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Thread: When do I need to prime? (Gaggia Classic)

  1. #1
    Senior Member Dragunov21's Avatar
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    When do I need to prime? (Gaggia Classic)

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    This may [s]seem like[/s] be a stupid question, but I only just came across the concept of priming the boiler using the steam wand.

    I've been trying desperately to troubleshoot my shots, which range from sour to grapefruit-juice with the occasional delicious smooth nutty example. With fresh, well-roasted coffee (5 Senses TwentyFourSeven), an OPV set to 135psi and a Baratza Preciso dialed in for 25g pulls in 30 seconds, I'm still getting shots that are merely "drinkable" as caps/lattes.

    I've also found that after the first shot, unless I use the steam switch to manually boost temp (which results in the next shot starting at ~98°C at the shower-screen if I leave it long enough and 92-89°C if I don't, quickly falling) I have to wait 15+ minutes until the grouphead returns to temp, and it still falls faster than I'd expect and produces a sour shot.

    Now I read that it's necessary to prime the boiler and I feel a bit silly thinking that the sour shots result from pulling a shot from a half-full boiler that's quickly flooded with cold water...

    So do I prime through the steam wand after every shot/PF-purge cycle, then get it to temp and repeat, or do I pull the shot, purge the PF, get it back to temp, THEN prime it?

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    You only need to prime a single boiler after steaming, and you should do so immediately after steaming.

    Your sour shots may result from the temperature being off, but usually lowering temperature tempers sourness (IIRC in any case), 98 is probably too hot though, best extraction is supposed to happen around 92-94.

    The problem with the Gaggia classic is that it has a fairly thin stainless boiler which makes it less temperature stable than say the heavy brass boiler in the Silvia, *might* be worth looking at insulating your boiler.

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    Quote Originally Posted by jbrewster View Post

    The problem with the Gaggia classic is that it has a fairly thin stainless boiler which makes it less temperature stable than say the heavy brass boiler in the Silvia, *might* be worth looking at insulating your boiler.
    This is incorrect.
    The Classic actually has a fairly thick Aluminium boiler with a brass group assembly.

    To the OP, the standard classic needs to sit for at least 6 mins undisturbed prior to pulling a shot, no flushing, priming ect.
    Due to the nature of how the thermostat behaves this is where its peak thermal stability lies.

    Best time to start to pull a shot (after the machine has been sitting for at least 6 mins) is just as the ready light comes on.
    This way there will still be latent heat from the element during your shot.
    If you wait any longer that heat will transfer into water and group resulting in to high a start temp (flashing steam from shower screen) leading to burnt and possibly at the same time sour tasting shot.

    Yes you should only prime through the steam arm after steaming. If you flush all that water through the group you loose what little temp stability it has.

    All these problems are drastically reduced and virtually eliminated by installing a PID on the classic. It really makes it a completely different machine to use.

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    Senior Member Dragunov21's Avatar
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    Just waiting on some M4 brass standoffs to mount the TC, then I'll be good to go with a PID...

    I should also prime when I first power-on the machine from cold, yes?

    Thanks so much for the explanation; makes complete sense and now I understand what's happening in there a bit better. Still going to try and hook up a thermoblock preheat to allow pouring shot after shot though...

    I just pulled two shots as per above and they were great; still gotta play with the grind/dose a bit but having sorted the temp variable will make everything a lot easier, I think.

    I'm kicking myself for not realising it though; I went through about half a pound of coffee last night pouring shot after awful shot, getting more and more pissed as the shots got sourer and sourer despite getting better and better flows >.<

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    Quote Originally Posted by Dragunov21 View Post
    Just waiting on some M4 brass standoffs to mount the TC, then I'll be good to go with a PID...

    I should also prime when I first power-on the machine from cold, yes?

    Thanks so much for the explanation; makes complete sense and now I understand what's happening in there a bit better. Still going to try and hook up a thermoblock preheat to allow pouring shot after shot though...

    I just pulled two shots as per above and they were great; still gotta play with the grind/dose a bit but having sorted the temp variable will make everything a lot easier, I think.

    I'm kicking myself for not realising it though; I went through about half a pound of coffee last night pouring shot after awful shot, getting more and more pissed as the shots got sourer and sourer despite getting better and better flows >.<
    No worries

    Yes i always hit the brew switch when first turning on, just until it flows freely from the group. Good practice for all single boiler machines.

    Patience is the key with the lower end machines. However PID speeds things up heaps, enough for my use.
    If you get that pre heat working properly you will have very temp stable machine, up there with units that could cost $1000 plus.

    I have toyed with the idea of using some annealed copper refrigeration pipe wrapped around the boiler. My attempts at finding the suitable connections locally were not good. All in all i am pretty happy with the machine as is. Its rare that i need to pump out more than a couple of coffees at a time.
    Anyway i just try convert people to drinking piccolos...

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    Quote Originally Posted by Steve82 View Post
    This is incorrect.
    The Classic actually has a fairly thick Aluminium boiler with a brass group assembly.
    Couldn't remember 100% if it was Stainless or Aluminium. IIRC Aluminium is more thermally conductive than most brasses so it'll lose heat faster in any case. The practical upshot is that it'll also heat up quicker.

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    Quote Originally Posted by Dragunov21 View Post
    I should also prime when I first power-on the machine from cold, yes?
    Still going to try and hook up a thermoblock preheat to allow pouring shot after shot though...
    I prime as part of my warmup routine now.

    I don't think you need thermoblock preheat if you have PID; a 1000W element can boil a shot's worth of water from room temperature in 8 seconds (ie if you have your element full-on during the shot, the temperature will go up intrashot).

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    Senior Member Dragunov21's Avatar
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    The thing is that I'm not sure on the transport lag the way the thermocouple's installed. I'll have to see how much the group temp fluctuates during continuous use then make a determination on whether to preheat or not.

    IIRC, people were still seeing significant intra-shot ΔT after installing a PID; it merely allowed them to control initial temp to a finer degree and at exactly the same temp each time without surfing?

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    What is a PID?

    Quote Originally Posted by Steve82 View Post
    This is incorrect.
    The Classic actually has a fairly thick Aluminium boiler with a brass group assembly.

    To the OP, the standard classic needs to sit for at least 6 mins undisturbed prior to pulling a shot, no flushing, priming ect.
    Due to the nature of how the thermostat behaves this is where its peak thermal stability lies.

    Best time to start to pull a shot (after the machine has been sitting for at least 6 mins) is just as the ready light comes on.
    This way there will still be latent heat from the element during your shot.
    If you wait any longer that heat will transfer into water and group resulting in to high a start temp (flashing steam from shower screen) leading to burnt and possibly at the same time sour tasting shot.

    Yes you should only prime through the steam arm after steaming. If you flush all that water through the group you loose what little temp stability it has.

    All these problems are drastically reduced and virtually eliminated by installing a PID on the classic. It really makes it a completely different machine to use.
    Sorry for possibly a dumb question, but what is this PID ehat you speak of?

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    try google

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    Senior Member deegee's Avatar
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    Quote Originally Posted by usnelsons View Post
    Sorry for possibly a dumb question, but what is this PID ehat you speak of?
    Put very simply, it is a super-accurate thermostat replacement.

    Gaggia thermostats are set to a fixed temperature, and will allow fluctuations of up to six or seven degrees above and below nominal.

    A PID is adjustable and will hold to much closer tolerances. They also have a digital readout.
    They usually have to switch the boiler power via a relay as their contacts can't handle the current.

    They will try to keep the temp steady during a shot, but it will drop as the cold water enters the boiler.

    P.I.D. .JPGClassic with PID .jpg

    Here are pics of a PID and a Gaggia Classic with a PID fitted.



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