[Homeroast] Hybrid vac pots--blowing off steam

Samuel Goldberger sgold at sphere.bz
Mon Apr 5 03:28:00 CDT 2010


Ray's expostulations are always cryptic, sometimes witty, but usually correct in the main. This time, however, 
some comments seem needed. 

On Apr 4, 2010, at 3:19 PM, raymanowen at gmail.com wrote:

> Vacuum brewers are designed to draw hot water up the stem into the funnel
> with the Foulgers.

/flame on

As always, Ray, quite witty. Presumably, however, you meant Folgers, or more precisely ground coffee. 
However, this statement is very misleading. Vacuum brewers are designed to allow the expanding water
 to *rise up* the stem into the funnel. There is no "drawing" except when the bottom cools down and the 
brewed coffee is *drawn* by the vacuum that results. 

If you are trying to clarify a technical point, it helps to be somewhat accurate in your language. Otherwise, you appear 
to be whistling up the windpipe, or should I say "drawing up the windpipe?"	Surely you wouldn't want that. 

> A layer of water has to remain on the bottom of the pot,
> so the glass never exceeds the boiling point of water.

No, it doesn't *have* to (see below), though every vacuum pot I have used (some 10-12) does allow some water to remain in the bottom.
That's because if the stem reached the bottom of the lower vessel, the water wouldn't rise all the way up to the funnel. However, 
the stem could be quite short, and the water would stlll rise through it because it has to go somewhere when heating to boiling.

> 
> If the stem is forced deeper into the pot to draw up more water, the thin
> layer of water will boil away completely in a few seconds.

Actually, the amount of water that rises up the stem is not so much dependent upon the depth or the length of the stem as it is by the length of time the heat is applied 
to the bottom vessel. 

> The borosilicate
> glass can withstand the soaring temperature, not the sudden inrush of cooler
> coffee (~200° F coffee Vs 300+° F) on the boiled-dry glass bottom.

That supposes that the heat is left on during brewing. But that would make for very lousy coffee; and the water would never descend. 

In fact, this descent comes about precisely because the lower vessel begins to cool, which in turn requires that the heat be removed.
This is generally after 2-3 minutes or more of cooling. The cooling creates a vacuum (hence the name). 

By that time, even an overheated glass vessel would generally have cooled sufficiently to withstand the descending coffee. 
You wouldn't by any chance be resolving a non-existent problem, would you?

> 
> Some have imagined "excessive vacuum" caused the pot to shatter. News Flash-
> No!

Who exactly are those imagining this, Ray? Are they friends of yours? Or is this a further straw-man argument?

It's extremely hard to get even an old glass vacuum pot to shatter. I have some dating back to the 30's and '40's
made of early versions of Pyrex. They are very heat resistant, and have been in service for over 60 years. 
In the unlikely event that a pot does shatter, it's most likely because the glass had a stress fracture, not from heat but from impact. 

> If you're not using the *exact* funnel-gasket-pot  components in the vac
> pot, a GI party could be in your future.

My, how we love our abbreviations. But whatever a GI party is, the issue has little or nothing to do with exactness of 
components (though if you don't get a good seal you won't get a vacuum, and hence no coffee), and everything to do
with the application of heat. It is very hard to draw correct conclusions from false assumptions. 

> 
> (My last GI party was interlaced with San Miguel and involved policing
> cigarette butts outside the 1st Mob maintenance shop at Clark.)

I am sure you know precisely what this means, and it's extremely amusing, and ultra macho to boot.
It sure puts us wimpy non-smoking non-vet home roasters to shame.

Thank you for the self-revelation and military reminiscence. It contributes enormously to our 
understanding, and you do appear to be a lovable old curmudgeon, even if you don't understand 
vacuum pots. But you certainly are an expert roaster, or so you always tell us, and your wife
agrees. Who then could disagree, much less challenge you? 

> 
> Cheers, Mabuhay -RayO, aka Opa!
> -- 
> Persist in old ways; expect new results - suborn Insanity...

Sounds both wise and witty. However, by persisting in old ways, one often improves one's skill set, and thus obtains new results.
Or, situations change in such a manner that the old ways do in fact produce new results, as is the case with home roasting. 
Even bad habits are not in themselves insanity. They are bad habits. 

/flame off





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