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Crazy idea for a big Moka pot
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longwaytofall
Senior Member


Joined: 15 Jan 2013
Posts: 1
Location: SF Bay
Expertise: Just starting

Posted Tue Jan 15, 2013, 3:36pm
Subject: Crazy idea for a big Moka pot
 

Hi all,
This is my first post here. I am very thankful I found these forums, they have been a great resource for me!

So, I work at a machine shop, and decided I would like to build my own moka pot, but much larger. I would like to make about 160oz of coffee at a time.
My thought process on how to make the machine went sort of like this:
A moka pot is great, but in order to develop the pressure needed the water will be much hotter than 212f. This led me to look at ways to develop steam without heating the water as much, such as a second, separately heated chamber, or a small but very powerful electric heating element, or even design the bottom of the water chamber to trap an air pocket so a very thin layer of water is over the heated surface.
The problems with this, are that temperature and pressure can never really be controlled properly, and repeatable results would be hard.
This has led me to the idea of using compressed gas (co2) in order to provide exactly the amount of pressure I would like at the exact time I want it. A side benefit, the co2 dissolved in the water might help crema production.
One very nice feature is that I will install a valve at the top of the dispensing tube (which I would like to pour directly into an urn) that will allow me to control the flow rate completely independently of the pressure. I should be able to dial in the flow rate to the coarseness of the grounds, while keeping the pressure high to produce crema.

I will be building the unit to handle pressures well over 10bar, so I can get into espresso territory if I like.
Am I completely crazy here? Haha.
At this point (besides getting feedback on the idea as a whole) I need help designing the basket unit that will hold the grounds. Because the flow rate will be relatively slow and the amount of water passed over the grounds is a lot, shouldn't I make the basket long and narrow, rather than short and flat like espresso? I know that the shorter and flatter it is, the faster the extraction in espresso, and I am trying to slow it down as muchas possible.

Thanks for reading, and I look forward to your feedback!
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Owl
Senior Member


Joined: 30 May 2011
Posts: 37
Location: US

Posted Wed Jan 30, 2013, 10:15pm
Subject: Re: Crazy idea for a big Moka pot
 

That's very ambitious.

Why do you want to make so much coffee at one time using this method?
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jpender
Senior Member
jpender
Joined: 11 Jul 2011
Posts: 701
Location: California
Expertise: I like coffee

Grinder: OE LIDO
Vac Pot: S/S Moka Pot
Drip: Aeropress
Posted Thu Jan 31, 2013, 11:24am
Subject: Re: Crazy idea for a big Moka pot
 

Pressure to 10 bar with independent temperature, pressure and flow control -- that doesn't sound like a moka pot, it sounds like an espresso machine, albeit one that uses the stove as a heat source. I wouldn't call you crazy, exactly, just an enthusiast who doesn't mind trying to reinvent the wheel.

Full disclosure: I once attached a bicycle pump, air ballast, and valve to my stainless steel moka pot in an attempt to "pull a shot" at 9 bar.
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redkiosk
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redkiosk
Joined: 13 May 2012
Posts: 218
Location: Chicago Metro Area
Expertise: I love coffee

Espresso: Illy Francis-Francis X1
Grinder: Baratza Preciso w/ Esatto...
Vac Pot: Someday, very intriguing!
Drip: Trifecta MB, Kalita Wave...
Roaster: A sure path to divorce!
Posted Thu Jan 31, 2013, 2:21pm
Subject: Re: Crazy idea for a big Moka pot
 

Maybe you should put this project up on Kickstarter and see where it goes. You might be surprised. Take care!

Jim

 
The pathologically precise are annoying, but right!
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dyqik
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Joined: 7 Oct 2011
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Location: Cambridge, MA
Expertise: I love coffee

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Posted Thu Jan 31, 2013, 2:50pm
Subject: Re: Crazy idea for a big Moka pot
 

jpender Said:

Pressure to 10 bar with independent temperature, pressure and flow control -- that doesn't sound like a moka pot, it sounds like an espresso machine, albeit one that uses the stove as a heat source. I wouldn't call you crazy, exactly, just an enthusiast who doesn't mind trying to reinvent the wheel.

Full disclosure: I once attached a bicycle pump, air ballast, and valve to my stainless steel moka pot in an attempt to "pull a shot" at 9 bar.

Posted January 31, 2013 link

While we're on dirty hacks, my house mate hooked a bike pump and a pressure gauge up to his LP Europiccolo to get higher preinfusion pressure without overheating the boiler.
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germantownrob
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germantownrob
Joined: 2 Dec 2007
Posts: 2,152
Location: Philadelphia
Expertise: I love coffee

Espresso: Duetto 3, A Dead Oscar
Grinder: Vario-W, Preciso w/Esatto,...
Drip: Brazen
Roaster: Diedrich IR-1, HT B
Posted Fri Feb 1, 2013, 7:56am
Subject: Re: Crazy idea for a big Moka pot
 

I have used and loved moka pots for 25 years. Getting repeatable brews is about maintaining dose and grind and slight adjustments to maintain extraction. Not to stop you from experimenting but they do make moka pots large, http://www.bialettishop.com/MokaExpressMain.htm , 18-25 oz big enough?

I have never snaked a TC into the bottom of the reservoir but the temp that hits the grinds is not 212f, 205f is the highest I ever measured with a tight pack.
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jpender
Senior Member
jpender
Joined: 11 Jul 2011
Posts: 701
Location: California
Expertise: I like coffee

Grinder: OE LIDO
Vac Pot: S/S Moka Pot
Drip: Aeropress
Posted Fri Feb 1, 2013, 9:27am
Subject: Re: Crazy idea for a big Moka pot
 

germantownrob Said:

I have never snaked a TC into the bottom of the reservoir but the temp that hits the grinds is not 212f, 205f is the highest I ever measured with a tight pack.

Posted February 1, 2013 link

I have. Using a normal grind and heating rate I've measured both the reservoir water temperature and the grounds slurry temperature go over 100C near the end of a brew.

I'm curious, how did you measure the "temp that hits the grinds"? What kind of pot and how did you brew with it?
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germantownrob
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germantownrob
Joined: 2 Dec 2007
Posts: 2,152
Location: Philadelphia
Expertise: I love coffee

Espresso: Duetto 3, A Dead Oscar
Grinder: Vario-W, Preciso w/Esatto,...
Drip: Brazen
Roaster: Diedrich IR-1, HT B
Posted Fri Feb 1, 2013, 10:16am
Subject: Re: Crazy idea for a big Moka pot
 

jpender Said:

I have. Using a normal grind and heating rate I've measured both the reservoir water temperature and the grounds slurry temperature go over 100C near the end of a brew.

I'm curious, how did you measure the "temp that hits the grinds"? What kind of pot and how did you brew with it?

Posted February 1, 2013 link

All my pots are Bialetti's, I snake a TC down the neck to the grounds. The water in the base does not concern me with what temp it is at, I only care what the grind sees. I turn the gas burner off or move it to a cool electric burner the moment it starts to flow.

So I have heard many people say that a moka pot works in the 1 Bar area, not sure it is that high personally, but 15psi is just over 1 bar, water temp of water at 15psi is 257f, my espresso machines steam boiler when set to 262f is close to 1.5 bar. Water drawn from the boiler through a short amount of copper tubing comes out at 208f and can never be above 212f. So you could make a hole in the filter basket to measure the reservoir water while brewing but it has no bearing on what temp the grounds are seeing. Since the hottest the water could posiable be once there is no more pressure is 212f the grounds themselves will cool that down rapidly. The pot itself is cooling the water once it starts flowing up the funnel of the grounds basket, the entire top of the pot is well under 212f and has much more mass then the amount of water being heated, and this cooler temp is being transferred to the basket.

I will stick to my guns with 205f was the hottest a TC probe in the bottom third of the basket ever showed while brewing and that was a tight pack with very slow flow. 202f is more what I see with my normal pack.

I rarely use my moka pots anymore and when I do it is a Brikka I grab,  I find that widget lessens the variable of dose and pack.
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jpender
Senior Member
jpender
Joined: 11 Jul 2011
Posts: 701
Location: California
Expertise: I like coffee

Grinder: OE LIDO
Vac Pot: S/S Moka Pot
Drip: Aeropress
Posted Fri Feb 1, 2013, 11:54am
Subject: Re: Crazy idea for a big Moka pot
 

germantownrob Said:

So I have heard many people say that a moka pot works in the 1 Bar area, not sure it is that high personally, but 15psi is just over 1 bar, water temp of water at 15psi is 257f, my espresso machines steam boiler when set to 262f is close to 1.5 bar.

Posted February 1, 2013 link

Unlike the boiler in your espresso machine, a moka pot reservoir contains air that contributes to the total pressure. So 15 psig does not imply 250F in this case; it will be lower. As the moka pot brews the head space volume increases which means the water temperature has to go up to compensate. This is the primary reason (although not the only one) for why the water and grounds temperatures both rise throughout a moka pot brew cycle.

germantownrob Said:

Water drawn from the boiler through a short amount of copper tubing comes out at 208f and can never be above 212f. So you could make a hole in the filter basket to measure the reservoir water while brewing but it has no bearing on what temp the grounds are seeing. Since the hottest the water could posiable be once there is no more pressure is 212f the grounds themselves will cool that down rapidly. The pot itself is cooling the water once it starts flowing up the funnel of the grounds basket, the entire top of the pot is well under 212f and has much more mass then the amount of water being heated, and this cooler temp is being transferred to the basket.

Posted February 1, 2013 link

Nonetheless, when I measured the temperature in the water and the grounds I found that both exceeded 100C near the end of the brew.

germantownrob Said:

I will stick to my guns with 205f was the hottest a TC probe in the bottom third of the basket ever showed while brewing and that was a tight pack with very slow flow. 202f is more what I see with my normal pack.

Posted February 1, 2013 link

I don't doubt that you measured what you measured. I'm just curious about why what you observed is different from what I did.

You ran a probe down from the top, through the upper screen, and into the bottom 1/3 of the grounds -- is that right?
What type of probe did you use? Do you know what its response time is?
What model and size Bialetti?

germantownrob Said:

I rarely use my moka pots anymore and when I do it is a Brikka I grab,  I find that widget lessens the variable of dose and pack.

Posted February 1, 2013 link

I'm looking forward to brewing with a Brikka. It's on my list.
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germantownrob
Senior Member
germantownrob
Joined: 2 Dec 2007
Posts: 2,152
Location: Philadelphia
Expertise: I love coffee

Espresso: Duetto 3, A Dead Oscar
Grinder: Vario-W, Preciso w/Esatto,...
Drip: Brazen
Roaster: Diedrich IR-1, HT B
Posted Fri Feb 1, 2013, 12:35pm
Subject: Re: Crazy idea for a big Moka pot
 

My espresso machine boilers most certainly do have air in them.

Probe I would have used then Click Here (www.sweetmarias.com) not the fastest but fast enough.
I used a Musa 6cup and a Moka Express 6cup, I was trying to see noticeable difference from SS and Aluminum. I also have the 10 cup SS and 1,3, and 6 in aluminum. The 3 cup is my favorite.

Not sure where you measured temps but you mention at the end of the brew, I am long off the heat before that, the aluminum pot response is the quickest when removed from the heat.

My last espresso machine I created a leak when I completely filled it with water for a descale. Where it went horrible wrong was when I heated a vessel that had no room for its contents to expand, my intention was not to heat to full temp 255f temp but heat the solution to 200f, I walked away and got distracted. 35 min later the tell tell his was coming from my machine and it wasn't the obviously not working safety pressure valve. All boilers have this safety valve, if they didn't it is a bomb, I am just lucky water found an escape in my case.
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