What does coffee taste like when you use too much airflow? - Page 2

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
popeye
Posts: 340
Joined: 18 years ago

#11: Post by popeye »

In my opinion, airflow is one of the least explored variables when it comes to coffee roasting. Temperature has come to be synonymous with heat (really heat transfer) but heat transfer seems to be a complex function with multiple variables (of which airflow is one, and roaster design contributes a good bit too).

Airflow and temperature delta (ET-BT) have an inverse relationship for a constant heat transfer. You can roast with increased airflow at a lower temp delta for the same heat transfer.

The only specifics I've observed so far (and this is sketchy observation that works for me on my roaster) is that too little airflow after first crack results in an ashy overtone that sits on top of the coffee. For this reason, i limit my diedrich to no less than 27 degrees on the damper after first crack. It's easy to try to reduce heat (and airflow to keep ET from dropping) too much after first crack. The roast won't stall (8+ degrees/min ROR) but the airflow has to come way down to maintain ET and then boom ashy overtones.

Writing this right now, i'm guessing a possible cause is that as the airflow goes down too much, the heat transfer ratio between the drum and the airflow shifts too much toward the drum. This is actually pretty possible on my diedrich because the airflow enters the drum by first flowing around the outside of it. With low airflow, it's possible the drum actually overheats. I currently don't have instrumentation directly reading the drum temp, but i can get at it with an infrared thermometer if I dissemble part of the roaster. Maybe i'll do so.

Anyway, as i said, airflow is a little explored variable and it's probably pretty specific to your roaster. A drum roaster with a different design than a diedrich might not even have the issue I do.
Spencer Weber

HoldTheOnions
Posts: 764
Joined: 9 years ago

#12: Post by HoldTheOnions »

Mile High Roaster wrote:Consider this excerpt from the following paper- I think he is onto something: http://e-collection.library.ethz.ch/view/eth:23461

"The amount of hot air in relation to the coffee batch size turned out
to be critical for roaster design and operation. Low air-to-bean ratios resulted in
coffee of superior cup-quality, whereas excessive air streams led to products of
bland, dull and flat sensory properties. A lower ratio is assumed to prevent physical
aroma stripping and excessive contact with oxygen and may create a favorable
"microclimate" enclosing the beans. These findings also stress the important role of
oxidation processes during roasting and storage."
Thanks for the link, it's interesting. I previously controlled temps primarily through heating element, but I have shifted to controlling temps by lowering fan speed during the roasts and keeping heating element the same. This is primarily because it is easier to control temps through fan speed than heating element and because higher fan speeds in the beginning of the roast give a far more even roast, which has very noticeable benefits in the cup IMO. Overall my results have dramatically improved, which is to say I haven't noted that higher fan speeds negatively impact the roast, in fact it seems exactly the opposite. But it could be my roasts improved due to better ramping technique during the phases, but they are still deficient compared to if I were to keep fan speeds as low as possible and ramp primarily through heating element.

Other thing is I turn the fan down during the roast and by development time it is churning pretty slow. So wondering the effect of fan speed during different phases of the roast. Maybe higher fan in the beginning is ok or far less bad?

Regardless, this has given me a new idea to try. Previously, I tried keeping fan speeds as low as possible during the entire roast without good results, but now thinking I will try to keep it higher during drying phase for evenness sake, and then from that point more aggressively lower fan speeds and adjust heating element to keep the roast on the same track. Maybe can make it better.

HoldTheOnions
Posts: 764
Joined: 9 years ago

#13: Post by HoldTheOnions »

popeye wrote:Anyway, as i said, airflow is a little explored variable and it's probably pretty specific to your roaster.
It seems like they explored it pretty good in that paper ;-). Kidding aside, you make good points, and what is sticking in my craw is whether they have covered all the bases. I would test this concept by generating the same bean temp curve using different air speeds and then comparing results. I keep going back and forth on whether their procedure is constructively the same or not, I am not convinced it is.

User avatar
NoStream
Posts: 283
Joined: 10 years ago

#14: Post by NoStream »

Mile High Roaster wrote:Consider this excerpt from the following paper- I think he is onto something: http://e-collection.library.ethz.ch/view/eth:23461

"The amount of hot air in relation to the coffee batch size turned out
to be critical for roaster design and operation. Low air-to-bean ratios resulted in
coffee of superior cup-quality, whereas excessive air streams led to products of
bland, dull and flat sensory properties. A lower ratio is assumed to prevent physical
aroma stripping and excessive contact with oxygen and may create a favorable
"microclimate" enclosing the beans. These findings also stress the important role of
oxidation processes during roasting and storage."
I'm reading through the paper now. I really don't think you can generalize. As already has been pointed out, they're using a fluid-bed roasters. Perhaps more importantly, their high-temperature short-time procedure is absurdly hot and fast - far closer to industrial processes than more aggressively fast artisanal / third-wave ones.

User avatar
TomC
Team HB
Posts: 10535
Joined: 13 years ago

#15: Post by TomC replying to NoStream »


This whole article cited is based on industrial roasting, not artisanal. It's like comparing apples to walnuts.
Join us and support Artisan Roasting Software=https://artisan-scope.org/donate/

popeye
Posts: 340
Joined: 18 years ago

#16: Post by popeye »

TomC wrote:This whole article cited is based on industrial roasting, not artisanal. It's like comparing apples to walnuts.
As evidenced by this line from the paper:

"Sensory evaluation by an expert panel: A quantity of 12g ground roast coffee was placed in a porcelain drinking bowl,and 0.3 L boiling water was poured over it. The coffee suspension was stirred and allowed to cool down to approximately 50 °C, while coffee particles deposited. Three expert coffee tasters sipped the beverage using spoons."

Nevertheless, I am impressed they got actual thermocouples mounted inside of individual beans. I will have to finish reading the paper sometime.
Spencer Weber

User avatar
NoStream
Posts: 283
Joined: 10 years ago

#17: Post by NoStream »

popeye wrote:water was poured over it. The coffee suspension was stirred and allowed to cool down to approximately 50 °C, while coffee particles deposited. Three expert coffee tasters sipped the beverage using spoons."

Nevertheless, I am impressed they got actual thermocouples mounted inside of individual beans. I will have to finish reading the paper sometime.
I'm reading through it and actually finding it useful. You just need to remember that a lot of the findings don't generalize.


More on topic, from a Tim Wendelboe talk, he says that coffee ends up "stripped of aromas if airflow's too high." For reference, he's working on a 15 kilo Probat with a modified fan system that gives him quite a bit of control and headroom. (See - http://www.coffeeawesome.net/february-2 ... oe-part-2/ )

User avatar
TomC
Team HB
Posts: 10535
Joined: 13 years ago

#18: Post by TomC »

popeye wrote:
Sensory evaluation by an expert panel: A quantity of 12g ground roast coffee was placed in a porcelain drinking bowl,and 0.3 L boiling water was poured over it. The coffee suspension was stirred and allowed to cool down to approximately 50 °C, while coffee particles deposited. Three expert coffee tasters sipped the beverage .

I wonder how great that tasted :|
Join us and support Artisan Roasting Software=https://artisan-scope.org/donate/

HoldTheOnions
Posts: 764
Joined: 9 years ago

#19: Post by HoldTheOnions »

I did a couple yesterday, one using my pro-typical air ramping and the other using a low air style. I brought to the same point and couldn't tell them apart by looking at them, so in a couple days we will have a conclusive answer. :shock:


:lol:

HoldTheOnions
Posts: 764
Joined: 9 years ago

#20: Post by HoldTheOnions »

TomC wrote:This whole article cited is based on industrial roasting, not artisanal. It's like comparing apples to walnuts.
NoStream wrote:For reference, he's working on a 15 kilo Probat with a modified fan system that gives him quite a bit of control and headroom.
I have a 24oz, by volume, Poplite with an extruded polyvinyl chloride base, precision Brinkmann temperature gauge accurate to within +/-15%, 4 amp Stinger blower, dual HF speed control, and machined tapered steel mini-easter basket chimney with built in handle. Apples to walnuts my hiney.