ozzie_jim Senior Member Joined: 28 Apr 2006 Posts: 4 Location: Sydney Expertise: Just starting
Posted Sun Aug 29, 2010, 3:51pm Subject: Air in the coffee roasting process
I have a new 10kg drum roaster that I'm playing with. After doing a number of "standard" training roasts in my roaster as shown to me by the seller of the roaster I tried to experiment with air flow on a Columbian Supremo bean.
First I did 3 roasts with little or no air to 2nd crack and just before and after 2nd crack.
Then I did 3 roasts with maximum air to exactly the same temperature profile. I added more heat to maintain the profile curve and compensate for the extra air.
The beans roasted with no air were rancid and bitter. After each taste I looked like I'd sucked on a lemon.
The beans roasted with lots of air were full bodied with a nice finish. Good for milk based drinks.
Has anyone had any similar experiences? What is the air doing to produce the better flavours?? It seems to me that the air is as important as the heat, if not more important.
ozzie_jim Senior Member Joined: 28 Apr 2006 Posts: 4 Location: Sydney Expertise: Just starting
Posted Tue Sep 14, 2010, 3:00pm Subject: Re: Air in the coffee roasting process
Only through trial and error. Adding air definitely gave me a smoother blend for all the beans I trialled. I went through about 150kg of beans so it was a fair test.
Dave7779 Senior Member Joined: 12 May 2009 Posts: 20 Location: UK Expertise: Just starting
Roaster: Diedrich IR-2.5
Posted Tue Sep 14, 2010, 3:18pm Subject: Re: Air in the coffee roasting process
So i take it you are leaving the airflow open fully now?
There must be a reason for changing the airflow, did you change the airflow during the roast process ie opened full to first crack then backing off the heat and limiting the airflow after this?
Maybe the water content of the beans has something to do with it, if the water evaporated and couldn't escape then maybe that was what made the beans taste bad. So many questions and not enough answers......
ozzie_jim Senior Member Joined: 28 Apr 2006 Posts: 4 Location: Sydney Expertise: Just starting
Posted Tue Sep 14, 2010, 3:42pm Subject: Re: Air in the coffee roasting process
As much as possible we leave the air open. The goal is to raise the temp by 12 degrees per minute to first crack then 4 degrees per minute up to 220 celcius for Arabica beans. While there's enough heat going in from the gas heating we leave the air as open as possible.
My thoughts are that the extra air "roasts" the beans better all the way through, like an air forced oven. With less air maybe it boils/bakes them and not all the way through. Who knows - they just taste much better.
germantownrob Senior Member Joined: 2 Dec 2007 Posts: 2,017 Location: Philadelphia Expertise: I love coffee
Espresso: Duetto 3, A Dead Oscar Grinder: Vario-W, Preciso w/Esatto,... Drip: Brazen Roaster: Diedrich IR-1, HT B
Posted Tue Sep 14, 2010, 4:29pm Subject: Re: Air in the coffee roasting process
I am still waiting for my Diedrich roaster so all I have to add is theory so take it with a grain of salt. Air flow gives you convection heat, while beans are in the air the air heats them 360 degrees, with out air flow the heat is from the drum surface mainly. First crack is where I see people on utube start air flow and towards the end of roast increase it to full power to aid in smoke and chaff removal. When profiling a certain bean you may want air flow at different times such as the drying phase.
Dave7779 Senior Member Joined: 12 May 2009 Posts: 20 Location: UK Expertise: Just starting
Roaster: Diedrich IR-2.5
Posted Wed Sep 15, 2010, 4:58am Subject: Re: Air in the coffee roasting process
hmm seems a lot of guess work and no one really know how/why it effects the actual roast or when it should and shouldn't be used. From what Ozzie said leaving it closed the entire time isn't a good thing but leaving it open seems to produce better coffee, now if we knew how and why it affected the beans and what reasons you would have for changing the airflow, it might make our roasting experiences more productive. Lets hope someone more in the know reads this and enlightens us all.
Dave7779 Senior Member Joined: 12 May 2009 Posts: 20 Location: UK Expertise: Just starting
Roaster: Diedrich IR-2.5
Posted Wed Sep 15, 2010, 6:08am Subject: Re: Air in the coffee roasting process
Which diedricht are you getting?
I recently bought the Toper 3Kg roaster, I have been working long and hard to figure it out and although I have been getting some nice coffee out of it I'm not really getting great coffee.
He goes on a little bit but at about the 8.30 mins mark he is talking about the airflow, he mentions the need at first crack to get the airflow open to release the CO2 build up in the machine and release the pressure. My issue with this is that by increasing the airflow the temperature inside the drum will drop, does this mean that there is a need to increase the burner temps? also you never see if he changes the airflow at any other point or if it was fully off to begin with.
My normal roast at the moment i start with a 245c charge temp then drop the beans, this gets me to 1st crack at about the 10 min mark i then keep an eye on the beans until i have an even roast then drop them for cooling normally around the 13-14min mark. I don't have a bean probe and this is an ongoing argument I'm having with toper(although they are ignoring me) because i specified the machine was to have one. I'm guessing the beans are being dropped at about 215c but again without the bean probe i cant be sure, the drum temp is reading about 230-240c though. As you can see i don't mess with the airflow at all and it is always fully open, but if I was to close the vent at the start then open to finish then I would expect to lose heat and maybe stall the roast at the first crack mark. Again I get to a point of maybe understanding then end up with more questions.
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