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  • Harrar Roast Profile

    I've gone through about 1.5kgs of Harrar in my PID controlled popper, without much success (ie, not what I expected).

    I was getting splits in the beans, tipping, a wrinkly surface and a slightly charred taste.

    After digging though the threads here, it seems my steep profile early in the roast may be to blame. So I tried a "ramp roast" last night - much better colour, no wrinkling and minimal splitting/tipping. Smells better too.

    Pretty excited to see how it tastes in a few days.

    I'll post a profile later

  • #2
    Hi MrJack,

    Thanks for letting us know. What was the previous steep profile and what profile did you try that worked better? As in what times and temperatures?

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    • #3
      Did 2 batches of Harrar Longberry in my wing-it drum roaster yesterday. Gentle heat for first 3min, then slow but steady up to 1C @ 14-15min - surprisingly muted 1C, and very little exothermic activity (tendency to stall if one usually backs off the heat a bit during 1C, as I do) - hit a quiet 2C 5min later and dumped ASAP.

      Not the easiest bean to roast in my limited experience, I'd love to hear how more experienced folks have dealt with it.

      Comment


      • #4
        Re: Harrar Roast Profile

        As exothermic means PRODUCING heat (just like fire) I doubt it would cause the stalling. In effect, the beans heat themselves. According to my reading, the exothermic phase is short, at the onset of 1C and is followed by an endothermic phase (heat absorbing -where stalling can happen - if your heat input is infufficient to drive the chemical reaction).

        There are three things that can happen to the heat you apply - it raises the temperature of the beans, it melts or vapourises something in the bean and/or it drives an endothermic reaction and is absorbed without raising the temperature (Literally the heat energy becomes part of the chemicals produced in the beans).

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        • #5
          Looks like it's back to school for me! :-(

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          • #6
            Hi Chokkidog, thanks for the info. My roaster is a rotating billy-can over a 2 ring gas burner - I posted some pic's a few months ago. I'm using an IR thermometer at present.

            I usually back off the heat as soon as 1C starts until the temp starts to dip a little (2-3min later), so that the roast doesn't rush into 2C too quickly, the temp remains stable for several minutes. My understanding of an exothermic process is that it produces heat - therefore if I keep heating the roast at the same rate during 1C it will accelerate the rate of heating, making it difficult to control. From my reading it seems a good idea to extend the interval between 1C and 2C.

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            • #7
              Originally posted by MrJack View Post
              As exothermic means PRODUCING heat (just like fire) I doubt it would cause the stalling. In effect, the beans heat themselves. According to my reading, the exothermic phase is short, at the onset of 1C and is followed by an endothermic phase (heat absorbing -where stalling can happen - if your heat input is infufficient to drive the chemical reaction).

              There are three things that can happen to the heat you apply - it raises the temperature of the beans, it melts or vapourises something in the bean and/or it drives an endothermic reaction and is absorbed without raising the temperature (Literally the heat energy becomes part of the chemicals produced in the beans).

              Actually... Exothermic refers to the RELEASING of heat.... not the production of heat. And since heat is energy and energy must come from somewhere... i.e. from the bean itself... it just makes sense that as the bean loses energy by releasing its heat that it requires more energy input in order to keep the process going. And... by the way... there does happen to be a second exothermic phase following the one you pointed out... it's called Second Crack

              And... just my own humble opinion perhaps but methinks you would be playing silly buggers to challenge Chokkidog on his roasting knowledge

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              • #8
                Hi haba,
                Looks like I misread/misunderstood a statement in an article some time a go and have been wrong ever since.8-(
                Like my teachers used to say, revision is always good, doh! The post sort of works if you swap the terms around but I deleted it
                so my poor form doesn't confuse others.
                I've found that 3.5 to 5 minutes between 1st and 2nd crack gives me the best results. (mostly 3.5-4)
                I reduce my heat at 180* - 190*, depending on bean/profile/charge weight then reduce airflow by 1/3, from 195* -205*, to control temp loss and develop body, 205* is just before the roast starts to heat up again. Airflow is 100% from just before the end of 1st crack ( 205*) until the end of the roast.
                A further reduction in heat down to 50% or as low as 30% occurs about 215*, (give or take once again, depending on the same parameters bean/profile/ charge weight). Heat is turned off just before end temp is reached using bean mass heat to finish the roast.


                Ya learn something everyday!
                Last edited by chokkidog; 30 January 2013, 11:15 PM. Reason: body comment

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                • #9
                  Originally posted by Vinitasse View Post
                  Actually... Exothermic refers to the RELEASING of heat.... not the production of heat. And since heat is energy and energy must come from somewhere... i.e. from the bean itself... it just makes sense that as the bean loses energy by releasing its heat that it requires more energy input in order to keep the process going. And... by the way... there does happen to be a second exothermic phase following the one you pointed out... it's called Second Crack

                  And... just my own humble opinion perhaps but methinks you would be playing silly buggers to challenge Chokkidog on his roasting knowledge
                  I'm not challenging his roasting knowledge (I'm definitely a beginner), only his chemistry and thermodynamics (with which I have a little more experience). I apologise if the language came across confrontational; I was writing quickly via the tapatalk app on my phone which makes self editing painfully slow.

                  The part about which phase is endo/exothermic I got from https://www.sweetmarias.com/library/...e-degree-roast, which seems to be quite a reliable reference. This reference has a lot more information (in a much less engaging format!).

                  Releasing, producing, it's semantics really. And it's not referring to the bean, but to the chemical reactions. The heat is released from the bonds in the chemicals which are broken during the roasting process. The effect is that heat is actually produced within the bean. If the surrounding temperature is higher than that of the bean, then the bean will heat up, otherwise it will release the heat.

                  The act of releasing heat does not necessarily mean the bean will cool (as this depends on the relative rates of heat production and heat transfer from the bean); the bean cannot cool at all if the surroundings are kept at a higher temperature (heat can only flow from a higher temperature region to a lower temperature region)

                  Anyway, we seem to have digressed. Below is an image of the PID profile used for the roasts last night. While I didn't log the bean temp, it appeared to be lagging 5-10 C below the setpoint temperature in the middile of the roast, and only ever got to about 218C (only a 900W popper).

                  Click image for larger version

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                  Last edited by MrJack; 30 January 2013, 11:33 PM.

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                  • #10
                    And then there is the endo / exo reversal point...........
                    Thank you Vinitasse for your kind words but I'd be the first person to challenge my roasting knowledge!!
                    And I'm more than prepared to eat humble pie. And no MrJack I didn't think you were being confrontational at all.
                    But I learnt something else in my reading this evening!.........
                    If I hold down the 'option/alt' key on my mac and press zero I can make a degree symbol! 205º ! Voila!
                    But I suppose you all knew that too ;-)

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                    • #11
                      Needs some serious thought this thing about 'endo/exo thermic' conditions in the roast and just how they manifest and influence
                      the nature of the roast profile.
                      In lay terms, there doesn't seem to be any debate over what the two terms mean; endo=absorbing heat and
                      exo=producing heat (and by nature if something is producing heat, it's giving off heat ).
                      So if a roast goes from endothermic to exothermic in the immediate lead up to and the start of, 1st crack, then the beans
                      are producing heat which is then removed by exhaust airflow, therefore cooling the bean mass at the exothermic reversal point,
                      when the beans are no longer producing heat.
                      If no changes are made to heat input or airflow then the roast would tend to 'stall' or at least have a decreasing rate of increase.
                      A 'lack of exothermic reaction' would mean that the beans retain their heat from endothermic action and the roast wouldn't stall.
                      How am I doing? Maybe I wasn't so wrong after all? Is there logic in my thoughts, or should I go to bed?
                      I still have a copy of the deleted post if anyone wants to re read it, complete with edited º symbols! :-)

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                      • #12
                        Re: Harrar Roast Profile

                        Sorry, but you've still got it back to front.

                        The only way the beans can lose heat to the air (irrespective of what reaction is going on) is if they are hotter than the air.

                        So long as you maintain the air temperature greater than the bean temperature then heat will transfer from the air to the beans.

                        Now, when the beans are undergoing an endothermic reaction, some of the heat is used to fuel the reaction, instead of heating the beans. If you want to maintain the rise in bean temperature then you need to supply additional heat - equivalent to that consumed by the reaction. Depending on your setup, this could mean a higher temperature, or faster airflow.

                        Make sense?
                        Last edited by MrJack; 31 January 2013, 01:05 AM.

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                        • #13
                          A very informative discussion - thanks guys. To clarify the whole exo/endo thing. I'm more familiar with the use of the term exothermic in chemistry - the use of the word releasing is ambiguous in this sense, because an exothermic reaction PRODUCES heat/light, therefore the meaning of the word release in this context is "give off" and not "lose".

                          Endothermic reactions absorb heat from the environment.

                          During the onset of 1C coffee beans are exothermic, a reaction within the bean PRODUCES heat therefore if heat is applied at the same rate from outside (the heat source) the rate of heat gain will accelerate during the exothermic phase and the interval between 1C and 2C would be very short. This is what I expect beans to do, and I usually cut one of the gas rings until the system returns to endothermic, i.e. the bean mass temp starts to dip. Once this happens I relight the 2nd ring and the beans continue to heat steadily up to 2C.

                          The Harrar noticeably lacked the exothermic phase that defines 1C - they tended to stall if I reduced the heat as I usually do, and the the snap (energy release) was very soft.

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                          • #14
                            Nicely put.

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                            • #15
                              I've find it helpful to think of these reactions kinda like popcorn…
                              Heat em up for a while (endo) then they give it all back in a hurry! (exo). Just that coffee has a two stage process :-) So add heat into that popping stage - and it takes off like a rocket!

                              I've found generally that by ramping more heat in just before 1C (from 185º - love that shortcut chokki - save the 'deg' for another day!) can give a stronger reaction - but whether that tastes any good depends on the bean. So don't worry if 1C is quiet - if it tastes good!

                              I'm having some great results from this bean at the moment just using my normal gentle ramp profile, which doesn't give an explosive 1C - it just seems to be in the zone for those beans.

                              So keep cupping and let us know how they taste!
                              Matt

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