How to dial in pre-infusion

February 14th, 2022, 1:09 am

Hi I just added the dimmer mod and gauge to my gaggia. Now I understand how pre-infusion allows you to grind finer. Should I still aim for 25-30 second for a 2:1 shot once I get to full pressure? What is a common rythem for a pre-infused pull? Something like 2 bar for 10 seconds and 9 bar for 25-30?

I put it all in a maple and beech enclosure. I still need to work on the fit and get a fancier dimmer knob. I love the feel of the toggle switch.

#2: Post by **Jeff** » February 14th, 2022, 7:13 am

It's sort of the other way around. For lighter roasts, it can be challenging to extract well. A finer grind can help, but puck integrity starts to be an issue, even with great prep. A soak before ramping up the pressure gives you more options on grind that don't choke the machine or end up channeling a the water bores holes through the weaker parts. I generally find medium-dark roasts and many medium roasts (most things labeled as for espresso) tend to be overly bitter for my tastes if I use extended soak. I find most medium-light and light roasts (almost never labeled as for espresso) can be better balanced between acidity and sweetness with a finer grind and enough soak time to get the puck evenly saturated.

February 14th, 2022, 8:59 am

Welcome to HB Nick

I use a scale to measure extraction, a naked portafilter to analyze the shot real time, a shot mirror for easier viewing and a stop watch with lap timer for the various stages of the shot. I go from line level preinfusion to pump based on what I see on the bottom of the portafilter through the shot mirror and from pump back to a line pressure 'post infusion' towards the end of the shot, all based of experience and intuition. The shot is stopped based on a 2 to 1 ratio of extraction verses ground coffee and the stop watch data is used as reference info for grinder adjustment of fineness and weight.

Your dimmer mod and pressure box looks like it can double as a Chess Clock.

Nice job!

#4: Post by **BaristaBob** » February 14th, 2022, 9:18 am

Just as points of reference I'm enjoying two coffees right now.

The light roast
19g in / 38 - 40g out
20s preinfusion at 3g/s water debit until first drops
another 35s at 9 bars declining to 6 bars until targeted amount in cup.
Temp. 205F

The medium roast
19g in / 34-36g out
10s preinfusion until first drops
another 20s at 9 bars until target amount in cup
200F

#5: Post by **GDM528** » February 14th, 2022, 10:12 pm

Speaking of Gaggia Classics and preinfusion...

I replaced my brew switch with a dual toggle so I can operate the pump independently from the pressure-relief valve:

This allows me to briefly turn the pump on and off (about 2ish seconds) to load a fixed amount of water and pressure into the basket - then just let it soak its way through the puck. I wait until I see the water reach the bottom of the basket before pulling the shot, typically 10-30 seconds. I read various approaches, some of which run over a minute for preinfusion, at which point it doesn't make sense to subtract that from the overall budget. Can't say that I've ever noted any taste differences that I could attribute solely to the preinfusion time, so I don't include in my shot timing. I quit pulling shots just based on time - instead I stop based on color, and adjust grind if it runs notably over/under 30 seconds.