Results 1 to 10 of 10
Like Tree6Likes
  • 1 Post By Dimal
  • 1 Post By flynnaus
  • 1 Post By ermat
  • 2 Post By Lyrebird
  • 1 Post By ermat

Thread: Giotto v2 brew pressure

  1. #1
    Junior Member
    Join Date
    Apr 2019
    Location
    NZ
    Posts
    29

    Giotto v2 brew pressure

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    I have read various ideal brew pressures. Mine is measuring 8.5 bar on a pressure gauge fitted to the bottom of a spare portafilla. What do you guys think, is it low ? Is it ok ? Should i leave it or should i adjust it ?

  2. #2
    Mal Dimal's Avatar
    Join Date
    Oct 2004
    Location
    Warwick, QLD
    Posts
    16,960
    How's the coffee taste?

    Mal.
    flynnaus likes this.

  3. #3
    Senior Member flynnaus's Avatar
    Join Date
    May 2008
    Location
    Sydney
    Posts
    4,114
    Mal's right. Provided your technique is right, if the coffee is good in the cup then that's all that matters. Don't rely on your pressure gauge reading other than for troubleshooting faults eg no or very low pressure.

    Brew pressure is a balance between temperature and boiler pressure which needs to be adjusted according to your preference and best left to a professional technician with the right equipment. Coffee machines bought from reputable dealers are usually calibrated before delivery to the buyer using a device which tracks temperature and pressure throughout the brew cycle. Once adjusted your machine shouldn't need adjusting again.
    Dimal likes this.

  4. #4
    Junior Member
    Join Date
    Apr 2019
    Location
    NZ
    Posts
    29
    It is no trouble for me to adjust it. Just wondering what the optimum pressure is for this machine.

  5. #5
    Mal Dimal's Avatar
    Join Date
    Oct 2004
    Location
    Warwick, QLD
    Posts
    16,960
    8.5 to 9.0 Bar is perfect...

    Mal.

  6. #6
    Junior Member
    Join Date
    Apr 2019
    Location
    NZ
    Posts
    29
    Quote Originally Posted by Dimal View Post
    8.5 to 9.0 Bar is perfect...

    Mal.
    Thanks Dimal.

    Just out of interest, if I was to increase the pressure to say 9.5 bar, would that mean that a finer grind would be required to lower the greater water volume in the given 25- 30 seconds due to the heigher pressure ?
    And if that was the case, would there be a discernable difference in the cup between the two settings ? I thought I read somewhere that a finer grind as the potential to improve flavours ?
    I am happy with whats currently in the cup at 8.5, I'm just interested in the science behind the brewing options.
    Dimal likes this.

  7. #7
    Senior Member Lyrebird's Avatar
    Join Date
    Jun 2018
    Posts
    568
    Yes to the first, Darcy's law applies so flow rate is proportional to pressure for a given permeability and viscosity. Grind, dose and tamping all affect the permeability of the puck which also changes with wetting and during extraction. The CO2 level and extract have the biggest effects on viscosity. Wetting, extraction and CO2 level all change with time during the shot so the flow rate also changes.

    The second is more complex. All else being equal, the finer grind (smaller average particle size) at similar flow rates should increase extraction as the surface area to volume ratio increases as the inverse three halves power of the particle dimension. The complication here is that the increase in level of highly soluble things like organic acids will be smaller than for less soluble things like chlorogenic acids for the simple reason that most of the former would already be dissolved.

    Only you can tell whether the increased extraction improves the resultant coffee for you. For me increasing extraction tastes better until it doesn't.
    Last edited by Lyrebird; 14th June 2019 at 05:47 PM.
    Dimal and LauriG like this.

  8. #8
    Junior Member
    Join Date
    Apr 2019
    Location
    NZ
    Posts
    29
    For me increasing extraction tastes better until it doesn't.

    Thanks Lyrebird, like you say, I won't know until I try.

  9. #9
    Junior Member
    Join Date
    Apr 2019
    Location
    NZ
    Posts
    29
    Made the adjustment last night. 1.5 turns in on the opv moved my pressure on the portafilla gauge from 8.5 bar to 10. That should be around 9bar actual. (The blind portafilla reading is typically 1 bar higher than actual head pressure)
    I have plenty of finer adjustment remaining on my grinder so will take make it a notch or 2 finer and see how it goes.

  10. #10
    Junior Member
    Join Date
    Apr 2019
    Location
    NZ
    Posts
    29
    Noticeably more interesting result from 9 bar/ finer grind. Now looking forward to delving into home roasting. Have recently picked up a used Behmor.
    Dimal likes this.



Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •