# Negative Pressure



## Ben Brewcat (Oct 27, 2004)

Could well be negative without a failure in the vessel. Imagine a finished mead, at neutral pressure. Then a high-pressure front (say, oh, I don't know, an arctic cold front in Kansas ) comes in. The high pressure outside the vessel makes the airlock lean "in" as it tries to equalize. This phenomenon is the reason for topping up carboys for extended aging; less airspace minimizes the effect.

Big bummer about that leaker mead though.


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## Aspera (Aug 1, 2005)

The most likely explanation is that you have a first hand observation of Boil's gas laws. As the temperature of the fermentation vessel decreases, so does the pressure of a gas in a fixed volume vessel. It only takes a degree or two to affect an airlock. As Ben says, liquids are less subject to such effects, so minimizing headspace can will help your cause.


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## nursebee (Sep 29, 2003)

Try vodka next time. It won't flavor things as much.
I've done some mineral oil on top of vodka to minimze evaporation, wow is that a PITA if it gets in the mead.


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## Ben Brewcat (Oct 27, 2004)

Believe it or not some books recommend a layer of mineral oil over a wine or mead to guard it. What an amazing hassle that must be!


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## chemistbert (Mar 4, 2004)

Get a few of the silicon stoppers with the little flap on them that acts as a one way valve for your carboys. I have a mead that's been aging for over a year and don't hardly ever look at it. They are well worth the five bucks they cost.

Part number 7953
http://www.northernbrewer.com/ferment.html

They rock!


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## Ben Brewcat (Oct 27, 2004)

Hunh. That's cool.


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