Professional roaster advice on RoR - Page 2

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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[creative nickname]
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#11: Post by [creative nickname] »

day wrote:so I finally met in person a local roaster I get most my green from. He is an awesome guy and I have a lot of respect for him and has won a few various roasting competitions. He told me that he waits until first crack and then almost cuts all heat off for about 45-50 seconds to switch from exothermic to endothermic (I may be remembering slightly wrong). And then he urns the heat back on and finishes.
I used to do this for some roasts on the USRC sample roaster, primarily when I was trying to achieve a fast ramp followed by a steady development phase with a reduced, and fairly constant, ROR. The drum has a lot of thermal mass so it continues to push the roast along for about a minute after you cut the gas completely. If you don't start the gas back up, ROR would stall before too long after FC-end. So if you want a fast ramp, followed by a steady 6F/min ROR for four minutes of development, this would be one of the best ways to achieve that on that equipment.

If you are targeting a steadily declining ROR, this would not be a way to achieve that. And if you have a roaster without a lot of internal thermal mass, I don't think this approach would help you achieve anything worthwhile. Frankly, after tasting the results of these sort of profiles side-by-side with a steadily declining ROR approach, I almost always prefer the results I get from the latter, so I rarely find myself cutting the gas and then restarting it anymore. What I still do, sometimes, is turn the gas off completely towards the end of development to get a nice steady taper in my ROR leading right up until drop.
LMWDP #435

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JavaMD
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#12: Post by JavaMD »

I must be the outlier here. with my Santoker 500 that I typically roast 450 grams of beans ... I slowly cut the heat down and increase the air flow through the roaster during the ramp phase and get a very nice slow drop in the ROR ... at first crack I leave the airflow alone and increase the gas for 30 seconds and then slowly back off on it till about 1:15 post first crack when I'll really cut back on the heat and increase the airflow. This way I get a very nice slowly declining ROR. My probes seem VERY responsive to my gas and air changes in the ET and MET probes. So I tend to believe them. If don't increase the gas to cover the endothermic cooling caused by first crack water vapor evaporating and cooling the beans ... my ROR drop is PROFOUND ... and I struggle to hit drop temps of 400F without baking the beans. Rao Discusses this "plummet" in the graft on page 45 of his book ... I really have to anticipate it and will have to turn my gas up to the level I used during the drying phase or a bit more to help "dampen out the plummet" .... different roaster I guess ... different probes ...
Interesting with some Ethiopian dry process beans (Klatch Gedeo Worka for instance)I do not see this plummet at all and do have to cut back on the heat at first crack to keep the ROR from rising ...

Steve

Zaneus
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#13: Post by Zaneus »

It ill be different for everyone. I roast daily on a 12kg probat P12 and i notice both a flick just before first crack, and a dip just after the onset. It all depends on my approach to the particular coffee and the kind of momentum going into ic. If my air temp is FALLING coming into 1c, that means ive put a lot of energy into the system leading up to 1c, and i wont see a flick, but i will see a dip. When my environment temp is RISING i'll see a flick and no dip. If my air temp is holding steady or rising at the same rate as my bean temp, i'll most likely see both a flick and a dip.

Coffeengineer
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#14: Post by Coffeengineer »

This thread has wandered into the exothermic first crack area so I thought to mention my experience - last time I tried this I had posts deleted from another forum! I was pleasantly surprised to see Rao referring to the endothermic flash at first and thought at last truth is coming out. I think the myth of exothermic 1C started with some coffee roasts done in a sealed calorimeter that do not reflect common roasting conditions of atmospheric pressure.
I roast in my own designed and constructed air roaster that has very low thermal mass with accurate fast thermometry. It is quite easy for me to calculate the power flow into the actual beans and I display that in real time. If I run a simple linear BT profile I get the apparent thermal capacity of the beans vs temperature. The usual plot has a smallish dip before first, possibly due to the ending of Mailard reactions that are a little endothermic, then quite a spike (+20% or more) peaking mid first then tails off heading for zero as second is entered. It does look like one is about to go into exothermic territory well into second but I always kill it before. The plot is different for different beans, but since I do not get very good results from a linear profile I cannot make simple comparisons.
I hypothesise that the endothermic phase in first is caused by the expansion of the beans and the consequent reduction in internal pressure within the bean.

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