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  • Degassing, light and dark roasts.

    Effect of Roasting Conditions on Carbon Dioxide Degassing Behavior in Coffee

    As an observation.

    Over my years of roasting I've noticed that darker roasts tend to degass at a much faster rate than lighter.

    I have tended to stop all of my roasts over the last couple of years at the first few snaps of SC or 225° whichever happens first, these roasts degass at quite a slow rate, in fact over a few days the bag barely inflates.

    Yesterday by way of a change decided to roast 750 grams of Yirg 10 seconds past SC, all went to plan, yep the beans were decidedly darker than usual, so, into a one way valve bag, expelled as much air a possible before sealing it, 2 hours later the bag had inflated considerably and by this morning had almost reached balloon proportions.

    Wonder if others have experienced this?

    This short article was all I could come up with after a brief search on Google.

    Xiuju Wang, Loong-Tak Lim



    Department of Food Science, University of Guelph, Guelph, On, N1G 2W1, Canada
    Food Research International 01/2014;
    ABSTRACT CO2 is one of the major gases formed during coffee roasting, which has important implications on coffee’s quality and packaging requirements. In this study, the residual CO2 content and CO2 degassing behavior of an Arabica coffee processed using a fluidized bed roaster, as affected by the roasting temperature-time conditions, were investigated. The results showed that positive correlations existed between the degree of roast (expressed as lightness value) and residual CO2, implying that lightness could be used as an indicator of initial CO2 content in roasted coffee. At the same degree of roast, coffee roasted with high-temperature-short-time process had significantly higher CO2 degassing rate than those with low-temperature-long-time process. Moreover, the CO2 releasing rate increased with the degree of roast. The degassing rate of CO2 in ground coffee was highly dependent on the grind size and roasting temperature, but less dependent on the degree of roast. The different degassing behaviors observed between roasted coffee samples were explained on the basis of chemical composition and microstructural differences.




  • #2
    Hi Yelta
    The findings in that article seem to match what I've experienced - with the same degree of roast (i.e. drop point temp) if I roast faster to get there, there is more degassing required (i.e. the exploding portafilter and puffy bag!) but when I roast with my now standard longer, gentler profiles, there is very little resting required - I can drink straight out of the roaster. The bags will still swell a little once opened… so I wonder if this is a reaction to oxidation in my beans?

    I think your findings make sense too - if you roast darker than normal, you'll start 'pushing' everything out more quickly (think oilsetc ) so maybe CO2 would follow suit in this process?

    Cheers Matt

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    • #3
      Morning Matt.

      Your statement "if you roast darker than normal, you'll start 'pushing' everything out more quickly (think oilsetc )" seems to be correct re oil, my normal roasts show no signs of oil at completion, however, that extra 10 seconds or so will certainly get them sweating a bit.

      Comment


      • #4
        Yeah, same here. Don't think I've ever taken anything to 'oily sheen' land

        The most I tend to go is just into 2C by about 30secs - and even then there is usually little oil. Especially when you can remove sourness & acidity if need be by roasting a little longer leading up to 1C - why add bitterness at the end!

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        • #5
          You know over the years I have allowed myself to be influenced by the lighter roast brigade (anything past CS8 is charcoal- blah blah blah) and have lightened my roasts off accordingly.

          I have always been a lover of darker roasts, well last nights exercise was a revelation, pulled a shot with the Yirg this PM, what can I say, the pour flowed like molasses, a thing of beauty, and the flavours! a combination of intense chocolate with citrus overtones, I thought lighter roasts were meant to bring out the citrus notes, regardless, the exercise has been an unqualified success, very pleased with the outcome.

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          • #6
            I did a similar batch of Yirg a few weeks ago and got very similar results … yum! Rich caramel choc over citrus.
            But I've also got some lighter roast yirg that I did for the Aeropress/plunger in the hopper at the moment - which is a true citrus explosion! No choc - but a lovely drop anyway. Almost choked the machine with it this morning - got about 25ml from a triple basket after about 2minutes - and it was sensational!

            Comment


            • #7
              Originally posted by Yelta View Post
              You know over the years I have allowed myself to be influenced by the lighter roast brigade (anything past CS8 is charcoal- blah blah blah) and have lightened my roasts off accordingly.

              I have always been a lover of darker roasts, well last nights exercise was a revelation, pulled a shot with the Yirg this PM, what can I say, the pour flowed like molasses, a thing of beauty, and the flavours! a combination of intense chocolate with citrus overtones, I thought lighter roasts were meant to bring out the citrus notes, regardless, the exercise has been an unqualified success, very pleased with the outcome.
              I echo the sentiment. In general I do roast into the first few snaps of second and have been stretching the roasts a few more snaps into second (for espresso) and this is where in general I have found my taste buds to like. Having said that however, it also depends greatly on the beans. One example is the Monsoon M arabica which I just couldn't understand why it tasted burnt every roast. Then we go into the whole soft beans hard beans characteristics but particularly on the MM with the monsooning process I have to keep reminding myself to ignore the visual and trust the other senses. A lower charge temp and pretty much after finish of rolling 1st (maybe a few seconds past) is where I have found the MM will avoid being burnt.

              So long story short, yes I like darker roasts in most cases but it also depends on the beans...and brewing method (but that's another story).

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