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Thread: Pump pressure - extraction rate

  1. #1
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    Pump pressure - extraction rate

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Ive been thinking the pump pressure on my San Marino CK was too high. To get a 60ml shot (from the double) in 25 seconds, I have had to adjust the grind down finer than I use on the Silvia. Then the shot seems burnt and over extracted.
    So I unscrewed the spout on the PF and attached a pressure gauge. The pressure built up smoothly to 6.5 bar over about 6-8 seconds, then held steady. Much lower than I had expected.
    Is this too low? And if so, and I increase it, wont I then have to grind even finer?
    I then put the gauge on the Silvia as a comparison, and she pumped upto 10.5 bar over about 5 seconds.
    So can someone explain to me why it is that if the grind and tamp are the same, I get a faster extraction from the CK with 6.5 bar, compared to the Silvia at 10.5 bar. The only other differences between the 2 (as far as I can see) is that the Silvia does take about 2-3mm more in the basket. Is this enough to make the difference?
    The other variable is the jet size. I pulled out the jet on the CK and it is tiny. I measured it at about 0.8mm. I have read somewhere that this is about right.

    Any help and advice gratefully accepted.

    Cafeoholic.

  2. #2
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    Re: Pump pressure - extraction rate

    Hi Cafeoholic...

    6.5 bar is definately too low - it should be 8.5 to 9 bar. Also what is the temp of the group at extraction - if not at about 93C that can cause the flavour to deteriorate..... You might need a cooling flush to remove the overhot water etc... or even a flush to heat the group (dont know the CK myself)

    2-3 mm in the basket can make quite a difference. Is there a slight imprint of the showerscreen in the puck after extraction? Reduced depth of coffee- easier water flow- faster extraction = poor taste!

    I find my standard (14g) La Cimbali basket takes about 19g when correctly filled and tamped so there is just the slightest imprint on the puck.

  3. #3
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    Re: Pump pressure - extraction rate

    So it sounds like I need to increase the pump pressure on my San Marino CK compact.
    Anyone got any ideas on how I do that?

    I havent measured the temperature of the group, but my impression is its good. When I flush water through it, I never get a burst of steam first, like I do on the Silvia. Although I do through the hot water arm. So hopefully you can see where I have drawn my conclusions from, but I will measure it once its back together again.
    At the moment shes waiting on new gaskets, jet, filter and shower screen from Coffee Parts.

    When I dose the basket (I alway use the double, never the single) I put as much in as possible, while still being able to lock it in. There is always an imprint in the puck, and it comes out firm with no puddling on top.
    Ive got an 18g basket on order, Ill see how that changes the brew.

    At the moment Im using the Silvia for my fix, but hopefully not far of getting the CK back into action.

  4. #4
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    Re: Pump pressure - extraction rate

    Ive had interesting results moving between my weekday ecm (bigger silvia) botticelli and the bezzera 2 gp.
    The Bezzera needs a long cooling flush until the water coming out no long sizzles, but I do the same with the botticelli- let the boiler cycle go till the heater stops then flush in the same way.

    Both are adjusted to about 9 bars (actually the bott to 8.5). The botticelli can get close to the bezzera in terms of sweetness and smoothness, but not quite. At least lets say not consistently. Even with similar brew temps and pressure the bott needs one notch finer on the grinder irrespective of adjustments for blend or atmospheric conditions. Part of this I put down to the fact that the bezzera has a very low shower screen which I can allow for by using a ring dofferent on the markings around the pullman tamper.
    You may need to look at dosing because the silvia is the opposite- it has the low shower screen (not sure about san marco though)
    so I partly agree with Gonzo about not comparing but there should be similarities in that both should give fat rich coffee. It will always take some adjustment going from one machine to another. My monday coffees are always a little risky- I tell myself I should run a 30ml single before I make the coffee to check, but rarely do. I guess one other factor is that your baskets will be diff- doesnt a san marco have 53mm and silvia has 58? At least I can standardise on baskets, although the bott is fussier in this department.

    Brett

  5. #5
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    Re: Pump pressure - extraction rate

    Thanks for your reply Telemaster.

    Firstly, The CK does have a 58mm basket. Infact the baskets are interchangeable between the Silvia and the CK.

    When you talk about a lower shower screen, Im wondering which way you mean this. Lower to the ground (and drip tray), or lower in that it doesnt protude from the group so far.
    The Silvia screen doesnt protrude so far, so I can get more coffee in the basket. Probably part of the reason I get a slower extraction.

    I agree with you last statement, at the end of the day, Im just looking for rich and thick coffee, which at the moment, is what Im getting from the Silvia, less so from the CK.


  6. #6
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    Re: Pump pressure - extraction rate

    Quote Originally Posted by cafeoholic link=1165634060/0#5 date=1165743023
    Thanks for your reply Telemaster.

    Firstly, The CK does have a 58mm basket. Infact the baskets are interchangeable between the Silvia and the CK.

    When you talk about a lower shower screen, Im wondering which way you mean this. Lower to the ground (and drip tray), or lower in that it doesnt protude from the group so far.
    The Silvia screen doesnt protrude so far, so I can get more coffee in the basket. Probably part of the reason I get a slower extraction.

    I agree with you last statement, at the end of the day, Im just looking for rich and thick coffee, which at the moment, is what Im getting from the Silvia, less so from the CK.
    In my Bezzera- the commercial, the shower screen protrudes further into the basket, or as you say, closer to the floor. This means that I need to find a way to standardise the amount of coffee I put in it and in the botticelli, which has a higher screen (ie you can fit more coffee in). With my pullman tamper I fill so that when tamped for the botticelli I can see 3 rings on the tamper base and the equivalent of another space (so it looks like 4 rings. On the Bezzera I can just see the 3 rings. Even with this, the Bezzera basket looks more compressed after a pour- maybe why it likes one notch coarser.
    I find yur findings interesting because the bezzera is more consistent and forgiving than the botticelli- the reverse of what you are finding. The bott is basically a slightly bigger silvia but quite similar. The bezzera is a very compact 2 gp with approx 10 l boiler. I used a thermoclouple attachment on my multimeter to check that both run about 91-93 C after flushing and I try to standardise on infusion times too.
    Hope this helps
    Brett
    ps- if anything the lesser pressure of the SM should mean slower extraction, at least relatively- Silvias often run at about 11 bars I think

  7. #7
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    Re: Pump pressure - extraction rate

    Well I got all the Bits from those nice people at "Coffee Parts" yesterday. So Ill put the SM back together again this week, and then get down to some serious trials, see if I cant get her dishing our some glorious crema.
    I also got an 18g basket. Its huge, about 5mm deeper that the Silvia equivilent. I reckon Ill be emptying the knock box every other go.

    Can anyone help me on a how to adjust the pump pressure on a San Marino CK?

  8. #8
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    Behmor Brazen - $249 - Free Freight
    Quote Originally Posted by cafeoholic View Post
    Well I got all the Bits from those nice people at "Coffee Parts" yesterday. So Ill put the SM back together again this week, and then get down to some serious trials, see if I cant get her dishing our some glorious crema.
    I also got an 18g basket. Its huge, about 5mm deeper that the Silvia equivilent. I reckon Ill be emptying the knock box every other go.

    Can anyone help me on a how to adjust the pump pressure on a San Marino CK?
    Hi,

    Find this thread, I have the same problem now! Have a San Marino compact CKX, the gauge point to 0.5 after the machine is ready, I think it should between 1.0 to 1.25, Did you find any soulation?



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