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  1. #1
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    Fluid Bed vs Drum Roaster: Exact same results?

    With the right air temperature control system, will a fluid bed roaster perform the same as a drum roaster like a Probate? If the beans in a fluid bed roaster go through the exact same temperature changes as in a drum roaster, wouldn't the results be exactly the same for both approaches?

  2. #2
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    It has something to do with how that heat is transferred to the beans, and that's why the two produce different results. It's not just what temp the beans are at, but how the came to be at that temp.

    That said, a very good friend, is the owner of https://www.ihaveabean.com/ who designed his own FAB roaster, and it does a great job. He was a software designer before starting the coffee business and wrote code to control the electric heater and blower that lofts the beans, so his profile can be adjusted in minute detail and repeated perfectly. Pete puts out some great coffees.

  3. #3
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    That's interesting because I'm also an engineer. I've taken the Probate roast profiles published at cafeimports dot com and matched them exactly in my fluid bed machine. Same bean temp at the exact same time. I think the results are pretty good. The big difference that I see in what I'm doing is that beans go into the roaster with it off, and the temp is bought up to the initial drying temperature. They can never burn because the air temp starts out low.

  4. #4
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    I have participated in blind cuppings comparing both types of roasting machines--same coffees, same profiles as much as can be duplicated--and the drums were chosen as best 90% of the time.

  5. #5
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    Quote Originally Posted by thCapn View Post
    I have participated in blind cuppings comparing both types of roasting machines--same coffees, same profiles as much as can be duplicated--and the drums were chosen as best 90% of the time.
    That's is very interesting. Would you be up for a small friendly challenge. I'm thinking if you can send 4 oz of drum roasted beans, plus 5 oz of green beans. I'll roast the green beans to the same profile, number the two batches and send them both back to you for blind taste testings. It would be best to have several people involved as the would be a 50% chance of getting it right. If you thought this was a good idea and had several folks involved with the tasting we might have to go to 8 oz. Like I said, I can track the exact temp profile of a drum roaster. If you are correct, and I have no reason to doubt you, then we would have to reconsider the direction we go in as far as roasting technology.

  6. #6
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    Quote Originally Posted by boreland View Post
    With the right air temperature control system, will a fluid bed roaster perform the same as a drum roaster like a Probate? If the beans in a fluid bed roaster go through the exact same temperature changes as in a drum roaster, wouldn't the results be exactly the same for both approaches?
    I will differ with the others. Fluid bed coffees are brighter and have less body than coffee from a drum roaster. Why the difference, even if temps were the same? One is having its development from air, the other conducted from metal and air.

    I will also add, this is opinion, as are others' views. It comes down to taste and preference, though when debates occur, sides often treat their view as fact.

  7. #7
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    I would be open to trying something like that. However, I do not have the means to roast in such small batch sizes.

    Anybody else?

  8. #8
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    Fluid Bed = Convection
    Drum = Convection and Conduction, with convection being ~65% of the roasting activity

    I don't know this for a fact, but I also suspect that the design of the drum interior and how it tumbles the coffee helps to create some of the differences.

    But after all of that, it's really down to what our customers like best and what they will pay their money for. Creating critically acclaimed and award-winning coffees may be good for one's resume and reputation, and can lead to opportunities to make money, but they don't pay the rent in and of themselves.

  9. #9
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    The differences come down to the way the coffee is mixed within the roaster - mixing is required to ensure the beans are roasted evenly within a batch. On a Fluid Bed Roaster, the mixing is achieved through the airflow which has to be maintained at a sufficiently high velocity to move the coffee around. For a Drum Roaster, the mixing is achieved by a mechanical agitator (the rotating drum). Consequently, the airflow on a Drum Roaster can be much lower.
    The heat transfer to the coffee beans on most roasters is a combination of convection (from hot air) and conduction (primarily from bean to bean). There is some radiant from hot metal, but it is minimal. There is also some conduction from the hot metal, but it is minimal too. As thCapn described, the vast majority is through convection. With the higher airflow on a Fluid Bed Roaster, the boundary layer around the bean is reduced which creates the potential for more heat to be transferred. However, some argue it also is likely to remove more of the gases that were within the bean's boundary layer and create a different roasted coffee. Lowering the airflow on a Fluid Bed Roaster is not an option since the mixing operation is still required.
    Typically, for different roasters roasting the same coffee, the same batch size, over the same 'roast profile' (i.e. time/temperature curve), the Fluid Bed Roaster will have a lower inlet air temperature to compensate for the higher airflow. But it is unlikely to cup the same as a Drum Roaster due to the fundamental differences in the way the heat is transferred. Now this is not saying the coffee from one roaster is better, just different.

  10. #10
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    Quote Originally Posted by BoldJava View Post
    I will differ with the others. Fluid bed coffees are brighter and have less body than coffee from a drum roaster. Why the difference, even if temps were the same? One is having its development from air, the other conducted from metal and air.

    I will also add, this is opinion, as are others' views. It comes down to taste and preference, though when debates occur, sides often treat their view as fact.
    In the industry, that translates to flatness and under-developed roast. I have roasted on a Sivetz (a fluid bed roaster) for years and always had an affinity toward coffee roasted via air. It wasn't until I left my previous employer and was able to snap out of the transe. After extensively cupping coffees roasted on a fluid bed roaster against the same coffee roasted on a drum roaster, the difference comes out. The coffee roasted on the fluid bed roaster is constantly punished on cupping tables in body, acidity, and finish. They often have descriptors like baked, flat, and under-developed placed beside them. Roasting these coffees to SCAA standards for cupping, the type of roaster used can easily be responsible for giving a perfectly good coffee weaknesses where they wouldn't otherwise exist.

    If fluid bed technology was superior, reputable manufacturers such as Probat (not Probate), Diedrich, and Giesen would jump on the bandwagon. The reality is they havent. The companies stuck with making fluid bed roasters like Sonofresco, Java Masters, Ashe, and Coffee Crafters are the laughing stock of the industry -- and for a good reason!

 

 
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