oldgearhead Senior Member Joined: 25 Jan 2010 Posts: 397 Location: Go Colts! Expertise: I like coffee
Grinder: Virtuoso by Baratza Drip: Chemex,Dilongi DCM900 Roaster: 1/2K Fluid-bed
Posted Tue Nov 12, 2013, 5:44am Subject: Re: Fluid bed vs Drum--why different curves?
Of course another 'feature' of a fluid-bed roaster is you can adjust the roast by either the air-temperature control, the air-flow control, or both. I started out with my fluid-bed roaster by adjusting the flow control twice, at 3 minutes and 6 minutes, also I set the air temperature three times: 470°F, 650°F, and 580°F (drying, ramp-to-first-crack, and finish). Recently, however, I've been setting the temperature based on the density and test weight of the bean being roasted and adjust only the air-flow during the roast. Example (SHG bean): I set the air-temperature at 550°F, turn the air-flow down at T+ 3 min., again at T+ 6 min. and turn it up at T+9 min. The roast Bean Mass Temperature (BMT) responds much quicker to air-flow changes than to heating-element current changes in my heat-reclaiming, electric, 120V, one-pound, fluid-bed roaster. In general the curve I'm using now is very similar to the one I started with:
July 2011 __T+0 = Drying, 4 min. (470°F) __T+4 = Ramp-to-first-crack, 4 min. (650°f) __T+8 = Finish, 3-4 min. (580°F)
July 2013 Air-temperature = 550°F Adjust air-flow only _T+0 = Start Drying _T+3 = turn down to 'creep' _T+6 = turn down to 'creep' _T+ first crack = turn up
However, the drip coffee is a bit more full-bodied, and sweeter. It seems that I get a much more complex cup when I use lower air temperature to move first crack from T+8 minutes to T+ 9.5 minutes. ___________________________________________________
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