Hey guys,

I'm struggling with the shots from my La Pavoni Pro Millenium lately.
At the end of each shot i get big bubbles on the downside of my basket.
It feels like I can't push all the water through the puck, but the lever is in the lowest position when the bubble develops.
I also checked the adjustment of the piston.

I'm using a Kinu M47, the IMS Precision Shower and Basket. I do WDT and RDT plus i use a leveler/distributor.
Most of the time i drink bright/medium roasts.

What do you think could solve this problem?




Is it channeling?
Maybe my beans are too fresh and they cause the bubbles?
Do I need to adjust the piston in a different way?

Hoping to find some answers.

Thank you,
Sebastian

So you can change your technique to reduce air or add this new device

https://coffee-sensor.com/product/airbu ... oup-heads/

Doesn't sound like a likely possibility and the other answers seem more on target but if you ever removed the lever from the group it can be put on upside-down which changes the travel of the cylinder. The holes on the lever forks should be close to the bottom, not the top.

A few problems with my old La Pavoni Europiccola

I agree it might be the air in the cylinder, but I wonder if it's also partly because you're pulling it too hot? Are you measuring the grouphead temperature? Your coffee does look foamy even in the cup. This is just because I remember such discussions from elsewhere, and I never had this issue. I always measured the temperature.

The lever is mounted correctly.

I always flush the machine when it's at 1.0 bar with the portafilter locked. Then I open the steamvalve for letting the pressure a bit off.

Then I usually pull a shot with my wife's decaf beans and then I pull my shot. So normally the temperature shouldn't be too high, right?

The coffee sensor air valve looks interesting, maybe worth a try. But they write u need their piston. So it might get expensive.

What I'm going to try next is to reduce the amount of coffee. Most of the times I use about 17g in the double basket and I end up with 30-35g of liquid.

Actually flushing might heat up the group too much. Usually what is nowadays done with the millennium groupheads at least is something called "dry pumping". That is pump only so that no water comes out. This circulates the water between the grouphead and the boiler. I do recommend measuring the temperature though so you don't have to guess so much.

17 grams sounds quite a high dose, especially if the beans are in the medium to dark range of roast or otherwise not dense. I've been able to dose 18 grams with a very dense light roast once but I usually standardise to 15 to 16 grams. With some very dark roasts I've had to go 13 grams in the double basket.

Edit to add that above advice is on point for temp surfing and also dosing. Could be taking the grind finer might help too. LP likes fine grind overall for traditional pulls.

This is probably a three subtle tweaks kind of problem. A little bubbling at the very tail end of the pull is normal, I only worry about it if I didn't pull my cup or if it starts before the lever is fully down. If it did start before full down I usually find its a combo of being over temp and I messed up my initial lift technique. Though sometimes it happens with a coarser grind with turbo shots no matter what I do.

The new coffee sensor gear is supposed to fix the air bubble issue but I have not purchased it to try it. Hoping others who have will chime in on it's use.

However there are ways to minimize the bubbles and also get higher end volume too. First off buy some cheap temp strips for your group head. They aren't perfect but they can easily tell you when you are over temp and need to cool the group. I find the tap water cooled portafilter and a short wait is all it usually needs.

The lever technique I use is a slow lift to the point that the water inlet is just barely open and let the group fill until the lever wants to lift up to the top. Let it up with light guidance at that point because it has now driven most of the air out of the chamber and water is pushing the piston up. Once it's topped out pull it however you had planned to complete but try to decline pressure near the end.

Mostly it's a sound and feel thing. If the water goes whoosh and you feel a thump on the lever you opened the inlet too much and probably won't clear all air that pull or feel the lever want to rise. The sound you want is similar to a low hiss with a low thrum from the water in the handle. If you nail it you will feel the lever want to rise. At that point pull as you prefer and enjoy a much earlier start to lever resistance.

Thanks for your replies so far.

I'll try some of your hints for my lever technique.

When I don't flush the pavoni before my first shot, the coffee tastes way too acidic and underextracted. It's definitely too cold.
This morning I did'nt flush the machine and pulled the Colombian decaf for my wife's cappu. Again a big bubble.

The taste of my shots are very good, the only thing that disturbs me are these bubbles, because they destroy the "beauty part" of the cup.

I just watched the video about the Airbuster from coffeesensor on YouTube.
Can you tell me why there is so much water left on the puck after the shot?
That seems very strange to me.
I want a dry puck and not a muddy one..

I can exclude the freshness of the beans. 2month old beans from Ethiopia also have the bubbles.

When I started making coffee with my pavoni 5 years ago, I never had this problem with dark roasts.
So maybe it has something to do with the finer grind and the air inside the system.

What you could try before spending on air buster or so is as follows:

- Pump the lever when the machine is cold. Do this until you get a good amount of water out
- Warm the machine up
- When you do the "false pressure" purge also do some dry pumps (only pump the lever up to the level that the water does not come out)
- Close the steam and keep on doing dry pumps until the grouphead is very hot to touch
- When pulling a shot first let some water on top of the puck. I do this so that I can see a certain amount of water on the puck, not too much that it would spill out when locking in
- Hold the lever just below the water exit point and lock the portafilter in
- Now take the lever up.
- Do some small pumps at the top, basically using the "empty" area of the pull. Just up and down, even quickly. A few is enough
- Now do your regular pull

The "late lock-in" described above should be fairly easy holding the PF on your left hand and using the lever with the right.

Anyway, just a couple of ideas to try before getting extra bits and pieces.