This post has been in the making since I bought my Gaggia Espresso and MDF combination in late 2004. The first thing I have to report is that both have been rock solid for my all these years. They have both been used daily. The MDF suffered a broken star cog that turns the doser just last year. That was a blessing in disguise because I found that it is much nicer to turn the doser from above with your finger. The MDF also has been modified to operate without steps and was also modified to gain easy access to the grind chute so I have zero grind retention and can grind per dose. Two excellent mods. Other than a couple of burr changes and group gaskets, maintenance has consisted of keeping things clean. A very durable and low cost package. Now to the real reason for this post. I must admit that I have struggled with the combo over the years. Getting the right temperature was my first hurdle. There is a lot of info out there on that and it just takes time, patience and coffee to figure it out. I have used a naked portafilter for years and it has been a great and frustrating tool. I felt that I could control all the variables pretty well but the one huge issue that I could never solve is the channeling and spritzing I got on every shot. I'm not talking about an errant spritz every now and again, I'm talking about near disaster every time. I have gone through every distribution and tamping trick out there. Every one! I up dosed and under dosed. Still I never could get a clean pour. The shots were always OK about half the time but the cup always looked like hell and of course tasted bad half the time. I always figured that the real problem was that the pump just put out too much pressure. The puck just could not handle getting hit with that much pressure. I never measured how much pressure the machine applied but I know that without an OPV, the pump unrestrained, put out too much. I know there are mods for this but I figured that money could be put to use for an upgrade someday and I really just wanted to master the machine as it was. I told myself I would never upgrade until I figured this machine out. I started to work with some preinfusion techniques to soften the blow to the puck. These met with very limited success. Th best is to crack the steam valve before you start the pump and then slowly close it to start the extraction. The real breakthrough came when I decided to leave the steam valve open just enough to bleed off some pressure during the whole extraction. The very first time I did this I got the best extraction that I have been able to get from this machine in the last nine years! Not one spritz. Perfect shot time and volume and great taste. It was a miracle to see the clean even extraction and the clean cup. It was so simple and it's so easy to do that I feel a bit foolish for not thinking of it sooner. I'm sure that this information is out there somewhere and if it is I sure wish I had found it sooner. I have been doing it this way for a couple of days now and it is wonderfully repeatable. Like the post title says, slow learner, but I guess the point is stick with it!
If you block the PF then output is the flow from the safety valve and your wand. That can be "calibrated" against the pressure vs flow chart similar to doing a blind OPV adjust on a machine with adjustable OPV. You would have to supply tank water through a small container and use a second container to measure safety valve output and combine that with steam wand output. 9 bar pressure is about 65 ml total out in about 15 seconds. I do not know how the safety valves like a blind PF, or for how long, though you would drop the pressure enough to have most output through the wand. Also you can search AndyPanda and pressure profiling and see how he used varied pressure on Gaggia.
I have the same machine. I had mine for quite a few years, but it was just put in the garage after a while. I got back into espresso again for the past few months. I started getting my beans from a local roaster which when the end of the day comes, they taste just like my roasts. Zero in on the grind as the beans aged in a week was the challenge for me, once were I knew that would go, then the tamper sorted out. I get some nice shots, then every once in a while its either way too long with a dribble, or a 10 second shot. Anyways what I do is 60 seconds before I pull a shot, I run the pump thru the PF remove and load with the grinds, pull the shot, when its done I open the steam wand to get rid of the back pressure and not have the grounds spray across the counter when the PF is removed. My pucks are very well intact. The next step will be a new machine and sorting out which way to go. I now I'm back to roasting my own bens for espresso and enjoying it.
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