How does high airflow strip flavor from the bean?

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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drgary
Team HB

Postby drgary » Jul 20, 2018, 4:16 pm

I'm interested in what happens when too high airflow strips flavor from coffee. Is there a stripping away of moisture? Are the beans baked? Here's one of the victims.

Image

This was the thread where that photo exists:

Constant high airflow doesn't seem to work with my roaster

This is the roast profile. The level of the flick doesn't explain how bad this coffee tasted.

Image

In a more recent thread, pro roaster Christopher Feran wrote this:

archipelago wrote:Another thing I see mentioned here is about how "high airflow strips moisture". Most modern fluid bed roasters allow control of airflow (Lorings, which are hybrid roasters, use convection to cook but really are low airflow relying on the paddles to agitate and loft the coffee). Older Probats and many drum roasters don't allow airflow control and have pretty low airflow — this is like setting your air to a 'minimum' setting using the lighter trick and leaving it alone. I reckon that the issue with too high airflow has less to do with wicking of surface moisture (there isn't much) and more to do with the amount of BTUs you have to shovel into a roasting environment to compensate for the lack of radiant heat. You'll have a lower ET in a high airflow situation, with higher BTU at the burners (and thus likely a hotter drum) than if you have a lower or more balanced airflow settting (requiring lower flame while maintaining higher ET)


I asked him what was the cause of stripping flavor and aroma with high airflow. Here's his response:

archipelago wrote:Definitely a worthy inquiry, I absolutely believe you — my guess is that it's actually baked... that the bean pile experiences a drop in temperature due to the airflow, rather than allowing a pillow of radiant heat in a lower airflow environment to continue the cooking at the endothermic flash event


If I follow his reasoning, even though the airflow is constant at a speed that takes me to 1C fastest at maximum burner setting, I can see that a lower burner would bring more air to the beans to get the heat to the surface, which might heat the surface but not penetrate. Does a bean care how heat is applied? Taste says yes. Do others agree it's a way of baking beans instead of stripping moisture?
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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spromance

Postby spromance » Jul 20, 2018, 10:10 pm

drgary wrote:...even though the airflow is constant at a speed that takes me to 1C fastest at maximum burner setting...


I remember your thread from a while back, which puzzled me a bit because of my own conflicting thoughts about how level of (constant) airflow affects flavor quality. Quick question for you before throwing out some thoughts of my own: when you say high airflow and max burner that takes you to 1C fastest, does this mean across all your roasts for a given bean? i.e. In the above profile you're getting 1C at 10:32 - is that the quickest you ever get to 1C? Or the fastest you can get to 1C when using a high airflow setting on your roaster?

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drgary
Team HB

Postby drgary » Jul 21, 2018, 12:01 pm

Thanks for asking. There was a test across roasts for a single bean with the burner set on high. The airflow setting that got me there fastest was the one set as a default. This was a later roast with the airflow at that setting and where I'm adjusting only the gas, once I turn on air after about a 1:30 soak with no air.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

jayc

Postby jayc » Jul 21, 2018, 5:25 pm

What flavors are you tasting?

Perhaps the 4 minutes of flat ROR is affecting the flavor?

I find my roasts taste like paper/cardboard if the ROR is flat for too long. Even a minute seems to affect the flavor.

Did you try the same bean, same airflow with the exception of lowering your gas? Or is it the airflow that is effecting your ROR?

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another_jim
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Postby another_jim » Jul 21, 2018, 5:35 pm

I think are partially barking up the wrong tree.

Fluid bed roasters on the small end and industrial roasters on the large end have higher airflows than an drum roasters. The historical line of all large commercial roasters from the original 1940s thermalo have had higher airflows. Lab roasters that can duplicate any profile are based on high air flows; Probat will gladly sell you the their 100 gram model for 20K.

But all these require that high air to roast the beans -- they are blowing hot air

Then there was the catastrophically awful "profile control" drum roaster from about 2007, built by a company I'll leave unnamed (but that began with Am...). The design genius behind this roaster decided that if the bean temperature was rising too quickly, the best solution was to blow in cold air. Back in the day I was using my PIDed air roaster, I had to reengineer it so that it never reduced the supply air temperature. Any drop whatsoever created a blind tasteable drop in roast quality; letting the actual bean profile run ahead of the target was better than dropping the environmental temperature.

So here's my take: The Am... dropped the ET far and fast in a high thermal mass drum roaster, and that killed the taste. I dropping the ET very slightly in a low thermal mass air roaster, and did the same. Most drum roasters allow for gradual and small drops in the ET without much harm; but basically, any drop in the ET detracts from the taste. Drum roasters require that the heat be checked when approaching the first crack. I get better roasts doing this as gradually as possible. The effect of airflow on the ET varies from machine to machine; but to my mind keeping ET drops minimal is the key.

I think this refusal to futz around frantically with the ET is more important than all the recent ROR-numerology. There is no perfect profile; but there are spoiled roasts from desperately trying to get one.
Jim Schulman
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Case17

Postby Case17 » Jul 21, 2018, 9:05 pm

drgary wrote:I'm interested in what happens when too high airflow strips flavor from coffee. Is there a stripping away of moisture? Are the beans baked? Here's one of the victims.

<image>

This was the thread where that photo exists:

Constant high airflow doesn't seem to work with my roaster

This is the roast profile. The level of the flick doesn't explain how bad this coffee tasted.

<image>

In a more recent thread, pro roaster Christopher Feran wrote this:



I asked him what was the cause of stripping flavor and aroma with high airflow. Here's his response:



If I follow his reasoning, even though the airflow is constant at a speed that takes me to 1C fastest at maximum burner setting, I can see that a lower burner would bring more air to the beans to get the heat to the surface, which might heat the surface but not penetrate. Does a bean care how heat is applied? Taste says yes. Do others agree it's a way of baking beans instead of stripping moisture?


I have to say, these 'baked' beans answers are very hand-wavy. What in the hell does is even mean in a technical sense???

One would think a couple things come to mind:
1. High air flow results in over oxidation of the beans due to high O2 flux.
2. Voltaile aromas are evaporated more easily due to the high flux.
3. Potential discrepancy btw thermocouple and bean mass. High air flux should help make the bean mass temp and thermocouple temps closer to each other, meaning that the baseline reading on which everyone is calibrated is off.

The question of rate of heat transfer (conduction through the bean) versus convection at the surface from air, is an interesting one. Typically though, i always though high air flow improved the evenness of cooking, and therefore conduction is the slow step.
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Almico

Postby Almico » Jul 21, 2018, 11:19 pm

I just did a fast/hot/FC+roast on my air roaster:

Image

Here's a bean from the roast:

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RoastRite #s 47/47. 15.8% moisture loss.

I assure, this coffee is anything but tasteless...

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drgary
Team HB

Postby drgary » Jul 22, 2018, 12:11 am

Of course I'm not implying an air roaster is bad. I've tasted lovely air roasts. Maybe more airflow and less application of heat is out of balance and bakes the beans.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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Almico

Postby Almico » Jul 22, 2018, 12:32 am

I know very little about drum roasting, but I would really like to learn. This airflow you're talking about, is this ambient air or hot air from around the drum?

I just got copy of an old Diedrich users manual where it says to open the air 100% for a minute or so (around yellow) when you see chaff being released through the glass. This is to blow the chaff out before it gets broken up or sticks to the "oily" beans.

If this is outside air, how does it not tank the RoR? It would be like opening a window in the sauna.

The profile you posted above looks like a classic baked roast. Long dry, long, flat RoR Maillard with a crash and flick for good measure. It's hard to believe there is any sweetness left in the beans and likely tastes like roasty aspirin.

OldmatefromOZ

Postby OldmatefromOZ » Jul 22, 2018, 2:03 am

Almico wrote:I know very little about drum roasting, but I would really like to learn. This airflow you're talking about, is this ambient air or hot air from around the drum?

I just got copy of an old Diedrich users manual where it says to open the air 100% for a minute or so (around yellow) when you see chaff being released through the glass. This is to blow the chaff out before it gets broken up or sticks to the "oily" beans.

If this is outside air, how does it not tank the RoR? It would be like opening a window in the sauna.

The profile you posted above looks like a classic baked roast. Long dry, long, flat RoR Maillard with a crash and flick for good measure. It's hard to believe there is any sweetness left in the beans and likely tastes like roasty aspirin.


Edit: I know nothing... :roll:

Yeah ive just seen you were looking at Diedrich, google image search diedrich profiles, complete opposite to decline ROR / rao style roast...yes the 100% air would flatten ROR at yellow, for a slow ramp up into FCS and a short finish, classic SS/FF roast, ive never had anything ive liked roasting that way.

I agree 100% with last paragraph, looks like way too much heat in the roaster, ROR can not be reigned in and the seeds experience dramatic decline due to this energy.

Im finding out slowly that many people like crashed/ baked roasty coffee and that it is possible like you to roast well into 2nd crack with a smooth crashless declined ROR. Dark roasts are not inherently roasty or bitter!