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Disappearing crema - diagnose this!

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  • Disappearing crema - diagnose this!

    Hi all,

    Weve recently changed coffee suppliers at the cafe I work at, and some new toys have come with the package.

    The machine is a La Scala Carmen 3-group (brand new), and the grinder is a Santos 55 (Automatic). The automatic grinder means that the dose is identical (or close to), which is great because the consistency between staff before was abysmal!

    However, weve noticed since the change that our crema recedes to a darker, thinner amount during the time it takes to steam milk. The appearance of the crema directly after the shot is normal (great, even!). Here are some clues:
    - We were using the same (new) beans on the old machine (Expobar 3-group) and didnt have this problem.
    - The shots are almost ideal (havent finished tuning grinder and volumetrics yet) with ~50mL in 20-25sec for a double. While Im hoping to slow this down a little more, this shouldnt be too fast, right? And would that produced disappearing crema anyway?
    - Dose level is ideal, IMO. Any more and the PF feels tight when plugged in.
    - Tried some beans that got delivered today (as opposed to those that were delivered last week) and there was no difference (having said that, they could be the same batch).

    Things I havent tried (yet):
    - Using the spare grinder (Mazzer SJ) to see if the Santos is the problem (it is awfully fast, dosing a double in under 2 seconds!).
    - Using some coffee that I know to be super fresh (ie. my home roasted stuff) - Id be very disappointed if our new supplier (or the roaster) was giving us stale beans, but its possible).
    - Checking the temperature settings of the boiler (could be burning the coffee?).

    Any diagnoses are appreciated!

  • #2
    Re: Disappearing crema - diagnose this!

    It seems to me that you have your experimenting and problem-solving well sorted.

    In my (very limited) experience with disappearing crema it is usually stale beans.

    How does the coffee taste? Thats the ultimate test.

    Ill be interested to hear what the experiments show.



    • #3
      Re: Disappearing crema - diagnose this!


      Could be the grinder Stuart.... It appears to be a 2-Pole motor driving ~64mm burr-plates at around 2,850 RPM. That is really fast and I wouldnt be surprised if this is having some effect on the beans. Youll know for sure though if you compare it with the Mazzer. An interesting concept, this grinder... :-?



      • #4
        Re: Disappearing crema - diagnose this!

        Thanks guys,

        Greg - youre right; I need to do more empirical research (ie. tasting)...

        Mal - I did find that info and was alarmed by the 2,800 rpm figure... but Im loath to learn anything negative about the grinder because the auto-dosing feature comprises such an improvement in our coffee (potentially, at least).

        Ill do some testing tomorrow if I get the time. Trying the Mazzer should be easy enough. Our "coffee guy" (the rep for the new coffee supplier) is coming some time this week so we might be able to test the brew temp. [Forgot to mention, by the way, that the brew pressure is good (AFAIK) - starting at 9 bar and edging up to 10 bar during the first 10 secs of the shot.]



        • #5
          Re: Disappearing crema - diagnose this!

          Hi all,

          just an update.

          So, I thought the problem could be either:
          1 - grinder burning beans
          2 - head pressure too high
          3 - stale beans
          4 - head temp too high

          I ruled out the grinder by using the Mazzer SJ and getting the same result. The machine has a head pressure guage which shows good numbers while brewing so thats not the problem (assuming its accurate-ish). The beans smell pretty good - not gassy and not stale - so its not that. Which leaves us with brew temp. Once Id figured that out, I started noticing things I hadnt before - eg. the heads need flushing to get rid of steam/water even after only leaving for a couple of minutes. I also remembered that dark crema can be caused by too hot an extraction temp.

          Soo, Im fairly sure our machine is running hot. I mentioned that it could be too high a temp to our coffee rep (before Id convinced myself that it was), and he said something about "dont have much control over that" - I wasnt quick or assertive enough to say "why the hell wouldnt you be able to set whatever boiler temp you desire?!!!" (maybe next time) - and that he wasnt keen make any changes while the boss was on holidays (which is until a week from today), which is fair enough, I guess.

          As it stands, Ive been flushing the heads A LOT before every shot and it seems to be okay. It does mean that were having to empty the drip tray bucket 3-4 times a day instead of once!

          Will update when we have some success.