Modifying a popper for controllable coffee roasting: Pt 1
Modifying a UK Prima Popper for controllable coffee roasting, by 'mnemonix'
This is the most commonly available Popcorn machine in the UK, the Prima PCM001, which also comes as a 'stainless steel' version though this is identical other than having a sheet of aluminium wrapped around the plastic body. Note, it does not look like a duck. Do not buy one resembling a duck or any other animal. It's not natural (and they're only rated at 600 Watts).
One thing before we start. If you are lucky, your popper is eventually going to start melting. Unlucky, and you'll be setting things on fire. They just aren't designed to run as long and hot as it takes to roast coffee but that said, they do a very good job of it, cost very little and to date, only the hood of my first popper has suffered slightly from Dali Clock Syndrome. You must never leave a popper unattended whilst roasting however.
With the UK mains of 240V as opposed to 120V in the States we do not have the problem of insufficient power, and the popper in its standard form tends to roast far too quickly, reaching 2nd crack within 3 minutes or so, which can lead to uneven roasts and does not allow for the full development of flavour in the roast coffee, which I found both muted and slightly sour despite my initial joy at the first successful roast.
To overcome this one can switch the popper off periodically while
stirring the beans manually to prevent them burning against the hot metal
of the chamber and I have successfully stretched my roasts over 10 minutes
in this manner usually following a pattern of continuously on for the
first 30-60 seconds followed by equal periods on and off of about 10-15
seconds each. Later in the roast and using a thermometer as a guide I do
it more by feel to nurse the roast through first crack and up to second.
The best results are obtained by turning the popper on and off more
frequently and therefore for shorter periods of time to prevent the roast
stalling, however doing this more frequently than every 10 seconds or so
becomes impractical not to mention faintly comical to watch given the
frantic stirring, hence the interest in modifying the popper for more
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