Vacuum Pot Technique

[Bertilak]

• First, I let the water simmer a bit (60 secs) after all the water went "north" and before adding the coffee. My theory is that the gas inside the pot needs to be water vapor, not plain old hot-air. Otherwise, what's to condense after the pot is off the heat? Give the simmering an extra 60 secs to blow out all the air.

I think part of my problem (maybe even most of it) might be related to this. I always make a partial pot. This means the pot starts with extra air. Could be that there is a tendency to not have enough water vapor in the pot to complete the draw-down.

 

[Jasonian]

Just give it more time. It isn't just water, it's also air. A vacuum is a vacuum is a vacuum. Water is more quickly displaced than the air, however, and it just may take more time to clear the lower chamber sufficiently to get an adequate draw-down.

 

[jwhite]

UPDATE:

I am having better results now!

• First, I let the water simmer a bit (60 secs) after all the water went "north" and before adding the coffee. My theory is that the gas inside the pot needs to be water vapor, not plain old hot-air. Otherwise, what's to condense after the pot is off the heat? Give the simmering an extra 60 secs to blow out all the air.
• Next, Using a coarser grind has helped. I also didn't knock the last bit of grounds out of the holder. Just used what dumped out w/o any extra encouragement. I think this might have held back some fines due to static.
• Finally, I took jwhite's suggestion and got a sample grind at the store. Used for my two most recent pots. This worked well. Since my sample is now used up I will see if I continue to get good results, or if things regress. (Took me a while to get to this since my car was in the shop for 5 days.)

Glad to hear you're having greater success, I'm sure you'll nail it down soon.

As far as partial pots go have you ever considered brewing a full pot and putting the remainder in a glass pitcher in the fridge (no ice). I just make a full portion of whatever brew method I'm using and put up the rest, and while I do prefer it immediately after brewing it's really pretty good and nice to have iced on these hot days.

 

[Bertilak]

FINAL(?) REPORT:

Making a full pot works better than making a partial pot.

When making the full pot I went to a less-coarse grind, although a bit coarser than in the past.

I put the grounds into the top part before inserting that into the base. I did this because I anticipated the water bubbling up to the very top, making it hard to put the grounds in after the fact. I let the water simmer for a minute in the base at a lower heat before inserting the top part.

Draw down started at about 15 seconds after taking it off the heat. Draw down of the full 8 cups took the same or less time than it did for a 6 cup load.

Ended up with a nice pot. Very clean and clear coffee.

I think the Yama-8 is designed for making a full pot. Partial pots are possible but tricky.

Oh yes, the Cory rod is better than the spring-loaded cloth filter. Doesn't get stained or collect old oils. Easier to clean (just rinse it off).

 

[jwhite]

Congratulations!

 

[JPDyson]

Bob, vacuum pots do tend to work best w/full pots in general. I think this is because a certain amount of water will necessarily stay down in the bottom pot, meaning you're actually brewing slightly concentrated coffee in the top pot and diluting it back down with the water that's left in the bottom. If you reduce the total amount of water, the water that stays down does NOT reduce, so you're brewing with (proportionally) far less water up top. I hope I explained that well...

Edit: It occurs to me, in explaining that, there's advantage to the rounded bottom counter-top designs, in that they should hold less water down than flat-bottom models would. Once the water is low enough for vapor to escape from the bottom vessel, no more water will travel upward. If you look at the round bowl design, it's easy to see that leaves less water down. Again, hope that makes sense.

 

[ravkesef]

I agree with those who say that your grind may have been too fine--especially if your Cory filter is letting excessive grounds into the coffee. Here's a trick learned from the Blue Bottle in SF: When you take it off the heat source, put it on a trivet or a cork, and then wrap a cool, damp towel around the carafe. This will start the draw down and speed it up, so that in a matter of seconds, you will have a full carafe, or clear, clean, rich coffee.

 

[Jasonian]

I agree with those who say that your grind may have been too fine--especially if your Cory filter is letting excessive grounds into the coffee. Here's a trick learned from the Blue Bottle in SF: When you take it off the heat source, put it on a trivet or a cork, and then wrap a cool, damp towel around the carafe. This will start the draw down and speed it up, so that in a matter of seconds, you will have a full carafe, or clear, clean, rich coffee.

That can be risky if you don't know what you're doing.

Touch ONLY the parts where there is no liquid touching. Hario glass is typically the best one for this technique with their "no breaking allowed" policy.

I wouldn't try it with my Bodum, but I do it as a part of regular procedure with my Hario TCA-2. I'm not saying not to try it.. I'm saying beware if you do.

 

[JPDyson]

This is designed to decrease the temperature more rapidly, which more strengthens the vacuum in the lower chamber. If it doesn't equalize quickly enough (for example, filter clog) you run the risk of implosion.

 

[Bertilak]

Bob, vacuum pots do tend to work best w/full pots in general. I think this is because ...

My theory is as follows.

When steam (water vapor) cools to below 100C it goes through a phase change from gas to liquid. As a gas, steam creates great pressure in a constrained volume. It expands to fill that volume, in our case this being the volume of the pot. As it cools and goes through its phase change it reverts to a few small drops of water that take up a trivial volume, leaving behind a vacuum. Also, the steam exerts a great deal of pressure and the liquid water exerts no pressure.

When the gasses in air cool from above water's boiling point to below they do not go through a phase change so their contribution to a pressure difference is trivial compared to that of the condensation of steam.

If you start with a full pot of water there is very little air in the pot so during the draw down stage it is mostly steam in the lower chamber. It condenses (the all-important phase change), causing the vacuum. If you start with less than a full pot of water, there is more air in the mix and therefore less steam. Since it is the condensation of steam that drives the process a partial pot doesn't have as strong a vacuum.


EDIT: Since I haven't quantified any of the above, it is hard to say exactly how important things are. For example, if starting with a partial pot (and therefore "lots" of air), how much of that air is driven out by the initial boiling process? I know it isn't ALL the air since the pot is open and the gasses will do some sort of vapor pressure equalizing. But, I think the tendency I describe above is there, it is just the extent I can't be sure of. Another complication: air itself has differing amounts of water vapor (humidity) and I don't know if that has a non-trivial effect.

 

[JPDyson]

My theory is as follows...

So, if this is correct, a lacking vacuum in the bottom pot would result in slower draw-down. However, if enough positive pressure is generated to expel the water from the lower chamber by simply heating the water until it boils (and before somebody gets all huffy because I said "boil" you'd better look up the definition) then one would suspect that enough negative pressure would exist when it is cooled for draw-down to occur. Add the fact that gravity impedes the initial reaction and assist the latter, I suspect initial water volume not to be the primary contributing factor.

To put it more succinctly, brewing 3 cups in my 5 cup, I still get a good draw-down, so I'm not inclined to believe that's the problem. I think solubility is to blame; too much water stays down when you do a small pot, so it can't effectively wash out your soluble solids.

 

[yakster]

I regularly make 5 cup pots in the 8 cup Yama with a lock-in glass filter rod so that the Wife and I can enjoy a nice cup on the weekend. I'll only make 8 cups if we're having company.

My method is to use a fairly fine grind, slightly finer then pour-over. This seems contrary at first, but many grinders will churn out more fines at the coarser setting and the grinds consistency is better at a finer setting. I heat the water from cold in the bottom part of the pot and when the water is approaching the correct temperature, I'll mount the funnel on top and let the water rise completely and come up to temp before adding the grinds.

For the five cup, I let the coffee steep (pushing the grounds down with the Yama spoon or a wooden spatula) for two minutes before pulling the pot from the heat to start the draw down. I fear that too short a steep can lead to inadequate vacuum to pull the coffee down through the grounds, this may be something to look at. A friend on another forum suggests that you increase the heat for the last ten seconds to blast any fines up away from the glass rod before you start the draw-down, I sometimes do this, especially with a darker roast which can be trickier, but I seldom find this necessary. He claims that this ended his battle with stuck pots.

What ended my battle with stuck pots and got me making siphons just about every weekend was a grinder upgrade. I was using the Cuisinart "false-burr" grinder so common and the fines it was churning out were causing no end of trouble. I don't know how it would work with a cloth filter as I've never used one, but once I got my Vario and took up the siphon again, I've had no problems.

One trick I use to keep the coffee warmer in the pot is to invert an espresso demitasse over the opening of the pot to trap in the heat so I can enjoy my first cup before coming back for a refill.

 

[Bertilak]

I regularly make 5 cup pots in the 8 cup Yama with a lock-in glass filter rod ...

Thanks. I think there is merit to your technique -- especially cranking up the heat to blow away any fines.

 

[yakster]

I've heard that technique called the "rumble in the funnel" but I like to think of it as the Hoople thurst.

 

[global_dev]

i pretty much only do a 4 cup level in my 8 cup yama since it's only me. my drawn do is quick enough, i am using the cloth filter. I let the water boil in teh carafe alone, the coffee is ground and put in the top, which sits in the black plastic top/holder, then I add the top and continue on... i am using fine grind (low bias) on a Capresso Infinity

 

[Bertilak]

Sorry to bump this thread up without adding any real technical content, but I just want to say thanks to all who contributed ideas. Things are working much better for me now. It's hard to put my finger on what made the biggest difference since in the long run I am not doing things very much differently than I have in the past, but I think the following are the keys:

• Minimizing fines, or their effect. This includes using a slightly coarser grind, not "tapping" the very last bit of grinds into the mix. "Blowing" them out with a bit of extra heat just before removing the heat completely.
  
  
• When making less than a full pot, being sure there has been enough simmer time to replace as much ambient air from the lower chamber as possible.

So again, thanks for all the advice. It did help!