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Overextraction.... um... what is it?

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  • #16
    Re: Overextraction.... um... what is it?

    Originally posted by mean bean link=1170933141/0#10 date=1170980815

    I stand by what i said about overextraction. But you are right also. Its all to do with how much of the oils are extracted by the flow of hot water. Too fine a grind or too heavy tamping will choke the flow and cause it to leech too much of the oils out of the grounds by the time it gets through the puck. Overextracted and bitter. So in this scenario, overextraction is in process even before the coffee starts to drip out of the PF.
    But I can now see what you were saying, JavaB, about the extra-long pour also leading to overextraction. I wonder, is it due to different oils (more bitter in taste) being extracted, or a difference in surface oil and oil deep within the grounds (if there can be deep within a coffee ground!) or a difference in what happens to the flavour of the oil if exposed to boiling hot water for too long (gets burned)?
    Likewise, in my scenario above, do you agree that it leeches too much of the oils or do you think it is that the oils get burned by the hot water not flowing and thereby spending more time (and presumably applying more heat) to the puck and its trapped oils?
    mean bean.....

    A sort of non technical explanation (which works for me)...

    Remember the sugar coated nasty tasting pills you give to children.....

    Well if you swallow them fairly quickly - before the sugar coating is dissolved- they leave a sweet taste in your mouth...... extract the flavour for too long - by sucking on the sweet coating and then yuck!!!

    Chew the tablet up so it is smaller..... and the nasty taste starts sooner....... and if the pill is too large to swallow.... you have to chew it first.....

    The more technical explanation goes into the volatility of the various oils, the temperature which these oils are extracted, their depth below the surface of the coffee grain etc......

    Even correctly extracted coffee has different components during an ideal 30 ml shot..... Next time you make an espresso.... collect it into 3 shot glasses - 10 ml in each.

    Taste the first 10 ml...... rich smooth and sweet
    2nd 10 ml.... not as rich or as smooth and the sweetness will be a lot lower.
    3rd 10 ml... starting to get bitter and unpleasant... no smoothness left...

    Combined together they taste fine..... but continue extraction and the quality gets less and less causing the overall taste to rapidly deteriorate.....

    The 30 ml volume is a good compromise..... you could just extract 10 ml which would be wonderful..... but you would require a lot more coffee (plus some people actually like a little of the bitter taste).

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    • #17
      Re: Overextraction.... um... what is it?

      Originally posted by Kaffee Schnüffler link=1170933141/0#11 date=1170983339
      ....
      My brain is also a tad scientific, and I have found a few articles over time that explain what actually gives coffee its taste:

      http://cosmicvariance.com/2006/08/07...ence-of-coffee
      ...
      The article by Illy linked from the above that Kaffe gave is a fantastic read. In there he goes into quite a bit of technical detail about what makes up the shot and the differences in under/over extraction.

      Great for people like me that like to understand such things at a deeper level 8-)

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      • #18
        Re: Overextraction.... um... what is it?

        Originally posted by JavaB link=1170933141/0#8 date=1170972253
        Kind of a glass half empty / glass half full discussion
        Everyone keeps forgetting the third option........the glass is the wrong size.

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        • #19
          Re: Overextraction.... um... what is it?

          Hi All,

          And heres a link to an explanation about the finer points of coffee extraction, in a practical sense, from Home Barista. The relevant info is found towards the latter half of the page,

          Cheers,
          Mal.

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          • #20
            Re: Overextraction.... um... what is it?

            Originally posted by meg-e link=1170933141/0#14 date=1170999548
            Im sure you had other things to do - I appreciate it!  
            I dont know what gave u that strange idea. Other things to do?!!
            Are u kidding!! Were Coffee Snobs. What else is there in life besides talking coffee?!! ;D

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            • #21
              Re: Overextraction.... um... what is it?

              Originally posted by mean bean link=1170933141/15#19 date=1171065799
              Originally posted by meg-e link=1170933141/0#14 date=1170999548
              Im sure you had other things to do - I appreciate it!
              I dont know what gave u that strange idea. Other things to do?!!
              Are u kidding!! Were Coffee Snobs. What else is there in life besides talking coffee?!! ;D

              Exactly! Since a certain event in my life, it comes to pass that some of my local friends are finding out what I do with some of my spare time! Any way, some were having a chuckle at the fact that there is a whole forum dedicated to all things coffee! Like, their point being "Its only a cup of coffee!". I started to rattle off the different forums we have for discussing coffee and their mouths dropped open in amazement. When I got to the part about roasting at home that really floored them! LOL!

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              • #22
                Re: Overextraction.... um... what is it?

                Meg-e as a presso user myself, grind size, good tamping and pre-heating the presso and group head have been the three biggies for me. I always pull the shot early too.

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                • #23
                  Re: Overextraction.... um... what is it?

                  JavaB, your explanation is great. I would just summarise by saying that, if your temperature and pressure are correct, then other factors can cause local overextraction at the surface of the coffee grain, but global underextraction of the puck. This is why I would say that even early blonding is usually over - not under - extraction, as you said. It is interesting, is it not, that coffee snobs can still have lots to discuss about even the most basic of (coffee) lifes questions?

                  Originally posted by JavaB link=1170933141/15#15 date=1171000974
                  Even correctly extracted coffee has different components during an ideal 30 ml shot..... Next time you make an espresso.... collect it into 3 shot glasses - 10 ml in each.

                  Taste the first 10 ml...... rich smooth and sweet
                  2nd 10 ml.... not as rich or as smooth and the sweetness will be a lot lower.
                  3rd 10 ml... starting to get bitter and unpleasant... no smoothness left...

                  Combined together they taste fine..... but continue extraction and the quality gets less and less causing the overall taste to rapidly deteriorate.....
                  Yes, but that would assume that you only want a rich, smooth, sweet taste in your cup - a bit two dimensional, isnt it? You know, if you let the pour go for a few seconds into the blond, you can add a few high notes to the flavour which are not at all unpleasant. It is all about balance; too much of the smooth, and it is a little dull. Too much of the harsh, and it is undrinkable. A balance of different tastes produces a well-rounded cup, much like a balanced wine, with the right proportion of tannins, acids, sugars and fruits. At least, this is what I prefer. This is perhaps why true doubles are harder to pour, and harder to appreciate, but in the end are more complex and satisfying.

                  I think you have made it much easier for Meg-e and others to understand this very important concept.

                  Matt

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                  • #24
                    Re: Overextraction.... um... what is it?

                    Originally posted by grendel link=1170933141/15#21 date=1171102158
                    Meg-e as a presso user myself, grind size, good tamping and pre-heating the presso and group head have been the three biggies for me. I always pull the shot early too.
                    thanks Grendel

                    Does pulling the shot early mean not letting the puck get too wet before pushing the arms down? or does it mean cutting the shot short after it starts pouring?

                    That is... I hold the arms up for 10 seconds after pouring the water in before I pump the arms. Do you do this for less time? and I wait until Ive squeezed the last drop of water out of the machine (Ive been doing a double pump as thats what I saw Cam do).

                    Im playing around with grind size at the moment (variable numero uno). I would have thought it is best to start coarser and gradually go finer or is it the other way around?

                    I practiced tamping on the bathroom scales much to the amusement of significant other. Cant seem to do 14kg (is that right?). So *Sigh*... now I just HAVE to get a Pullman Tamper!  ;D

                    Thanks again everyone for the discussion

                    Meg

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