Curious if anyone else encountered this:

https://youtu.be/X_NGmMkg43Q

at around 10-15s into the extraction an air bubble appears and stays there for the duration, sometimes it pops (or I pop it by blowing on it) and another one forms. This happens on pretty much every extraction, on super fresh and rested coffee, normal and decaf.

Any ideas would be appreciated as I'm at a loss as to why this happens.

Regards,
T.

Maybe the problem is with the grinder?


Just kidding. Seems normal as there's definitely some air in the system as to how Cremina works. As you displace the water, the air sometimes will get pushed out together. It probably depends on how much air is gotten rid from the system before (try purging some water through see if it reduces).


Some videos that showed bubbling to a certain extent:

time - 0:44 time - 0:29 time - 2:12

Nothing wrong with your Cremina, that is pretty much normal.

Agreed with the answers so far, chances are your Cremina is fine, enjoy it.

Plus, I have tasted some of those air bubbles, and they taste great!!

There is surely some air/gasses trapped inside the coffeecake which can't escape upwards during the shot. May be a longer preinfusion could help. Interestingly I have this phenomenon more with my Olympia Club (could be accindental though).

Yes, I typically only get the air bubble when I either do not pre-infuse (using "Fellini" and / or raising the lever and pausing for 5-10 seconds), or when I pull too rapidly on the downward stroke, Both force the water too quickly through the coffee resulting in a potential air pocket, where part of the coffee is not wet or as wet as other parts. Eventually the drier part will get wet, and that air pushed through, and when you see the bubble form. In summary, you could be getting uneven wetting of the puck. Or, it is possible your grind / dose / distribute / tamp routine is leaving air pockets in your puck.

Do you employ the "Fellini" method? When you raise the lever, how long do you wait before starting your downward stroke? To me it appears you are pulling before there is any pre-infusion... your method still works fine, but may be the root cause of your bubble. It also appears you are pulling fast as the "cone" is rather large before the air bubble appears... but I cannot be sure of this because I cannot see your lever / pull stroke. It also could be pressure related....

It is also possible your grind / tamp routine is leaving air pockets in the puck. Did you try WDT, or change your distribution / tamp methods slightly to see if the air bubble still exists?

In other words, try a few different things and see what changes - things like a single or double Fellini, longer wait when you raise the lever, or a slower downward pull and see if that helps. Then if nothing changes, tinker with your grind / tamp routine.

When I assure a nice even pre-infusion, I probably only witness an air bubble once every 25 -50 shots (I don't count but it is infrequent). And then it is probably more to a poor distribution / tamp than anything where I left some air in my puck.

Thanks for all the replies.

Ah yes, the grinder issue

I'm grinding straight into the basket and the way the grinder kicks out the grinds allows me to fill it evenly with pretty good 'directional' grinding as well (ie. I decide where the grinds go). I tamp very lighly, almost only to flatten the top and get an even surface, so that might as well be an issue. The lift of the lever is slow and I do hold it on the top for around 6-8sec, so there's plenty of time for preinfusion. I often leave it up till I see beads of coffee on the basket surface and then press down. I might play around with how heave the push down is.

Regards,
T.

You using the prototype for this one?

As to the bubble, I don't have a Cremina but the pull looks similar to when I don't bleed my pack I completely but leave a bit of air so I second the notion of improving bleeding. Hehe guess it doent help much to agree that the air is making the air though:) but the notion of tamp causing it seems a bit farfetched to me, or even that the wetting of the grinds does. However a longer preinfusion might allow more time for air to spelt evacuate but the real issue would probably be temp consistency if air is staying in for some reason...

Lately I have been doing things to prevent air being pulled through the puck in either direction, especially up! I also have begun to do a "double tamp" For the first one I use a convex tamper, and press it down quite hard, about the downward force of the mass of 15 kg on Earth! Then I switch to a flat one and press it down the same way. This seems to reduce the tendency of the espresso to emerge too much from the edges of the filter basket because it results in the edges being eventually pressed a bit harder than the centre. (With La Pavoni second generation groups I make very sure that there is no air left in the group before giving any thought to pulling the first shot.)

I always have a cup and the portafilter ready for use. Although I have three very different types of groups on my lever machines, a first generation La Pavoni, two second generation ones, and a Micro Casa a Leva I always initiate things the same way. I push or pull the lever until it releases JUST A BIT of water. I move it just enough to stop the flow, and as fast as possible attach and lock on the portafilter. As soon as possible after that I move the lever to the position to flood the chamber below the piston with water. I push the handle enough so just a bit of espresso emerges, or with the MCAL I slowly release the handle until a bit of espresso emerges, and then I move the lever back to the position to top off the water in the piston chamber. I then apply the pressure (or with the MCAL let the machine apply the pressure) and make the shot. This always gives the same volume of espresso with a given machine. With the 1st and 2nd generation La Pavonis it is a good thing to use an MCAL basket so the large volume does not result in too dilute espresso that has had bitter tasting things eluted into it toward the end. To me spongy shots are very bad because their volume is erratic.

rpavlis wrote:
I always push or pull the lever until it releases JUST A BIT of water. I move it just enough to stop the flow, and as fast as possible attach and lock on the portafilter. As soon as possible after that I move the lever to the position to flood the chamber below the piston with water. I push the handle enough so just a bit of espresso emerges, or with the MCAL I slowly release the handle until a bit of espresso emerges, and then I move the lever back to the position to top off the water in the piston chamber. I then apply the pressure (or with the MCAL let the machine apply the pressure) and make the shot.

This is may be the most useful hint avoiding airbubbles during your pull.