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Question regarding preinfusion

I've had my R since fall of 2017. Since then I have enjoyed the machines ability to make excellent coffee.

My machine is one of those who had the pressure switch changed out determining preinfussion pressure.

To date I have found coffee to fit the machines properties rather than adjusting the machine to fit the coffee.

I was expecting to do the latter and my question/comment is regarding if that can be done.

I would like to "tune" the preinfusion to fit a coffee from a local roaster. It seems to require a higher temp and possibly a gentler preinfusion. I'm basing this off of an older L1 running at 1.1 bar and line pressure preinfusion. This is a expresso result that I can't equal. I have access to both machines.

To the point, is the mater pressure switch not adjustable like the first variant and if not can another be substituted that would allow this to happen?



  • hi john

    a great question, thanks for posting

    the original L1(2012-16) was at its best for darker roasts, with pre-infusion occurring at boiler pressure, which in your case sounds like it was 1.1 bar

    the LR ships at a setting that is best for lighter roasts, with a pre-infusion pressure of 3.5 bar set at the switch to give about 3.0 bar at the puck. this elevated pre-infusion pressure also produces much higher brew temperatures

    a darker roast extracts more easily than a lighter roast, so a smaller dose is generally used with less pressure and the attendant lower brew water temperatures

    if you have access to the original L1 and prefer the taste of a given roast on that machine to the LR it is presumably a darker roast and you need to turn down the pressure setting on the Mater pressure switch. the Mater has a pressure range from 1.5-4.0 bar so you will be looking to dial the Mater down to the bottom of its operating range

    you will notice that it has a splash of white paint on the adjustment screw to discourage meddling; this is because Mater supply us with the switches pre-set to a pressure of our choosing, in this case 3.5 bar. with the machine disconnected from the electrical supply use a needle or similar to carefully pick out the white paint from the gap around the adjustment screw. there are arrows on the adjustment screw indicating which direction to turn the screw to either increase or decrease the pressure

    we are currently developing a more sophisticated mechanism that we will make available as an upgrade kit that is easy to retro fit to the LR, so this may be of interest to you

    kind regards

  • Reiss,

    I've removed the white sealant. I've moved the screw towards the negative, thinking I'd have a negative stop, I kept going but it's obvious there is no negative stop as the screw became too loose.

    Is there a recommendation in turns from fully in to get a specific pre infusion setting.

    This is great, thanks for the help.

  • Hi John

    I would turn the pressure down on the Mater until the lever grabs at 45 degrees above horizontal, just like the original L1 you have access to. You don’t need any instruments with this approach

    You will of course need to grind more coarsely and tamp more gently or preinfusion will not complete in a reasonable period of time

    It will then perform in an identical manner to the original L1, giving you the best of both worlds


  • Bingo,

    The adjustment was easy. I turned down the pre- infusion pressure until I essentially got a dipper (no pump). The lever caught just above 45deg.

    I slowly dialed the setting until both the pump engaged and the lever caught at 45. First coffee required a bit more heat. Moved boiler to 1.1 bar.

    Now it's coming in. Worked on grind. I'm close on this bean now.

    The ability to tune the machine to the bean is wonderful. I'm getting more steam as a bonus. Doesnt matter normally but occasionally I steam a larger pitcher when pulling a number of shots for a group of people. Here the extra steam is welcome.

    I am interested in the mod you mentioned. Repeatability of adjustment is my desire (via a gauge if possibility) and the ability to make changes without popping the top cover.

    Appreciate your assistance

    Bob (John Robert McCarthy)
  • on our current range of machines please dont change the boiler pressure from the factory setting of element off at 1.0 bar - this is a general message to everyone, otherwise you will end up in a world of pain

    the original L1(2012-16) is a completely different architecture and generally needs to run at a pressure greater than 1.0 bar

    if you need more heat for the coffee you are using on the LR just tweak the pre-infusion pressure up slightly so the lever grabs slightly lower than wherever you currently have it grabbing

    if you want to steam barrels of milk get the larger 4 hole tip, i think its 1.4mm x 4 from memory


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