La Pavoni Europiccola and Fellini/multi pump physics? - Page 2

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LObin

#11: Post by LObin »

I'm still trying to understand the reasoning behind the "Fellini only adds to the yield when the puck is not fully saturated"...

The puck absorbs water. Some more water is used to extract a few drops of coffee that have fallen inside the cup. If you raise the lever again, you'll replace some of the freed up room between the puck and the piston, with more water. Yes, there's air trapped above the water but there's still more water entering the group (you can actually hear it) and therefore, more volume of water in that column that can be pushed through the puck. Maybe one would get more consistency by doing a "half Fellini" only when the puck is not fully saturated, it's quite possible. Haven't really thought about comparing between saturated vs pre-saturated "half Fellini's".

Whether it's more harmful or not, that's for everyone to figure out. As I mentioned before, like many others, I was having mixed results with the "half Fellini" untill I added a puck screen.
LMWDP #592

jackdaddy

#12: Post by jackdaddy replying to LObin »

Good point for me to try to elaborate on. Let's assume the puck has absorbed enough water to become saturated and maybe even some drips out. Let's also assume the lever is still in the fully raised position. Under these conditions, any water lost to the puck or cup is being constantly replaced by water from the boiler as long as the lever remains up due to boiler pressure. So any freed up room in this scenario is already being replaced with pressurized water. If the puck isn't fully saturated, pulling the lever down increases water pressure above the puck (boiler pressure + piston pressure) forcing more water into the puck thereby saturating it. Under certain conditions boiler pressure isn't enough to saturate the puck, so providing additional pressure from the piston will force more water in, this is when pulling the lever back up for a 'half Fellini' will contribute more water to the shot (but only to a point depending on whether or not the lever has already been pulled down enough to seal off the boiler).

One exercise you might try is placing a large bowl under the group without a portafilter and raise the lever to the top, releasing the pressurized water. Slowly pull the lever down until water stops spraying out. That will tell you at what point the piston has closed off water from the boiler and is no longer filling the space between the piston and the puck. I may be wrong, but I think raising the lever again at a point anywhere above this point will not add anymore water to the shot.

Another way to think about it is that with the lever up there is a constant supply of pressurized water (to a point, of course) at around .75 - 1.1 bar. The puck (and basket) provides resistance to the flow of water. This resistance is determined by many factors, the most significant being dose and grind, all other things being equal. More resistance (e.g., finer grind) decreases the flow rate of the water, increasing the amount of time it takes to saturate the puck. Increasing the water pressure with the piston will increase the flow rate of water, which help to saturate the puck more quickly. So let say you have a standardized procedure where you saturate for 10 seconds (pre-infusion). If the grind is on the fine side, it may not be enough time to fully saturate the puck. If you then pull your shot all the way through, closing off water before the puck becomes saturated, there will be less final volume in the cup. If you instead raise the lever back up before sealing off the boiler, you are essentially increasing the pre-infusion time, but not in reality adding anymore water because flow never fully ceased. So, to my way of thinking, doing a half 'Fellini' in this scenario mainly serves to ensure that the puck is fully saturated.
I hope I explained this well. I feel like I am talking in circles :-/
Jack
LMWDP #698

LObin

#13: Post by LObin »

jackdaddy wrote:Good point for me to try to elaborate on. Let's assume the puck has absorbed enough water to become saturated and maybe even some drips out. Let's also assume the lever is still in the fully raised position.
Oh. I see. We're talking about two different manipulations. I preinfuse for 5-10 seconds with the lever up (boiler pressure), lower the lever till the bottom of the basket is filled with coffee beads. Usually let a few drops fall in the cup before moving the lever back up to add more water to the cylinder. Only then do I do a full pull to complete the extraction.

I uploaded a video that I sent to a friend a few weeks ago. It's not a 40g yield (wasn't my intention) but demonstrates the technique I explained before and also the efficiency of a puck screen (mesh Aeropress filter cut to size).

Here: http://www.youtube.com/watch?v=KlhKnJV9z6w
LMWDP #592

jackdaddy

#14: Post by jackdaddy »

Yes. As I understand the various descriptions of 'Fellini' maneuvers, your method seems to be what I think of as a full. You are actually adding more volume to your shot. It's not unlike having a long pre-infusion, in which the pull doesn't begin until a drop or a few hit the cup before pulling the shot (what La Pavoni recommends, I think). The internet has so many descriptions of how to perform a Fellini move or what the purpose of one is, from puck saturation to gas removal. It is very interesting and I would love to hear more explanations from lever experts. I did my own version for about 2 years to maintain a consistent yield and to eliminate sponginess before experimentation lead me to longer pre-infusion times to achieve a similar but slightly better result. I find this to be especially effective with lighter roasts. I go with a very fine grind, 60 second pre-infusion and a 45 - 60 second pull, from between 7 and 9 bar. I get a consistent, nearly 1:2 yield ratio that does not seem to be over extracted, at least to me :-)
With darker roasts I go with a slightly coarser grind, a 30 second pre-infusion and a 30 - 45 second pull.
Jack
LMWDP #698

Rickpatbrown (original poster)

#15: Post by Rickpatbrown (original poster) »

LObin wrote:Oh. I see. We're talking about two different manipulations. I preinfuse for 5-10 seconds with the lever up (boiler pressure), lower the lever till the bottom of the basket is filled with coffee beads. Usually let a few drops fall in the cup before moving the lever back up to add more water to the cylinder. Only then do I do a full pull to complete the extraction.

I uploaded a video that I sent to a friend a few weeks ago. It's not a 40g yield (wasn't my intention) but demonstrates the technique I explained before and also the efficiency of a puck screen (mesh Aeropress filter cut to size).

Here: video
An interesting observation about the coffee drips as you raise the lever ... I dont notice any retraction or indication of water being pulled back from the puck.

Another observation on my own ... when I raise the lever for the first time after preheating, I get some water that comes out of the group (not the steamy shower that comes from the boiler at 4/5 high). Is this water coming from the piston sleeve? Maybe the Europiccola has some type of mechanism that allows for this.

Your shot looks good. I dont see any evidence of puck disruption.