# Gaggia Classic slow extraction



## j33v3s (Nov 1, 2014)

Hi all

First post - but have been here plenty before doing research into various things. Apologies for the long post!

Bit of Background:

So I've been enjoying learning about coffee for a number of years now. I got my current espresso machine (Gaggia Classic) probably about 3 years ago.

Grinder: iberital IC2

Mods wise:

Pretty much out of the box - removed the "pressurised" basket and "magic crema" thing, and replaced with a standard basket. Also swapped out the "magic" froth wand for a silvia one.

Have just fitted an auber PID kit, and had probably just over a week of faultless performance before my issue cropped up.

During fault finding, adjusted the OPV to ~ 10bar using a pressure gauge on the bottom of my (pre filled with water, but nothing else) portafilter. Found it was over 14bar (max reading on guage) before.

Now the issue:

I get very very slow extraction when trying to pull a shot of espresso. After the 25 seconds the PID has the pump on for (this is with factory setting pre-infusion, 0.9 second pump, 1.2 second soak), I only JUST start to see espresso drip out of the spout.

Fault finding:


Ran a full tank of descale through, also backflushed with descaling powder as well. While I was running the descaler through, I alternated between group head with no portafilter, group head with blind (blind basket) portafilter & steam wand for release of liquid.


When doing backflushing/using blind portafilter, still get the "normal" (eyeballed quantity) volume of fluid coming out of the release tube into the drip tray.


I have checked that the OPV valve is totally unobstructed (dismantled the entire valve) - no scale or anything and all parts are in top notch condition.


Checked that the solenoid actuated valve is clear and no bits of anything trapped in the small holes.


Checked that water flows from the group head, and through the steam wand with no "load" (i.e. no portafilter or milk for steaming etc).


Checked that with a blind portafilter in (this was the portafilter with a pressure gauge on the bottom) I got about 60ml in 15 seconds from the OPV return. All the while, the gauge read a steady 10bar.


Checked that, once the boiler was heated to steaming temp (around 150 C with the PID), when opening the steam valve and turning on the pump, I still get a similar flow rate to what I got before (totally unscientific measurement here, just a case of "yeah that looks about right").

I have not changed the beans/grind during this time - about half way through a 1kg batch of beans. I did try last thing last night dialing back the grind a bit, but no change.

So, any ideas? All the evidence points to no individual part being at fault. Yet when pulling a shot, something is clearly wrong. I'm pretty stuck really!


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## froggystyle (Oct 30, 2013)

You sure you only lowered to 10bar, maybe worth seeing if you can pick up a another gauge to test, might be faulty?

Other than that i have no idea, sorry.


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## gingerneil (Aug 21, 2014)

Have you tried with a very coarse grind and a light tamp ? It should fly through and taste disgusting, but it would show that the Gaggia is able to pump the water through the group with at least some resistance. If this works, slowing pull the grinder back to where you would expect and see how you go. Could be grinder has been knocked/adjusted so its grinding superfine ?


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## NJD1977 (Dec 16, 2014)

All I can think of (which are very obvious points so I'm sure you've already checked):

1. Is the basket clear and clean - i.e. are all the holes properly unobstructed etc.

2. Is the shower screen clean and clear - have you taken it out and given it a good clean?

3. Have you tried some other beans?

4. Have you altered your tamp in any way?

5. Does the Auber PID have any sort of pressure dimming control, and if so, is it the Auber that's dimming the pressure when it shouldn't be?


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## j33v3s (Nov 1, 2014)

Thanks for the suggestions so far

To answer questions:

@ NJF1977

1. Yes, that gets cleaned every time I pull a shot

2. Yes, this has been removed and cleaned, along with the dispersion plate as well. All cleaned and no scale/other gunk present

3. Yes, unfortunately I first noticed the issue when I got a nice (christmas gift, as these things are expensive!) bean subscription through the post. First shot was with those beans. First thing I did was switch back to my normal bag for testing.

4. Not altered my tamp in any conscious way

5. Not as far as I am aware. The features advertised essentially only control temperature and pump duration. I will double check the spec later though.

@gingerneil

I haven't tried this, no. It's unlikely the adjuster got knocked, on the iberital it's a step-less worm drive adjustment, and very stiff. Also my eyeball and finger tools both give similar results (i.e. looks similar, and when pressed between finger and thumb it leaves a slight impression of my fingerprint without clumping, which in my research seems to be about right?) Although as I've eliminated so many other things I will definitely check this tonight.

@froggystyle

It's unlikely pressure is the issue. I first noticed the issue before I'd done the pressure change - so it was at factory stock. I'd been planning to do a preheat coil, thus replacing the factory OPV with another positioned before the preheat coil so was holding off changing it. I only changed it half way through the fault finding as I wanted to check the internals of the OPV. However, you're right that the guage *could* be misreading. It's unfortunately not something I can really afford to buy another just to check. And since it was reading just over the gauge's 14 bar max before, and 270 counter clockwise adjustment on the OPV got me to about 11 bar (as per a lot of other people's experience) I'm fairly confident it's at least in the right ballpark.


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## Mrboots2u (May 10, 2013)

Are you dosing the exact same weight of beans each time ? I may have missed it but I can't see reference to a weighted dose in your first post. If there apologies and ignore me


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## j33v3s (Nov 1, 2014)

@Mrboots2u

No, I don't weigh my dose. I fill the (double) basket level to the top of the basket before a gentle tap and then tamping.

I did try weighing once, but it was a bit too much faff and I don't think I can convince my wife to let me buy a set of scales just for coffee (the PID was a push!)


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## jeebsy (May 5, 2013)

j33v3s said:


> @Mrboots2u
> 
> No, I don't weigh my dose. I fill the (double) basket level to the top of the basket before a gentle tap and then tamping.
> 
> I did try weighing once, but it was a bit too much faff and I don't think I can convince my wife to let me buy a set of scales just for coffee (the PID was a push!)


Scales cost about a fiver off eBay and will improve your coffee vastly


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## Mrboots2u (May 10, 2013)

j33v3s said:


> @Mrboots2u
> 
> No, I don't weigh my dose. I fill the (double) basket level to the top of the basket before a gentle tap and then tamping.
> 
> I did try weighing once, but it was a bit too much faff and I don't think I can convince my wife to let me buy a set of scales just for coffee (the PID was a push!)


i suspect you have been over dosing then

as you change coffees and grind size the amount in weight you are putting in the pf is changing , even though it looks them same by eyeball....( i.e. you are levelling it off )

a difference in 16g to 18 g can be chocking the machine ...( slow extraction )

Id try getting a consistent dose by weight before you do anything else....and dialling in accordingly before you do anyhting else....

Re scales and phaff up to you but you are in a place where the coffee isnt good ,

This is one way of removing one variable that may be at play ( the amount of coffee your using )

for the sake of a minute or so - to weigh the basket with ground the coffee in and taking some out , to get at least dialled in and consistent amounts worth it ( IMHO )

The first point of call for a slow extraction ( before looking at the equipment malfunction ) is how much coffee you are using and at what grind size ...then adjust one and only one , while keeping the other the same to see if it improves flow rate and taste . To do this is is helpful to have some £5 scales ( either to make sure your dose is the same and change the grind or to change dose amount while you change the grind the same )


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## MartinB (May 8, 2011)

One thing to try is to see how much water is dispensed in one minute.

Anything around 600mls in a minute is fine.

Place a measuring jug under the grouphead and time one minute.


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## El carajillo (Mar 16, 2013)

I would agree with" Boots" ,I think your problem is with grind or dose quantity. When you have tamped, try placing a 1 p coin on the puck then lock into brew head. Remove and check for mark /depression, If marked you are over filling.

One other"possibility" for slow flow would be a particle of scale in solenoid valve partially restricting the flow. ( But I think the grind /dose most likely)


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## j33v3s (Nov 1, 2014)

I'll get the scales out tonight and see what happens. If it does fix the issue, might be worth rigging up a weight sensor on my grinder. I'm often doing more than one drink at a time, normally 2, but 3 or 4 can be common. So doing this sort of "fine tuning" will add a lot of time.

It's odd that this is happening with two types of bean, and has never happened before in the whole time of owning the machine (and using the same method of dosing). And to confirm, the beans in my "main" packet at the moment have worked using this method.

Will feed back what I get.

@MartinB

I have tried testing the water output from the OPV "release" pipe when under load and that seems ok (was ~60ml in 15 seconds - and maintained the same reading on the pressure gauge the whole time).

I'm assuming when you say 600ml you mean coming from the group head under no load? In which case, not massively time consuming, so I will definitely give that a check as well.


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## MartinB (May 8, 2011)

j33v3s said:


> @MartinB
> 
> I have tried testing the water output from the OPV "release" pipe when under load and that seems ok (was ~60ml in 15 seconds - and maintained the same reading on the pressure gauge the whole time).
> 
> I'm assuming when you say 600ml you mean coming from the group head under no load? In which case, not massively time consuming, so I will definitely give that a check as well.


Yes


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## Mrboots2u (May 10, 2013)

j33v3s said:


> I'll get the scales out tonight and see what happens. If it does fix the issue, might be worth rigging up a weight sensor on my grinder. I'm often doing more than one drink at a time, normally 2, but 3 or 4 can be common. So doing this sort of "fine tuning" will add a lot of time.
> 
> It's odd that this is happening with two types of bean, and has never happened before in the whole time of owning the machine (and using the same method of dosing). And to confirm, the beans in my "main" packet at the moment have worked using this method.
> 
> ...


It might not solve the proble it or be the root of the problem... but

Getting the scales out and dialling dose and grind back in will rule it out as a cause though, and then lets us move on to other ideas and suggestions...

Let us know how you get on and good luck

Cheers


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## j33v3s (Nov 1, 2014)

Ok, will have to eat my doubts. Having adjusted the grind down a fair bit, and ensuring I used 18g of coffee each time (producing 2oz) I started to get flow (too fast - the PID is set to 25 seconds after the pre-infusion which is what I was getting roughly before - 5 seconds before liquid comes out, then 20 seconds to pull the shot)

I then dialed up slowly until I got 2oz of espresso in the 25 seconds.

The shot left a very, very slight bitterness on my tongue after letting some roll around my tongue.

I will have to play with the grind slightly I think there, but for now I'm just happy to have it working again (I tend to drink latte most which means I can get away with slight imperfections in the espresso).

I must have knocked the grinder at some point, because I can't believe it was all down to over-dosing (which has worked for me for years, literally).

On the plus side, I'm now very confident of the internals of my machine, having been in and out loads over the past week, and nothing is physically broken.

Incidentally:

No, the PID does nothing to the pump pressure. I do want to get a dimmer in there and have a bit of a play though. Back to the modding









Thanks for input all.


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