elaineculver Senior Member Joined: 11 Oct 2006 Posts: 3 Location: Victoria BC Expertise: I love coffee
Posted Sat Oct 22, 2011, 7:10am Subject: Pyrex Silex Glass Vacuum coffee pots
Can someone tell me if the top glass vessel with the siphon should have a full inch of clearance in the bottom pot when it is securely sitting on top? I was given this pot and with a full inch of water never siphoning up to the top vessel I'm thinking somethings not right. Thanks for any advice.
There should be (from memory, estimating) a good 3/4" gap between the glass syphon tube and the bottom of the lower vessel when the pot is fully assembled. There will also be about 3/4" of water left behind, which is not a coincidence. Once the water level is low enough that it's near the bottom of the tube, the pressure can equalize without forcing water upward.
As to WHY it's designed this way, well I have to assume it's along the same reason that you don't want to heat an empty pot on the stove (not to rule out other reasons, but that one occurs to me immediately). Maybe this gap also determines how much pressure is ultimately generated in the lower vessel, and is thusly engineered.
dtlord Senior Member Joined: 13 Mar 2009 Posts: 99 Location: Wisconsin Expertise: I live coffee
Espresso: Bezzera BZ07sde Grinder: Super Jolly, Virtuoso Vac Pot: Silex Victory, Cory, Sunbeam... Drip: pour over w/ mesh or paper Roaster: A nice guy named Roy
As to WHY it's designed this way, well I have to assume it's along the same reason that you don't want to heat an empty pot on the stove (not to rule out other reasons, but that one occurs to me immediately).
I have a vintage Vac pot and yes, there is a gap and yes, the reason is to not "boil" the bottom pot dry. If you don't have a constant pressure from the bottom pot, you can't hold the coffee in the top pot. No water heating in the bottom means there is no pressure to hold the coffee "up".
In real life, my name is Wayne P.
Feed the newbs, starve the trolls and above all enjoy what you drink!
I have a vintage Vac pot and yes, there is a gap and yes, the reason is to not "boil" the bottom pot dry. If you don't have a constant pressure from the bottom pot, you can't hold the coffee in the top pot. No water heating in the bottom means there is no pressure to hold the coffee "up".
I suppose the presence of water is beneficial, as water vapor expands with greater force than does air, but strictly speaking, it is not a requirement. That is to say, air alone will expand with heat (go fill a balloon and microwave it for proof). However, it occurs to me that you couldn't totally eliminate water anyway. There would need to be a gap for the purpose of transfer, which means there will necessarily be an amount of water remaining. I guess the important question is "why so much"? Why not an 1/8th inch gap - surely vapor could pass if the gap were that small. Would that have a detrimental impact on the amount of pressure in the system?
I suppose the presence of water is beneficial, as water vapor expands with greater force than does air, but strictly speaking, it is not a requirement.
While what you say is true, it is the difference in force between heating air and heating water (expansion of volume) that causes water to generate enough pressure to maintain the water in the upper globe from draining back down.
JPDyson Said:
That is to say, air alone will expand with heat (go fill a balloon and microwave it for proof). However, it occurs to me that you couldn't totally eliminate water anyway. There would need to be a gap for the purpose of transfer, which means there will necessarily be an amount of water remaining. I guess the important question is "why so much"? Why not an 1/8th inch gap - surely vapor could pass if the gap were that small. Would that have a detrimental impact on the amount of pressure in the system?
The second half of the equation, which has been covered above my posts is that you do not want to over heat the glass, as long as there is water in the bottom, it will not get hotter than the boiling point of water at whatever altitude you are at. Yes it will be slightly warmer on a technical point but the change state of water to steam acts as a temp moderator and dispersion on the bottom globe. If all the water were to boil out, you would have hot spots in the glass, uneven heat, hot spots, different expansion in different places of the bottom globe, stress and eventual breakage of the bottom globe.
A 1/4 inch of water on the bottom is nothing in the real evaluation of things and is easily absorbed into the brewed coffee.
In real life, my name is Wayne P.
Feed the newbs, starve the trolls and above all enjoy what you drink!
Thanks for the information....could you give me a detailed instruction as to how to use it, I haven't been successful in making decent coffee. Perhaps it only works well if you make a full pot...I was hoping I could make as little as 2 cups but with about 1 cup of water remaining in the botom vessel it doesn't work that well. The siphon tube "ends" about 1 inch above the bottom of the lower vessel, leaving about a cup of water.
Yes - you have thought out the answer for yourself - vacuum pots definitely work best if you use them for their design capacity. Anything significantly less - and it sounds like that is happening in your case - unfortunately doesn't turn out well.
Manufacturers make them from a 2 cup size up to a couple of litres for that reason.
Warning - collecting them in different sizes can get obsessive as I have discovered, but they do all get used according to the amount of coffee needed.
Indeed, a full pot is nearly always recommended. I have no personal experience brewing less than a full "6 cups" in mine, which works out to two good mugs.
As for detailed instructions, you know what they say about teaching a man to fish... this very site has a really nice write-up by Mark on vacuum pot coffee, and there's always brewmethods.com to check (though, they tend to offer a variety of approaches and leave you to decide which is best). Here's how I do it, based on various tips and experience. I don't mind sharing it since I'm one of the few, the proud, the electric stove vacuum brewers! I do not use the wire trivet that came with the pot, and have never had any trouble.
600g of water (heat 700+, as there's a little needed for rinsing). I'm scary good and eyeballing 750mL in my Hario. 40g coffee (this is an up-dose, but I find it works best for me)
-Pre-heat the water in a kettle to 205F -Loosely assemble the pot, and pour a little water over the filter (mine is cloth, but I still rinse it) -Swirl the hot water around the lower pot and then discard -Pour 600g of hot water into the lower pot, and apply heat (about a '6' on my electric stove) -Affix the upper bowl, and allow water to rise completely AND reach brew temp (depending on the coffee, I start at 195-200F, and it will surf up to 205F max) -Reduce heat to about a '3.5' (sometimes a 3 if I start higher, like 200F) -Grind the coffee (setting about 16 on my Virtuoso, which is coarser than one-cup pour-over for me) -Dump the coffee in and give a quick stir to saturate. Start a 2 minute timer. -Stir again at 1 minute. -Remove from heat at 2 minutes. *Now, confession: at this point I start blowing on the lower globe to aid in cooling, but I stop short of applying a cold towel - I find that to be a bit too aggressive for my sensibilities. Not that I've personally seen it cause an implosion, but I don't want to risk it. I can transition from brew to kick-down in 15 seconds just by blowing across the lower pot* -Brew is finished between 3:15 and 3:30
This method produces a cup that has a certain richness and presence that is lacking in my pour-over cups (but not quite that of a french press) but still clean. Tasting notes are typically prominent but balanced (certain notes are 'sharper' in a pour-over, whereas this vac-pot method has a certain mellowing affect). I can't even stand to take a sip for the first 3-4 minutes (coffee comes out screaming hot).
This Silex of yours - is it stove top, or did it have its own heating base?
Very nice write-up, indeed. [As I sip a lovely City+ El Salvador brewed in my Yama vacpot an hour ago]
Two minor points to add:
+ I replaced the cloth filter/spring assembly in my 5 cup Yama stovetop vacpot with a glass Cory rod from eBay ($7, I think). I am told, and my experience supports, that a Cory rod can be an add-on to just about any vacpot. The result is no cloth filter maintenance or cleaning. The taste is remarkable--the fullness of a press pot with nearly zero fines at all. Just don't whack the Cory rod what you stir the grounds in the upper vessel. For clean up, a quick hot water rinse and bottle brush, and then into the dishwasher 2x per week, or so.
+ Once the water has migrated north into the upper vessel, maintain a fair amount of bubbling and gurgling. Don't turn down the heat so low that the bubbles up stop or slow down (don't worry, you won't run out of air from below). This, as you would imagine, increases the strength of the vacuum and the draw-down and reduces the risk of a stall. In addition, I like to bubbles and gurgles for some turbulence during the brew time.
If you do stall (i.e. the draw-down doesn't start within 20-30 seconds and finish within 60 secs), then likely causes are (i) you've lost the vacuum (shifted seal, or cracked seal), (ii) not enough air migrating upward during the brew time, or (iii) Coffee grind is too fine. Most often, it's that the grind is too fine. This is especially the case if you are using a Cory rod vs. a cloth filter.
I too use a Virtuoso grinder, like JPDyson, however I push the grind a touch finer. However, on a darker roast the brew can sometimes stall because the grind contains just a little more fines and powder that can clog a Cory rod. If you are using a cloth filter, you can have more flexibility.
Stick with it until you work out your personal recipe and procedure. Vac pot is such a wonderful way to showcase a great coffee.
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