Beerbeque

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I racked my ~100f wort into a carboy, capped it and put it into my fermentation fridge to finish cooling so I could pitch my yeast the next morning. When I uncapped the carboy there was a vacuum inside
so it naturally sucked in a lot of air. Does anyone know what caused this vacuum?

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Misplaced_Canuck

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100F air+wort that has dropped to 70F will definitely create a partial vacuum.

M_C

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Originally Posted by Unknown Carbonic bite? Is that like the bubonic plague?

Homercidal

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The density of a liquid decreases as it's temperature rises. Therefore it's volume increases.

Likewise, as a liquid cools, it becomes denser, therefore it's volume decreases.

Your wort shrank.

Revvy

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That's what no-chill brewers do to help insure that nothing nasty gets into their aquatainers. As the fermenter cools what was expanded contracts, both the molecules in the liquid, and the surround air. Causing a vacuum. Same principle as when folks can.

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Misplaced_Canuck

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And air.

M_C

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Quote:

Originally Posted by Unknown Carbonic bite? Is that like the bubonic plague?

xjmox14x

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This really has nothing to do with the wort. Yes, the water does contract some, but the amount is really moot compared to the change in pressure due to the air temperature decreasing.

What you are describing is the Ideal Gas Law. Although air is not an ideal gas, it is a good approximation for most gases (i.e. the air inside your carboy).

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ajdelange

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Just remember "pervert equals nert". It even rhymes. This silly, but handy mnemonic is for

P*V = n*R*T

which, dividing both sides by volume results in

P = n*R*T/V

IOW for a fixed amount (n) of a gas confined to a fixed volume (V) the pressure is proportional to the temperature (R is the proportionality constant). Thus, cool the gas, the pressure drops. That's responsible for most of the pressure drop. In cooling from 40 °C to 10 °C the pressure of a gas drops about 10%. The rest comes from the shrinkage of the wort as it cools. In going from 40 °C to 10 °C the volume of 10 °P wort decreases approximately 0.76%. If the carboy were half full this would cause a pressure drop of about the same amount i.e. 0.76%. For 2/3 full carboy it would be about twice this and so on.

solbes

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It'll happen every time. Pressure of the "air" decreases with reduced temperature.

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day_trippr

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How does creating a vacuum within a wort bag insure nothing nasty gets in? That's just the opposite from how a bio-lab works, for instance, where a positive pressure is maintained within the lab.

Always suspected those no-chillerz were a bit loopy

Cheers!

FoundlingOfDollar

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In a lab setting the lab is positively pressurized because the room may/will leak. No chill brewers are assuming that the container will remain airtight. The wort goes while still boiling thus sanitizing the container and hopefully any air in the headspace (no chill brewers typically try to minimize the amount of air in the container by squeezing it before closing it). The vacuum minimizes contact with the air that was already in the container, and the smaller volume of air inside the container is more easily heated by wort and steam, thus keeping things from getting into the beer from the air in the container headspace, rather than from the outside.