly