I was having the same problem as Gardoni with my Europiccola and the same batch of black cat, so we made a video with my gear as well. Except it turned out to be one of the better shots I've ever pulled on my machine! drat! just when I needed everything to suck so we could diagnose the problem, things go and get all "better"...

Anyway, while the extraction itself was pretty good, and the coffee tasted wonderful, there were still some small bubbles in the shot. They can't be seen in the video -again because of low compression quality. This was done from a cold machine doing a fellini single pull ( in other words about 1.25 pulls):

[youtube]http://youtube.com/watch?v=kD_a9ROqrms[/youtube]

But here's a screenshot from the same video that shows the small bubbles we're talking about.



Obviously not as bad as the shot on the silvia, but still there's bubbles. Can it be temperature related? maybe we should calculate our temerature surfing for water boiling at around 198° as it leaves the group?

At an altitude of 2240m (7700ft), it is not only the boiling point of water that is affected. The partial pressure of CO2 in the atmosphere is likewise reduced.

Perhaps some of what you are seeing with the "Bubbling Black Cat" is outgassing of excess CO2. In the past you may have used less fresh beans (that have already completely outgassed), or beans that were roasted locally at altitude. These wouldn't have as much tendency to release CO2.

I didn't really like chemistry all that much, and was not a very good chemistry student, so feel free to completely disregard ;-}

Jim

Keep in mind that a bottomless portafilter tends to produce a larger bubble texture in the crema. It is the nature of the portafilter. I actually prefer a spouted portafilter and only use my bottomless when diagnosing a problem. I prefer the finer textured crema of the spouted portafilter over the more arid crema of the bottomless extractions.

Based on the video and photo, I would say that is what is causing those medium sized bubbles. Try it with your spouted portafilter, I bet those medium sized bubbles go away with little to no loss in crema volume. Or try holding the cup closer to the portafilter so the crema does not drop as far. My bottomless shots look almost exactly like that.

You could also place the cup further to the side so the stream runs down the wall of the cup, or angle the cup so the crema lands on the upper portion of the wall and flows down gently to the cup base, but that is hard to do with a lever machine.

gardoni wrote:The purpose of this video was to be able to portray a pour in real time so as to better diagnose the causes of the bubbly shots and their dissipating crema.

I really appreciate the production values of your video. Love the music, intro, credits... so much so that I forwarded it onto Matt Riddle of Intelligentsia, current USBC champ and shot pulling robot.

Me: This is weirdly compelling. I've never seen a BC pour like that... bleech.
Matt: I have no idea..... that looks terrible. I've never seen shots pull like that.

Swell.

As Dave noted, this could be the same "bubbly" problem reported earlier. I'm still putting my money on runaway temperatures due to the heating element kicking on and the difference in boiling point. The only shots I've seen that extracted like that were from HXs that were not flushed. The steam makes an EXPLOSION of burgeoning cone crema. Bitter, foamy, bleech.

If you are temperature surfing, I would back off the pause so you'll get more extraction time before the heating element kicks in. Or it may be that the stock thermostat setting is just too hot for your region...

chino wrote:Anyway, while the extraction itself was pretty good, and the coffee tasted wonderful, there were still some small bubbles in the shot.

If the above assumption about Silvia is correct, your La Pavoni is pulling better shots because it's brew temperature is lower. The small bubbles you saw are typical of bottomless extractions. A quick swirl or thunk / swirl will eliminate them.

cannonfodder wrote:Based on the video and photo, I would say that is what is causing those medium sized bubbles. Try it with your spouted portafilter, I bet those medium sized bubbles go away with little to no loss in crema volume. Or try holding the cup closer to the portafilter so the crema does not drop as far. My bottomless shots look almost exactly like that.

I knew I should've bought an extra portafilter before slicing this one up! no turning back now...

But Gardoni and me also seem to have a problem with the persistence of the crema. I find myself rushing through the milk frothing process just to make it in time to see the crema die out... There's never enough for me to do a proper latte art type pour! We showed this in the silvia video, using the spoon. That was just about a minute after switching off the pump. The duration is about the same with shots from my europiccola. Any suggestions?

Dan,

Thank you!

I am glad you like the videos. Chino really knows his stuff in the editing room. I have a question though.

when you say:

If you are temperature surfing, I would back off the pause so you'll get more extraction time before the heating element kicks in

What exactly do you mean? I use the reverse temperature surfing technique that you once described in another post. I activate the pump until the light comes on. I then wait until the light goes off and count 2 minutes, then pull the shot.

What do you think?

Sincerely,
Gardoni

gardoni wrote:What do you think?

My assumption is the stock thermostat temperature is too high for your locale. So taking advantage of Silvia's HUGE deadband, we try to catch the widest swath of the lowest part of the cycle before the heating element kicks in. So for example, if the heating element takes 5-10 seconds to significantly affect the brew temperature, reverse surf until the resulting brew time is at least 15-20 seconds of the pour before the heating element kicks in.

I'm doing all this from long-dormant Silvia memory, so apologies for my vagueness. This sort of slow-motion temperature machinations must be really tiresome...

Thanks for the advice Dan,

So I tried to broaden my surfing time this morning. I took into consideration your reply and instead of waiting 2 minutes I waited for 2 minutes 30 seconds. The results were surprising, my cone was much thinner and it seemed as if the boiling temperature problems seen in the video were not there anymore. What do you think? Does 2 minutes 30 seconds seem like too long to you?

Sincerely,
Gardoni

Hello all,

I wasn't sure whether to start a new thread with this or not but I've also been seeing curious extractions with my Silvia. It's new, and I've got it pretty much dialed-in, but during extractions I often get an air bubble in the center of the extraction which forms underneath the main cone, and eventually causes the cone to twist off to one side. I can't correlate the appearance of this bubble with changes in my technique. Any ideas what might be causing this?

It's not the same as the drastic effect Gardoni is seeing: aside from this bubble, the pour looks fairly normal and the shots taste good so this is just a curiosity really.

I'm only about 300ft above sea level and I do make sure the tank and boiler are full before pulling a shot.

Cheers,

Dave

Edit - here's a video of an example of this effect (:oops:). The shot suffers a bit of crema-collapse and also for some reason when I stop the shot the pf handle is getting 'sucked-up,' which doesn't happen with my spouted pf

But how does the shot taste?