# Pre-infusion on a Gaggia Classic?



## rgoodcoffee

Hi,

I was just curious if its possible to do a pre-infusion on a gaggia classic? Also what advantage really does a pre-infusion give?

thanks!

Rory


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## Inspector

Never thought about this before. I will definitely give this a go on my next shot to see what happens


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## Mrboots2u

Hmm not sure i would see that link delivering true pre infusion ...


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## tommyp215

Based the above video, if you were to turn on the brew button for a second or two and then switch it off you might some residual low pressure leave for 5 seconds and then press full power and extract as normal? Does that logic sound about right?


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## bluebeardmcf

tommyp215 said:


> Based the above video, if you were to turn on the brew button for a second or two and then switch it off you might some residual low pressure leave for 5 seconds and then press full power and extract as normal? Does that logic sound about right?


I think that may work with a non-solenoid model, but I would expect a disaster with a rapid pressure change in a 3-way valve model like the Classic - someone please correct me if that's my mistake.

I think that the use of the steam valve would reduce the amount of pressure to the group head, something I'll experiment with just for the hell of it.


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## mirceat

rgoodcoffee said:


> Hi,
> 
> I was just curious if its possible to do a pre-infusion on a gaggia classic? Also what advantage really does a pre-infusion give?
> 
> thanks!
> 
> Rory


Based on what Bill Crossland said on the above video, we always do pre-infusion on Gaggia Classic.

We should call soft pre-infusion the feature you are interested into. Pre-infusion at lower pressure and/or lower flow-rate than those provided in normal use.

There are manual procedures that apparently help on soft pre-infusion. But attention, the steam knob technique drains more hot water than usually and pulls more cold water from the tank. The water temperature in the boiler could drop dramatically, depending on how much do you turn on the steam knob. Consequently, you should find a way to compensate the temperature loss. The result in the cup is largely dependent on how well the boiler keeps the temperature balance during the shot.

The manual procedures being limited and cumbersome, the logical follow-up is to look at the automatic solutions providing better temperature control and/or pump control. Some internal machine changes might be involved, but the user definitely gets more consistent shots and a larger playground for experiments.


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## hotmetal

tommyp215 said:


> Based the above video, if you were to turn on the brew button for a second or two and then switch it off you might some residual low pressure leave for 5 seconds and then press full power and extract as normal? Does that logic sound about right?


I may be wrong, but when I had a classic it had the Auber PID with PI and steam enhancement. This effectively allowed you to set a timer for the "PI" during which the pump would activate, and then a 'dwell time' before the actual shot per se would commence. So you effectively got something like "Pump for 1 second, wait for 3 seconds, pump for 25 seconds". This isn't 'soft PI' as I understand it, but if the pump runs for only 1 second or something, there isn't time for full pressure to build up at the puck, even though the pump itself is not running at a lower pressure. It basically just sprays a bit of water to pre-wet the puck, allows it a moment to soak in and for the pressure to dissipate in the basket, then begins the extraction, which in any case will take a few seconds before a full 9 bar is seen. I can't say how much better this is than without, because I bought my Classic with the PID already fitted and always used it in that way. I was happy enough with the results. I don't think there is anything to say it's bad for the solenoid, as the Auber kit has been around for a long time and I've not heard anyone say that.

Personally my feeling is that trying to rob the manual PI of its pressure by opening the steam wand would be more likely to have negative consequences for the shot temperature stability which would outweigh the benefits such as they may be of 'softening' the initial pre-wet. That pressure isn't really there until it has had a chance to fully saturate the puck and begin the extraction I believe.

Happy to defer to experts with manometers or engineering qualifications, but the above is how it appeared to me when I had mine.


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## rob177palmer

Steam wand pre-infusion works very well.

Open the steam valve a quarter turn then immediately press brew. I pre-infuse for 5 seconds then close steam valve. Coffee starts pouring at c. 10 seconds.

This gives a low pressure pre-infusion and doesn't crack the puck (clicking brew switch on and off gives a big risk of this).

Studying the pre-infused puck vs non pre-infused, it is clear that the puck swells more with the low pressure wetting....the thought being it helps to offset less-than-perfect distribution.


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## rob177palmer

On the temp stability point, I had a PID. A 30g shot starting temp is 97 degrees for me, the end point measures 91-92 degrees.

The 5 sec steam wan pre-infusion usually releases around 20g water.

To me that seems stable enough and I certainly haven't noticed and souring of the shot.

Pre-infusion seems to have helped me producing reliable shots.


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## mcrmfc

You might want to search for the Mrshades dimmer mod detailed on the forum from a couple of years back, if you have the invensys pump this can give you something closer to genuine pre-infusion.


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## les24preludes

Just pulling up this thread to see if there are any worthwhile updates and clever things you can do with a Classic.

I tried the 5 second quarter turn on the steam wand at start of the shot, and the taste was good in the cup. Would have to do more meaningful comparisons but certainly seems worth looking into and experimenting with.


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## AndyZap

I've done the MrShades' mod for controlling the pump (Invensys pump + dimmer + pressure gauge) and I think this is definitely worth it.

Apparently there is a simpler option (see posts from GrahamS in this thread https://coffeeforums.co.uk/showthread.php?20575-Gaggia-Dimmer-Switch-low-pressure-pour&p=598451#post598451 ) - which should work with any dimmer and Ulka pump. You can add the dimmer first (which does not look too complicated) and see if you like it, then add the pressure gauge later.


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## foboundy

So... having finally got around to heavily modding my Gaggia Classic, I'm at the point of wondering about pre-infusion...

So far I have:

- Installed my own Arduino-based PID, based heavily on the work of others here: (http://int03.co.uk/blog/project-coffee-espiresso-machine/) and here: (http://tomblog.firstsolo.net/index.php/hobbies/pimping-my-coffee-machine/)

- I've also installed both manual and digital pressure gauges as per the above though mine is installed on the boiler itself using a bodged Evo steam valve to gain access to the pressure in the boiler rather than the HP side of the UKLA pump

- I also have a flowmeter on the LP side of the UKLA with the OPV outlet tee-d in to correctly allow for the OPV bypass volume

So far, so good but what is clear from the above is that a substantial volume of water is used to saturate the puck in the pre-infusion phase. Looking at the output by eye, I estimated 15 - 25 ml for a typical double shot so when the flowmeter reads, say 60 ml, you've only got ~40 ml in your cup. How then to properly account for this?

I decided that the only way to properly measure when coffee hit the cup was to install a load cell under the drip tray. This wasn't a simple task as it required a re-design of the drip tray (3D printing solved this one!). I finally got all of this working today and I think the results are interesting.

The chart below shows a pretty good shot. The flowmeter starts clocking up volume straight away but the load cell (uncalibrated) stays flat for about 4 seconds while 28 ml of water saturates the puck. During this period pressure gradually ramps up to 9.2 bar. After 21 seconds I have a shot with a net (in the cup) volume of 63 ml.

Back to pre-infusion. I'm guessing that the objective here would be to lower the pressure during the pre-flow phase but to what value? I have the necessary hardware to control my UKLA using a zero-crossing triac but I guess I am questioning whether it is worth the hassle of mucking around with 240v.

Any thoughts, comments or advice more than welcome. At some point I will post a full write-up pf my mods but at present it's still Work In Progress...


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## shodjoe1

I'm tried already twice,no difference on my side.Same taste,which is still good :*)


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## naio

I've been playing around with the steam knob "hack" and after around a week of experimenting I noticed that I get the best results with the following technique:

1. Warm up the machine for around 10 mins or more (obvious step







)

2. Open/turn the steam knob around 110° degrees and let any built up steam escape

3. Turn on the brew switch and start closing the steam knob slowly for about 6-7 secs

4. Enjoy









P.S. It might be my imagination but my tastebuds can taste a difference


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## AndyZap

Scott Rao' post https://www.scottrao.com/blog/2018/7/18/advanced-mode-on-the-de1 inspired me to try repeating this with Gaggia Baby. My dimmer switch can be switched off completely, so I can do pre-infusion with the pump off. Also Scott Rao used paper filters to boost the extraction (this was also mentioned by @Colio07), so I decided to get Whatman filters to use under the pack and aeropress filters about the pack. The beans are Rocko Mountain by @foundrycoffeeroasters.com

I recorded the weight per sec in the cap (from Acaia scales) and pressure from T549i bluetooth pressure sensor. The red curve is the standard shot, no paper filters. I use this for FW (the dimmer does not go all the way up, so the pressure drops naturally similar to a lever machine). This one is really nice in FW, but not very interesting in americano for this beans. The blue curve is my attempt to replicate DE1. This one is with the paper filters and finer grind. I do the pre-infusion at the lower dimmer setting (this gives about 3 mL/s flow), then switch the pump off for 30 sec. Then rump the pressure to about 7 bar. What can I say? ... the best americano I ever had, so much flavour. And I do not usually drink americano, but with such a nice one it is easy to convert .


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