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  • Originally posted by Javaphile View Post
    This is a misleading/incorrect usage of the term 'exotherm'. When something is exothermic it is giving off heat. Just because something is giving off heat does not mean it is cooling off. A perfect example of this and one that gives the lie to the use of the term in the quoted bit is when beans hit first crack (Which happens with-in the quoted temperature range.) they become exothermic. ie They give off heat. When this happens the temperature of the beans rises, not falls. Hence why it is so important to reduce the amount of heat being put into the beans so you don't get a runaway roast.

    A better phrasing would be: Once caramelization begins, it is very important that the coffee mass's temperature does not decrease or the
    coffee will taste "baked" in the cup.


    Java "Correct terminology matters!" phile
    I was away when this was posted and missed it entirely, until the other day.

    Java"correct"phile is quite right. I've read so much about endo/exothermic reactions over the past year that I glossed right over it and failed to pick up the error.

    Sorry about that.
    I know what Staub was alluding to but his use of terminology is a bit too relaxed, I agree.
    None of the dictionaries say that to 'exotherm' is to lose heat.

    An exothermic reaction is one that produces more heat than what is required to initiate the reaction.
    An everyday example is a burning candle, where the total heat and light energy produced is greater than the energy required to light it.
    A more interesting example is the freezing of ice. This exothermic reaction is used in viticulture to prevent frost killing new shoots in spring.
    By spraying water on the shoots, when the frost forms at 0°C ,the 'latent heat' produced by the freezing of the applied water
    stops the shoots from freezing! See pic 1&2

    But I digress, from all my reading it seems that the science of roasting is a relatively new pursuit and is lagging behind the sudden
    growth in home and boutique roasting that has occurred over the last 10 years. None of the material that I have read gives a definitive
    account of the complexity of endo/exothermic reactions which occur in the second half of a roast. The most promising looked to be in a book which I had to purchase…..

    It seems that beans start going exothermic when pyrolysis of sugar commences after the Maillard Reaction. In my roaster it seems to start around 180°C.
    Yesterday I roasted some Brazil beans and left the heat and air settings the same, from 130°C onwards, to see the difference to a normal roast
    where the heat is turned down a couple of times and the airflow is manipulated during part of 1st crack.

    From the photo there is a gradual acceleration of °RoR from about 180°C which continues until the second half of first crack.
    At approx 205°C there is a marked slowing of °RoR until approx 212°C, at which point it starts to accelerate again.
    It would seem that it is this phase (of slowing) where the roast is most likely to bake by going into a prolonged negative °RoR.
    i.e. flatlining from this point.

    What this all means in terms of when the reactions are actually happening I don't know, it's not that clear cut.
    If exothermic beans are releasing heat but the reaction slows there must be a point where the airflow removes more heat
    than what the beans are producing. Where does the energy required for bean expansion come from and how does that
    impact on exothermic reaction?

    It doesn't need to be understood but…………..

    I've got too much time on my hands. ;-D
    Attached Files
    Last edited by chokkidog; 23 October 2013, 11:31 PM.

    Comment


    • Originally posted by Jiffy View Post
      Hey Matt, Love the look of this profile, just wondering why you pre heat on some of your roasts and not on others/
      Hi Jiffy
      Pre-heating is a fairly new development for me that happened when I went to 700g batches. My 350g roasts I did from cold. Just found with the bigger batches they were taking tooooo long from cold - the pre-heat managed to take away 1-2 minutes without requiring huge increases in gun temp - potentially creating tipping etc in the fuller pan
      Matt


      And great work on the Exo-Endo explanation Chokki - there are some amazing things going on inside those little suckers! The strength of that 205° heat-sink always surprises me - you seem to be going in wayyy too hot - but then RoR suddenly plummets to 2-3°!

      Comment


      • Originally posted by DesigningByCoffee View Post
        PS this is the next resting variation - slightly more tuned start - faster 1c-2c ramp
        [ATTACH=CONFIG]4624[/ATTACH]
        I'm into this batch now (I ended up offloading the second bag of the Bandit - time for a change!) and now we're really getting somewhere!

        This batch is a blend of Uganda & MMG - and with this profile there is huge fruit - I'm thinking big juicy white nectarines - and not just a hint - but like slurping down a whole necterine! Quite unusual flavour, and nothing at all like the deep cocoa I've come to expect from a blend with the uganda in it. The syrupy sweetness is the MMG through & through - and awesome crema.

        When I looked at the roast colour I thought initially that I had under-roasted it (see pic) but although it is still quite sharp and bright, there is very little sourness. I believe the overall shorter roast time has led to this lighter colour - but it also will hopefully give some headroom at the end to go darker while still maintaining the fruity origin characteristics. I did drop this quite early - it was certainly before 2C started.

        But what I'm really pleased about is that while I haven't seen cocoa for a while, the hint of gritty/soapy flatness has disappeared by shortening the roast time to 1C a fraction and upping the heat input just after turning point, and the fruits have exploded. If I can now just bring in some cocoa through a slightly higher drop point, I'll be stoked

        So next round - maintain this profile, but take a little darker - maybe drop at 223° rather than 221°, just on 2C and see what happens.

        Happy roasting all!
        Matt

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        • Update:
          Just finishing the above bag. Smoothed up considerably, but still maintained the fruitiness, though not as eye popping as the first day opened! Still a little on the sharp side as a doppio, but very nice in a FW as it aged - due to the acidity and lighter roast it didn't cut through milk so well early on.
          The next batch is the same blend, same basic profile but taken 2° higher - just at the start of 2C. Will be into that tomorrow, so not as long a rest as I'd like (only 3 days) but we'll see how it shapes up

          Cheers Matt


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          • Originally posted by DesigningByCoffee View Post
            The next batch is the same blend, same basic profile but taken 2° higher - just at the start of 2C. Will be into that tomorrow, so not as long a rest as I'd like (only 3 days) but we'll see how it shapes up

            Cheers Matt


            [ATTACH=CONFIG]4700[/ATTACH]
            And here is a photo of the browns - noticeably darker than the previous batch, but still nowhere near dark roasted. CS8-9 ish?
            Smelling great on my light table!

            Will be into those this morning…

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            • Originally posted by chokkidog View Post
              A more interesting example is the freezing of ice. This exothermic reaction is used in viticulture to prevent frost killing new shoots in spring.
              By spraying water on the shoots, when the frost forms at 0°C ,the 'latent heat' produced by the freezing of the applied water
              stops the shoots from freezing! See pic 1&2
              Water freezing is a phase change (i.e. a physical process), there is no chemical reaction happening. So this would be best described as an exothermic process.

              Perhaps this is what saves the shoots if they have a lower freezing point?

              With regard to the rest of your post, I think you have highlighted an important distinction in what is meant when 'first crack' is described as exothermic.
              I haven't read any original research, but I presume that the net effect of the reactions is exothermic i.e the reactions release heat. This is distinct from the bean mass releasing heat, which can only occur if the temperature of the surroundings is lower than the beans.

              However, I suspect that there are actually a number of reactions or chain reactions occurring, and whether the bean mass is able to lose heat would affect reaction equilibria and/or favour the rates of certain reactions over others (the end result being a different mix of chemicals post roast).

              These kinds of reaction mechanisms are (to my understanding) notoriously difficult to study - so it would not surprise me at all if only some reactions had been identified or if the process was only understood in a general sense (as far as is required for practical application).
              Last edited by MrJack; 1 November 2013, 12:15 PM.

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              • Do your research........... I don't post statements like that without being sure of my facts.

                Have to go out now but will post references later.
                Or you could just check out some of these..........


                Principles of Frost Protection

                https://www.google.com.au/search?cli...GeTC8ge24IDICw

                roll eyes :-D

                Cheers

                p.s. ucdavis is the University of California Davis campus, probably the world's leading seat of viticulture knowledge.
                I also worked at a Central Victorian vineyard ( now called Bress) and installed an ice forming frost protection system there, based on the above principles.


                Your credentials are..........?

                p.s. it cost a truck load of money, a full 2nd irrigation system, completely independent of electricity supply, in case of blackout.
                The owner did plenty of fact finding first.

                I'm also in a hurry so missed your bit about chemistry........ you are the only one who mentions the freezing of water and chemical reaction
                in the same sentence....... I certainly didn't.
                Last edited by chokkidog; 1 November 2013, 12:10 PM. Reason: add p.s.

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                • How embarrassing!
                  Ignore my (not- so-ninga edited) comment about freezing absorbing heat!
                  Teach me to post whilst in bed, 3 minutes after waking up. Haha.

                  My response was really triggered by your use of the term 'reaction' which respect to freezing, which I generally would associate with chemical reaction (and, perhaps erroneously, assumed others would also).

                  My credentials... good enough that I shouldn't make such a slip

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                  • Originally posted by DesigningByCoffee View Post
                    And here is a photo of the browns - noticeably darker than the previous batch, but still nowhere near dark roasted. CS8-9 ish?
                    Smelling great on my light table!

                    Will be into those this morning…

                    [ATTACH=CONFIG]4704[/ATTACH]
                    Smokin!
                    Just cracked into this new batch. 50/50 mixed with beans from the last bag, as there was still some in the grinder, and hooley dooley! Big cherry ripe as a FW. Even my good lady wife responded before I said anything about the new bag with "Wow - chocolatey!"

                    Very, very smooth & balanced – we'll see as a doppio…
                    Matt

                    Comment


                    • Originally posted by MrJack View Post
                      How embarrassing!
                      Ignore my (not- so-ninga edited) comment about freezing absorbing heat!
                      Teach me to post whilst in bed, 3 minutes after waking up. Haha.

                      My response was really triggered by your use of the term 'reaction' which respect to freezing, which I generally would associate with chemical reaction (and, perhaps erroneously, assumed others would also).

                      My credentials... good enough that I shouldn't make such a slip
                      Semantics......
                      Chemical reactions aren't the only ones around, there are things called physical reactions too.
                      All the references I read used the term Exothermic Reaction, not one called it a 'process', no matter what example was being touted.
                      By referring to the freezing of water as an exothermic reaction is correct and 100% in line with published data.

                      Comment


                      • Matt, you have gained really good control over your profiles. Steve82's profiles are looking really smooth too!
                        Not only your beans are smoking' !
                        Do you intend to push a roast a bit darker? It looks like you still have a few seconds to play with.

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                        • Thanks Chokkidog.

                          Matt I really like the look of your profile in post 154, just on looks my favourite to date.

                          I have been working on having to eat my own words in regards to pre blending. I have been trying the method, maybe it was suggested by chokkidog? about sealing them up for a while before roasting. So one week in a ziplock bag seems to result in a very even roast and bean behaviour while roasting. The taste has been very good also. I doubt I would pick the difference in a blind test, if i could be bothered.

                          Progressively roasting lighter each time, stepping away from the brink of second crack. My brewing temps have gone back up around the 93 - 94 mark, very sweet shots ( once rested 7 to 10 days) excellent punch in milk, more fruits and floral are preserved, but early on there is way to much acid for espresso, but produces very lively and delicious flat whites, double in 160ml cup. I made one yesterday for a guy doing a quote for some work on the house, regular coffee drinker, requested 2 sugars, I told him I put sugar in it, I lied...he said he was blown away and had never tasted coffee like this...another palate re - educated (briefly).

                          I have found getting the right balance in developing the roast in the maillard zone and the development between FC /
                          end of roast is key. Giving up to much moisture early on and dragging out the end can have very bitter results.

                          The profile and beans pictured are a good 3 to 4 degrees prior to first scouts of second crack, still a nice sheen and puffiness about them and I get no oil spots. This was 150g central, 50/50 G.hueh/Nica DT, 150g Rwanda, 100g Sulawesi Blue.

                          happy roasting all

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                          • Originally posted by chokkidog View Post
                            Matt, you have gained really good control over your profiles. Steve82's profiles are looking really smooth too!
                            Not only your beans are smoking' !
                            Do you intend to push a roast a bit darker? It looks like you still have a few seconds to play with.
                            Thanks Chokkidog
                            I actually had a local fella come over the other day who's a commercial roaster - he was quite impressed by the control on the ole corretto I think!
                            I have gone a little darker here - this batch was just on 2C - but certainly do have room to play if I do some centrals that like it darker. I'm just really thrilled how this batch has such good balance of flavour, acidity and cocoa punch. Seems like that last degree or two at the end really just builds the flavours…
                            Might try and extra 1° next time - just for fun!
                            Matt

                            Comment


                            • Originally posted by Steve82 View Post
                              Thanks Chokkidog.

                              Matt I really like the look of your profile in post 154, just on looks my favourite to date.

                              Progressively roasting lighter each time, stepping away from the brink of second crack. My brewing temps have gone back up around the 93 - 94 mark, very sweet shots ( once rested 7 to 10 days) excellent punch in milk, more fruits and floral are preserved, but early on there is way to much acid for espresso, but produces very lively and delicious flat whites, double in 160ml cup.

                              [ATTACH=CONFIG]4706[/ATTACH][ATTACH=CONFIG]4707[/ATTACH]
                              Hi Steve
                              This is exactly what I found too with batch #154. Slightly too sharp for espresso, but nice and smooth in FW - but not overly grunty IMHO. I just wanted a little more. Would probably be perfect for filter though?
                              The extra couple of degrees though has really made a difference - from day 3 it is really powering on. So maybe keep that profile, and try adding 1° to the end each batch - see what happens!

                              Looking forward to the next brew already!
                              Matt

                              Comment


                              • Originally posted by chokkidog View Post
                                Semantics......
                                Chemical reactions aren't the only ones around, there are things called physical reactions too.
                                All the references I read used the term Exothermic Reaction, not one called it a 'process', no matter what example was being touted.
                                By referring to the freezing of water as an exothermic reaction is correct and 100% in line with published data.
                                While it is true that the term 'physical reaction' is acceptable, I can't say I've ever come across it in anything outside of chemistry textbooks. I have never heard it used in a professional context, but then, I am not an academic. I don't recall ever having heard the phrase 'exothermic reaction' used to describe freezing.

                                'Process' is a much more general term than reaction and, outside of the context of chemical reactions, much more frequently used.

                                In my opinion, referring to a phase change and a chemical reaction, in the same paragraph, as examples of "exothermic reactions", is just confusing the issue. But I realise that is only my opinion.

                                Comment

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