For those who have one, how is preinfusion accomplished? Is it needed?

The GS3 has a solenoid that interrupts the pump for a programmable amount of time. That is, pump goes on... pause 1... solenoid closes... pause 2... solenoid reopens. You can set the length of pause 1 and pause 2. From One week with the La Marzocco GS3:

HB wrote:As Ken and Jim documented in How to Preinfuse; Extraction Pressure Redux, there is arguably a benefit to preinfusion under mains pressure ("At 3 bar, good stuff is happening, the water has enough pressure to go through the whole puck in a reasonable time."). That's not an option for espresso machines drawing water from a reservoir, but the GS3 does provide start-stop-start preinfusion by closing / reopening the grouphead solenoid in the early seconds of the extraction.

Lino stopped by this evening to help plot the GS3's pressure profile resulting from this design:


The "speed bump" is the on/off pulse

The thread Pressure profiles, preinfusion and the forgiveness factor shows the pressure profiles of several other espresso machines. This profile resembles the Elektra A3's no preinfusion design, except for the small speed bump and a less inclined rise, presumably thanks to the GS3's smaller diameter gicleur. Lino and I were surprised to see that the group depressurizes and repressurizes after the preinfusion cycle. I programmed in one second of pressurization followed by two seconds of dwell time. While I haven't tried it yet, I assume that allowing much longer would mean a higher rise and fall, which could disrupt the puck's adhesion. Given the GS3's already easy nature, I wonder if it would improve further still with a higher pressurization to 3 bar and no depressurization as How to Preinfuse advocates?

You can hear the solenoid close and reopen in this video:

I've been using pre infusion regularly now. Mainly for the forgiveness factor, but I wonder if it really is being any more forgiving. I have a LM naked portafilter that should arrive today or tomorrow. I do plan to see how it effects extraction over time. Perhaps there's less chance of channeling or whatever with the short preinfusion.

Basically, although the preinfusion doesn't show much of a difference in the pressure profile, except that little bump. Nevertheless, there is a small amount of water which ejects onto the puck and presoaks the top of the puck . This may or may not help when the puck is coming up to full pressure.

I was told by Tim at Pacific Espresso that La Marzocco has done research on the pre-infusion and they couldn't find any taste difference.

You might also notice that the default is "off" for pre-infusion.

Despite these facts, I still turned it on because psychologically I somehow think it will still help cover me in the case that I make a mistake in distribution, tamp, whatever.

On the other hand, it does mess with the chronos when you consider that the real brew time does not start at 0 seconds. So when you have the chronos function on and pre-infusion, and you are looking at the timer, you have to figure in that there's approximately 3 seconds of pre-infusion time (I have mine set at .9 seconds on / 2.4 seconds off for a double).

I think that it would be helpful to clarify some terminology here. Frankly, I have no idea what preinfusion technically means, or, indeed, if there is a settled definition. It would be nice if someone could comment on that. I use it to refer to anything that basically slows the initial flow rate down and I think that I'm not alone in that. Preinfusion in this sense can be accomplished via a gicleur, which basically does nothing more than just a narrowing of the tube carrying the brew water. (Correct me if I'm wrong!) Gicleurs can be installed in La Marzocco machines and I'm pretty sure that they come standard on all machines now (at least in Australia). Common sizes are 0.6mm and 0.8mm; there might be a 1mm gicleur as well. The smaller the diameter, the longer time it takes to see the first drops of espresso. If you are thinking about e61s when you are thinking about preinfusion, it might interest you to know that e61s also have a gicleur in the group to do precisely the same thing. Then there's the pump on/off thing that everyone has already discussed.

I'll leave the merits of "preinfusion" - however it is defined - to another post.

Cheers,

Luca

I think that it would be helpful to clarify some terminology here

I'm not sure the proper term, but because my machines have adjustable settings I call the first part "soak"(lower pressure regulated), then the second part where the traditional gicleur is used, I call it ramp. I guess both parts to some would be preinfusion.

Perhaps it's better to group everything that happens with brew water, prior to the main infusion as pre-infusion.

The ramp-up seems like a way to provide a short amount of preinfusion immediately coupled with the full pressure infusion.

The La Marzocco's pre-infusion setting provides for even more control over this pre-infusion by allowing for custom setting of pre-infusion that can be changed according to the user's desire. On the other hand, the pre-infusion of a gliceur is short, pretermined albeit has it's own desirable quality of it's own. Also, consider the properties of the gliceur are duplicated during the custom pre-infusion phase because the gliceur is a physical part of the machine that cannot be turned on or off.

Now those are difference between methods, but what are the differences with the results! I'm not quite sure about that. According to La Marzocco research, there is no benefit. I've yet to discover for myself. I've had it on for a while and things are going good. Next, I need to turn it off and see if things get worse or better.

Perhaps what happens is I end up adjusting my extraction technique, temperature, grind, etc, to match the results I'm getting. So either way, I end up getting to the same results.

It's "pump-pulse" pre-infusion.
The pump goes on for a programmable amount of time, then shuts off for a programmable amount of time, then goes on again.
The idea is to "pre-saturate" the coffee before beginning extraction.
This is not the "gentle pre-infusion" that you would get from some other techniques (line-pressure pre-infusion or gravity pre-infusion for example).

The topic of "is pre-infusion valuable and effective" is a complicated one.
Before beginning it, however, it is important to differentiate the topic as there are four embedded topics here.
1 - Is pre-infusion at a concept level valuable and positive.
2 - Is pump-pulse pre-infusion valuable and positive at an experiential level.
3 - Is line pressure pre-infusion valuable and positive at an experiential level.
4 - Is pump-pulse or line pressure "better".


Restriction via jet/gicleur is not "pre-infusion" but rather a change to the profile (water debt, pressure ramp).

Some machines like the LM GS2 with its paddle group let you pre-infuse the puck with water at a lower pressure than the 9bar the pump makes. It allowed water at supply line pressure to saturate the puck before the pump was turned on.

I am not sure if the GS3 is hooked up to the water suppy, if it will work the same way without the pump running during pre-infusion.

houdina wrote:Some machines like the LM GS2 with its paddle group let you pre-infuse the puck with water at a lower pressure than the 9bar the pump makes. It allowed water at supply line pressure to saturate the puck before the pump was turned on.

Line-pressure pre-infusion.

Pre-infusion on a machine with heavy flow restriction (like the 0.6mm restrictors on the GS/3) is redundant.

Stick with the pre-infusion set off.