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Thread: Gaggia Classic temperature study

  1. #1
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    Gaggia Classic temperature study

    Cafelat Coffee Tamper and Accessories

    For anyone whos interested, Ive just finished temperature logging my Classic with a thermocouple probe inside the filter basket. The results I obtained shocked me. Virtually irrespective of flow rate (ie singles or doubles) the temperature falls by nearly 10 C during a shot. I have logged 10 different runs of the machine and all results show and immediate and rapid temperature drop during brewing operation. Ill be posting a complete report with all the data to alt.coffee if youre interested.

    Bottom line: The Classic does not provide a stable brew temperature, so upgrading to a HX or even a Silvia shoud offer an improvement in shot quality.

    BTW: What I have found is in stark contrast to the oft quoted Norwegian study, but Ill let the data speak for itself.

  2. #2
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    Re: Gaggia Classic temperature study

    Mmm.

    I am a bit surprised. I certainly got good results from my Gaggia Classic when I had it.

    It sounds like you have started the long, tortuous and expensive journery to espresso enlightenment.

    Do yourself a favour, either shoot yourself now or just get the La Cimbali Junior DT1 now and be done with it.

    He he he.

    If you did the same exercise with any machine you would probably find quite a bit of variation.

    I would like more information on how you measured this. You would need to measure the incoming water using a vary sensitive and rapidly responding thermocouple.

    Regards,
    Grant

  3. #3
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    Re: Gaggia Classic temperature study

    Ive posted a full report on alt.coffee

    I used a k-type thermocouple with a small 1 mm bead junction. The bead was placed in the porta-filter between the grounds and the shower screen. I also ran a group head measurement and saw the same effect albeit reduced by the thermal response of the metal.

    Here are the graphs I made with the data. Temp was logged at 0.4 sec intervals and read directly to a computer. a 120 second measurement window was used.

    Why did I do this? Im a scientist and we do things like this. ;)You also have to bare in mind that this is my machine and I would have loved to paint a glossy picture of it. But this does also go some way to explaining why it is difficult to remove the sour notes from the espresso (once Ive dropped below the bitter threshold with the PID controller).

    BTW: I plan on fixing this machine.






  4. #4
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    Re: Gaggia Classic temperature study

    Well done!

    Im not sure how the Silvia would stack up. I have heard that a temperature variation of 5 degrees during the shot is normal for the Slivia but i havent seen anything definitive. It has a similar design but a boiler more than twice the size of the Classic and more thermal mass in the brass so the variation would be considerably less.

    Espresso Nirvana though can be expensive to achieve.

    I will be interested to see how you go with other machines.

    Regards,
    Grant

  5. #5
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    Re: Gaggia Classic temperature study

    Very nicely done Sparky! Me ats off to you! :D :D

    Id love to do a similiar study of my Cimbali. :)

    Java "Loves to experiment" phile

  6. #6
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    Re: Gaggia Classic temperature study

    This is the reference to the original 2001 study on the Silvia by Greg Scace.

    The temperature variation is indeed only 1 - 2 degrees fahrenheith with the Silvia during shots.

    Remarkable really and a good reason to get one!

    Grant

    http://groups-beta.google.com/group/alt.coffee/msg/fb66109cb119634c

  7. #7
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    Re: Gaggia Classic temperature study

    Ill be tinkering with my Classic for a while yet. First Ill get the PID thermocouple close to the
    boiler/group junction to better sense the load and compensate. Ultimately I plan to buy and butcher
    a Sunbeam Ristretto and use its boiler as a pre-heater for the Classic. That should cure its thermal ills.
    Otherwise, wed have to hold off on painting the house so I can get me a Zaffiro ;D

    Yes, finally (for me at least) the debate over the Classic vs Silvia is over. Silvia hands down.

  8. #8
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    Re: Gaggia Classic temperature study

    Not really...depends on the application.

    I for one am always uncomfortable when *specifications* for espresso machines
    are being discussed.

    May I suggest the only test worthy of note, is the one where you make the
    coffee, and you decided whether you liked it or whether it was well produced or
    not / OR / the one where you have kindly been loaned the use of a mates silvia,
    and you run both in parallel with same coffee etc to see how the espresso from
    each compares over a series of say, no more than 4 coffees at a time ( 2 straight
    after 2) given the size & capacity of these domestic machines.

    We also dont know whether that which has been measured is quite normal for the
    Gaggia or whether there is something wrong with the individual machine. If not and
    the temp variation measured is normal for it, what does it mean ( particularly if there
    is nothing wrong with the coffee produced)?

    Heat Exchanger machines vary quite a bit too, *even from group to group on the
    same machine*, and that is the nature of the beast.

    We have to be careful with the possibility that we could be reading too much into
    these things.

    Coming from left field as usual.

    Regardz,
    FC.

  9. #9
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    Re: Gaggia Classic temperature study

    Let me first be clear that I am not saying that the Classic is incabable of making good coffee.
    I drink coffee at home that is nicer than 95% of those served in coffeeshops. In fact I made a
    cappuccino for my neighbour and he rated it at a 9.7 and was adamant that coffee couldnt get
    better than that. I rated it highly as well. But then I also rated the coffee that my old Sunbeam
    thermoblock machine was producing very highly. First and foremost get good fresh beans. Then get
    a good grinder. Learn to tamp consistently, then worry about your machine.

    As for my machine, the only thing that I can think of that could adversely affect the performance that
    much is if the transfer pipe inside the boiler, that takes the brew water from the top of the boiler, is missing.
    The only way to know if my machine is defective is to remove the boiler and have a look. Of course it may be.

    To test whether it is possible to actively compensate for the large thermal load, I ran a series of shots with
    the heating element switched full on. Ive just posted the results to alt.coffee. The graph is here:

    http://i4.photobucket.com/albums/y129/mjfernee/Classic/Brewtemperature_elementon.jpg

    It shows that the heating element is incapable of compensating for the huge initial thermal load.
    So active control of the brew temperature is out.

    If it is my machine that is defective, Id really like to get it fixed.

    As for the taste, Id been tasting espressos from a few coffeeshops known for their espressos, and found a strange uniformity to their shots. In contrast I find that I am incapable of removing the slight sourness with my PID controller, even though just 0.5 C change can remove any bitterness. Its hard to describe, as I havent been trained to describe complex tastes, but there is a substantial difference. However, as soon as you add milk, all the ills disappear.

    If theres any other Classic owners in Brisbane that would like their machines "tested", its entirely painless to the machine and only stale beans are harmed, just let me know.

    Cheers,

    Mark.

  10. #10
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    Re: Gaggia Classic temperature study

    It is possible that the transfer pipe could be broken off but that usually
    only happens when it is disturbed (as in when someone is servicing the boiler).

    Good idea to see if others Classics do as yours does. Do you know
    if there is a Gaggia service agent in Brisbane?

    Regardz,
    FC.

  11. #11
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    Re: Gaggia Classic temperature study

    In the intersts of scientific repeatability, Im more than happy to slip my thermocouple
    into someone elses basket. Maybe the guys at Barazi would allow me to test their demo Classic?

    BTW: Im not saying that Classics are incapable of making good coffee. Just that they seem to be thermally unstable.
    One of the consequences of this is that a modification to PID control of the Classic will be far less effective than
    a similar modification on a Silvia or similarly designed machine.

    The reason that the Classic is thermally unstable is probably as folloows: The group is actively cooled by the feed water during the brewing process.

    Im pretty keen to compare other machines now, as well as confirm the Gaggia result. This sort of techy info is pretty scarce on the web. Id ideally like to compare a Classic and Silvia side by side. The shot to shot comparisons as well.


  12. #12
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    Re: Gaggia Classic temperature study

    For all those who are still interested. Jack at Barazi (one of this sites sponsors) very kindly
    let me have access to a Bezzera BZ99 to test my data logging gear and methods. So I dipped
    my thermocouple into the BZ99s basket in exactly the same manner as I used for my Classic.

    You can find the BZ99 result here (showing two successive shots with no prior cooling flush):
    http://i4.photobucket.com/albums/y129/mjfernee/Classic/BZ99_a_b.jpg

    For the sake of comparison, Ive also made a graph that directly compares my Classic to the BZ99.
    http://i4.photobucket.com/albums/y129/mjfernee/Classic/Gag_v_Bez.jpg

    For those wondering how a heat exchanger machine should operate, go to this site
    and have a read.
    http://www.home-barista.com/hx-love.html

    You see temperature profiles for other HX machines there to compare with my results for the BZ99.

    Illl post more results for different machines when they come in.

    In the mean time I should say that after visiting Barazi and seeing a current Classic boiler in the
    flesh, so to speak, Im a little underwhelmed. There is far less metal in it than I originally suspected.
    They also had an older Gaggia boiler that is nearly 3 times the weight (metal volume). So there may be
    some considerable differences in how these older machines perform.

    Again thanks to Barazi for helping me out. Id highly recommend them to anyone looking for
    coffee equipment in Brisbane.



  13. #13
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    Re: Gaggia Classic temperature study

    Cafelat Naked Group Handle
    Hi all, sorry for digging this one from the grave, just dont want to duplicate thread topics :p

    I recently purchased a thermo coupled thermometer for my Gaggia Classic as it has slowly been degrading over the last 6months and i wanted to check the operating temps. The shots are not quite as good as what they used to be, and its harder to steam (Silvia mod done ;))

    Anywhoo, i placed the thermometer on the side of the boiler (as far up as i could). My temp read outs are about 82 deg water and 104 for steam. I find this a little odd because i only recently replaced the boiler and a thermostat (steam) about 1yr ago. The machine is just over 3years old now, service frequently.

    Im not overly fussed though... because i am taking deliver of an Isomac Venus shortly, ordered it last Monday night (before the euro fell a little), should be arriving Monday morning (currently over the pacific ocean on its way to botany), cant wait! Will be looking at installing the Silvia PID within the next 6 months. First i want to do some operating temp test. Will post them up (if they havent already)

    Back to the Gaggic classic, any suggestions what i could do! I am going to give it away, want to make sure its not a total dud.

    Cheers
    Peter

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