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Thread: Dark spots on the roasted beans?

  1. #1
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    Dark spots on the roasted beans?

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    I just finished my first roast. Im so glad to have got started finally!

    2 cups of Kenya AA, in a collander sitting on a S/S saucepan. XU1 heat gun.

    Everything seemed to go pretty fine, I used the high heat setting, and stirred constantly with a s/s whisk.

    First crack started at 11 mins, and second crack seemed to start at about 17 minutes, intensifying at about 18. I stopped at 18:30, and did about 2 minutes of bean juggling to cool in an afternoon seabreeze.

    The colour is uniform deep brown (and the look the same colour as the Vittoria in my grinder).

    When I was sorting through the beans, I noticed little spots/pits on the beans. some beans had 1, some 2 or 3. it seems to be the majority of the beans (I wont say all). Can anyone suggest what I did wrong?

    The only thin I can think is that they were semi burnt from hot air coming back through the holes in the collander? I dont know.

    2 hours on, and after sealing them in an airtight container, there is a lovely coffee smell when I crack the lid, but they dont smell burnt.

    Any advice?

  2. #2
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    Re: Dark spots on the roasted beans?

    Im still in my heat gun roasting infancy, but the spots you mention sound a bit like what Ive heard others call divots. The explanation for these was the beans expanding to quickly and structurally something had to give. Generally in my experience these spots are little potholes that are almost perfect circles. Im assuminng these divots can be prevented by a slower more even application of heat.
    The other black mark I have achieved :) are burnt tips ie tipping. Apparently if the heat is a bit too high the first part of the bean to give out is the thinner more easily burnt tips. Im not sure if tipping relates to the incorrect application of heat at a certain stage of the roast or is just simply an indication of roasting at too high a temperature from the start.
    Either of these traits, while not being a desirable outcome, have not lead to a massive degeneration in the ultimate taste of the coffee in the cup.

  3. #3
    TC
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    Re: Dark spots on the roasted beans?

    I heard that they were possibly created by alien spacecraft ;)

  4. #4
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    Re: Dark spots on the roasted beans?

    The important thing is the taste even if they look like a dogs breakfast ;D

    The spots are probably the bit of the outer shell comming off during roasting.

    Cheers
    Rich

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    Re: Dark spots on the roasted beans?

    Called "hot spots";

    Much more likely to occur on badly graded or non uniform sized green beans (ie beans of a lower "graded" or "cheaper" quality...non uniform density) OR, really badly managed roasting;

    However this also occurs with well graded good quality coffee;

    Ignoring "quality", density, and uniformity of beans, the formation of hot spots is related to intensity of the heat, the way it is applied, the speed at which the hot air can escape from the roasting environment, and the speed & type of agitation the beans are subjected to during roasting (which is still to do with the heat and how it is applied).

    It could be that the beans were not agitated enough or too slowly, and any pre-existing "imperfections" in the beans became hotter than the rest of the bean because of the way the beans lie, and the length of time they spend, against the side of the roasting drum / collander.....

    Ergo, it has to do with evenness/quality of roast VS uniformity and grading of beans.

    There will always be some of this present even with well graded coffee that is well roasted, due to the physical makeup of the beans themselves, or the differing roasting methods employed, so it will be as well to suggest that readers should not, after reading this, get too carried away adding this to the list of things to analyse on any coffee that they roast or buy in the future.

    Regardez,
    FC.

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    Re: Dark spots on the roasted beans?

    I would agree woith you all except for the Alien thing, We get them to, both from HG and Popcorn methods, I would tend to go for the fact that they are rapid expansion marks and the blistered section has come off.

    FB

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    Re: Dark spots on the roasted beans?

    In my haste, I suggested that it was a majority of the beans.... the next day when I looked its probably only 15% of them.

    Sounds like it could be any number of reasons, and I tried another roast today (with different beans.... this time Sumatran Lington) and didnt get any pits.

    While different beans are sure to have different roasting qualities, the absence of the pits makes me think it probably wasnt directly a result of my technique (not that Im suggesting I know what Im doing), and Im guessing its a portion of my kenya AA being a little substandard.

    The good thing is the taste. Ive been pleasantly surprised with the flavour..... Ill give the Lington until tomorrow and Ill try it with breakfast.

    Thanks for all of your input, its all greatly appreciated.

    James

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    Mal Dimal's Avatar
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    Re: Dark spots on the roasted beans?

    Hi All,

    From what Ive been able to research these "divots" are caused during the 2nd Crack phase of the roast and is related to the rapid structural failure of the woody or "cellulose" component of the bean. Sometimes these failures (which cause the sound we know as 2nd Crack) occur close to the surface of the bean and so rapidly, that a small particle of the bean is expelled by the forces involved.

    It stands to reason that some varieties of beans will be more prone to the phenomenum than others because of their intrinsic horticultural and varietal differences. Experienced roasters seem to suggest that it can be managed such that it can be kept to a minimum by carefully controlling the heating profile between the end of 1st Crack and through 2nd Crack. Makes sense I guess if you want to reduce the speed at which these stresses build up within the bean.

    In the end, I dont know that it is a terribly bad thing as most long term roasters know about it but arent concerned about any possible negative effects to the final taste. I have noticed them on beans that have been purchased from very noteable Australian roasters and if theyre not worried about them, I dont see why I should be. It might be something worth pursuing if you have access to a particularly good roaster and can readily control the roasting profile, purely from an academic exercise perspective of course. Ill just keep doing mine with a popper until Ive eventually built myself a Turbo-Oven Roaster that allows more control over profiles. That wont be for a while though.

    Cheerio,
    Mal.


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    Re: Dark spots on the roasted beans?

    I definatly had a lot more of these with the Kenya AA than any of the other beans I have tried. The Sulaweise didnt have any at all and the Costa Rica only had a couple for the whole lot.

    I think I got about 15% off the Kenya AA also, and it didnt effect the taste as far as I could tell.

  10. #10
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    Re: Dark spots on the roasted beans?

    re the "divots"

    I used to get these all the time when using a popcorn popper but much less frequently with the heatgun. definitley more likely to occur the deeper you take the roast.

    I use the same setup as you and second crack for me is usually only a couple of minutes after first crack although I cant recall if the kenya was different.

    Its all in the taste though from your description you may wish to try the next batch a bit lighter. Good luck!

  11. #11
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    Re: Dark spots on the roasted beans?

    Sweet...

    I was a little concerned at first that I was the lone ranger on this one, but obviously this is not the case.

    Of course I want my beans too look as good as possible, because it adds to the impressed looks from my coffee loving friends when they see a great looking product....

    Ill try another batch of the Kenya AA this week (Im on leave!! woo hoo) and Ill try slowing down the heat after the first crack (maybe back to the lower heat setting) and see what happens.

    As for my initial roast, Does anyone think that 4-5 mins between 1st and 2nd crack is excessive? did my original roast timings sound off the mark?

    Its all academic really, because I guess when it comes down to it, as Rich said, if it tastes good, who cares what they look like.

  12. #12
    Senior Member fatboy_1999's Avatar
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    Re: Dark spots on the roasted beans?

    Behmor Coffee Roaster
    I used to get the divots more often when I used the popper to roast.
    Not so prevalent with BBQ roaster.
    Quote Originally Posted by Lovebite link=1107601981/0#10 date=1107735912
    ...
    As for my initial roast, Does anyone think that 4-5 mins between 1st and 2nd crack is excessive? did my original roast timings sound off the mark?
    Depends a little on volume and other factors.
    I dont think it is excessive. I usually do 4 cups at a time and the time from the end of 1st crack to the very start of 2nd crack can be anywhere between 2 and 6 minutes.

    As you say, the taste is the important thing. When we get to be exceptional roasters ;) perhaps then we can start to worry about getting the roast time 100% uniform and under controlled lab conditions.

    Now I REALLY want a coffee. Unfortunately, Im at work and I am out of my stuff. Bummer!



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