Posted Tue Jun 12, 2012, 5:28am Subject: Re: Moka pot pressure
jpender Said:
Gregg, in the Illy video could you tell if the 1.1 bar represented a typical peak value or an upper limit?
Of course it depends on grind/tamping. I've brewed with an espresso grind and the safety release popped every time. But such a fine grind is on the fringe of what most people normally use. Illy actually sells cans with a moka grind, something between espresso and drip.
I did an experiment:
I took off the safety valve and attached a hose through which I could direct pressurized air. Then I filled the water chamber with near-boiling water, assembled the pot (with coffee loaded) and applied pressure sufficient to achieve what I judged (by eye) to be a "normal" flow. That is, one that was continuous yet slow, so it would take about a minute to push out about 150 ml of water.
I tried this with 6 different grinds. Five were from my Kyocera grinder (adjacent steps that I've labeled #0 through #4) and one was pre-ground Peet's from the supermarket (labled "PG"). The #0 was very fine, the #2 was in range for what I use as a moka grind, and the #4 was on par with the Peet's. No tamping.
In order to maintain the same flow rate I had to steadily increase the pressure over the minute or two it took to push out the water. This is why there is a range of values for each grind.
Just thinking, couldn't you just plumb in a T-connection in the safety valve port with the safety valve on one leg and a pressure transducer (or even a schraeder valve which you could attach a standard pressure gage) on the other?
Then, just make some moka pot coffee and measure the pressure directly? I'm just scanning the thread, so I'm prolly missing something.
More importantly, how did the results taste? LOL
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
jpender Senior Member Joined: 11 Jul 2011 Posts: 401 Location: California Expertise: I like coffee
Grinder: Kyocera CM-50 Vac Pot: S/S Moka Pot Drip: Aeropress
Posted Tue Jun 12, 2012, 9:03am Subject: Re: Moka pot pressure
Netphilosopher Said:
Just thinking, couldn't you just plumb in a T-connection in the safety valve port with the safety valve on one leg and a pressure transducer (or even a schraeder valve which you could attach a standard pressure gage) on the other?
Then, just make some moka pot coffee and measure the pressure directly? I'm just scanning the thread, so I'm prolly missing something.
There are two things that need to be considered. One is minimizing added headspace volume and the other is protecting the sensor from the heat source and the hot vapor. It's something I plan to do eventually but at the time it was a lot easier to just plug in a pump.
I didn't record any tasting notes but as I recall they were a little weird.
After I finished but before tearing everything apart I tried to pump the system up to 8 bar to "pull a shot" through my trusty 25 year old moka pot, just for fun. I loaded and tamped finely ground coffee, added near boiling water, and started raising the pressure. But the plastic tubing and epoxied connection to the air ballast (a 2 liter coke bottle) just weren't up to the task and air began leaking at 6 bar. I opened the valve anyways and the connection to the moka pot itself promptly failed. This is probably something I should have filed under your silly coffee tricks thread.
jpender Senior Member Joined: 11 Jul 2011 Posts: 401 Location: California Expertise: I like coffee
Grinder: Kyocera CM-50 Vac Pot: S/S Moka Pot Drip: Aeropress
Posted Tue Jun 12, 2012, 9:14am Subject: Re: Moka pot pressure
blekk Said:
Hi jpender thanks for the reply. I have a Brikka and it has the 15mm safety valve for which I assume has a higher rating due to the design of the Brikka but I would think it would only be about 0.5 bar more then the standard Moka pot.
That's a great idea setting up a test bench btw, Im not sure why I didn't think of it (Mech Engineering student)..... I might give it a try once I finish my exams this week.
I don't have any idea what the differences are between the two sized Bialetti valves. Maybe they're just different sizes for different pots but the same rating?
If you do the test post up your results. I'd try it but my pot is not a Bialetti and it's safety valve is old and seems to release a little too easily.
edit: I emailed Bialetti and asked about the pressure threshold but the person who responded said he didn't know, just said to keep the screen clean.
Posted Tue Jun 12, 2012, 1:17pm Subject: Re: Moka pot pressure
jpender Said:
... After I finished but before tearing everything apart I tried to pump the system up to 8 bar to "pull a shot" through my trusty 25 year old moka pot, just for fun. I loaded and tamped finely ground coffee, added near boiling water, and started raising the pressure. But the plastic tubing and epoxied connection to the air ballast (a 2 liter coke bottle) just weren't up to the task and air began leaking at 6 bar. I opened the valve anyways and the connection to the moka pot itself promptly failed. This is probably something I should have filed under your silly coffee tricks thread.
ROFLOL! I love it - a moka-spresso. That's friggin' hilarious and brilliant at the same time!
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
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