Fluid bed Vs Drum

[Andy]

Re: Fluid bed Vs Drum

Great post FC!
... of course all CSrs already "buy only the best visually well graded raw/green coffee"

From my own thoughts (NOT based on coffee experience but based on physics) an air roaster "could" roast more evenly.

My thoughts go something like this assuming that you can "suspend" the beans in air...

• Coffee gets lighter as it roasts.
• When you apply an equal force of air under the beans the light ones will go higher and roast less
• The heavier ones will sit closer to the heat source and get lighter
• You will always get a perfect roast.

Now the only "gotcha" I can see is that the above assumes the beans are all the same weight, shape and size and have the same aerodynamic qualities (ie: ping-pong ball round).

Hmm... maybe we need to base this on experience and not science

[Javaphile]

Re: Fluid bed Vs Drum

Theres also two types of fluid air bed roasters, those that recirculate the hot air and those that dont.

Java "Gotta love details" phile

[Fresh_Coffee]

Re: Fluid bed Vs Drum

Just some "minor" technicalities folks...

In commercial drum roasters, the hot air from from the burners is circulated through the drum itself before it goes up the chimney, This is done purposely, and the flow through of hot air contributes positively to the roasting process, also taking chaff & smoke away with it....

There are 2 common types of commercial drum roasters:

a) Those with a series of burners under the drum, that directly heat the drum, as well as then circulating the hot air through the drum, and
b) Those without any burners underneath...therefore no direct heat to the drum. These have a single high powered burner injecting directly into the drum from where it then recirculates around and out...

In terms of simple small home roasting drums, yeah ok the burners are usually underneath and there is no specific circulation of the hot air through the drum except by referred heat through the perforations in the drum...ofcourse some small drums have no perforations and are a completely "sealed" unit.

So not all drum roasters are the same.

Details, details, always so many details...

In terms of which is "better", fluid air bed or drum...in small home use fluid air bed machines, the coffee beans are usually  unevenly roasted. The operator needs to develop (by experience & patience) best practice techniques to suit both the individual roaster, and diff types of coffee, in order to minimise this unevenness. There is little if anything in the home use fluid air bed roaster itself that can be adjusted so the operator is left to fiddle realistically, only with time of roast, and quantity of beans.  Home use drum roasters on the other hand, probably as a result of their larger capacity in comparison to the commonly used fluid air bed roasters, and perhaps also as a result of the differing process where the operator is (theoretically) able to change the roasting parameters (drum revolutions & application of heat), are more likely to roast more evenly.

In either case, where very small quantities of coffee are actually being roasted in any particular batch at home, the result will always be far better if only really well graded (size & density)  samples are roasted. This will minimise uneven roasting.

So chaps, buy only the best visually well graded raw/green coffee!

Regardz,
FC.

[Javaphile]

Re: Fluid bed Vs Drum

Most Fluid Bed roasters are cleaned after every roast and so generally yield a cleaner, crisper tasting bean with each bean having just its own unique flavor. Drum roasters on the other hand are rarely cleaned and so tend to impart the build-up of flavors in them to every roast.

Java "Almost time for another roast" phile

[robusto]

Re: Fluid bed Vs Drum

Swig -- it would be nice to have a choice, but if youve got a popcorn popper, then youve got a fluid bed. If you have a rotating drum, the fluidity is the interval beans are bounced off the surface. If either is done right, I dont see problems with the respective methods. With fluid roasts the beans supposedly come into contact only with hot air, and because chaff and smoke is blown away, they dont become "contaminated" with their own by-products, producing a cleaner roast. With drums, some of the beans at some time are in contact with the hot surface of the metal drum -- at the expense of those deeper inside relying on the relatively cooler conductive heat. Thats why constant stirring is a must to produce even roasts. Stirring paddles or vanes and a reasonably faste rate of rotation will achieve that. With the fluid bed, the "stirring" is done by the hot air, but you have to keep batches fairly small to keep beans in suspension. Hope that helps...but in the end, as I say, your choice is made for you by the equipment you have or can get.

[swig]

Gday,

I am just starting out roasting, and would like to know if anyone has ideas on which is a "better" roasting process. Fluid bed of Drum roast?
Thanks