What caused the vacuum in my carboy?

[Beerbeque]

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?

 

[Misplaced_Canuck]

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?

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

M_C

 

[Homercidal]

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]

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.

 

[Misplaced_Canuck]

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.

And air.

M_C

 

[xjmox14x]

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.

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).

 

[ajdelange]

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]

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

 

[day_trippr]

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.

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]

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!

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.

 

[Cryptochronolite]

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?

While I agree with all the temperature information, I think one key that we should remember that any water vapor remaining from the latent heat of the boil will condense to 1/1600th of it's size as it undergoes the phase transition from steam to water.
Although a temperature decrease of the hot air in the carboy causes this, I believe the condensation of water vapor has most to do with the vacuum rather than just the cooling of hotter air.

 

[day_trippr]

[...]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.

Ah, it's more of an interior sterilization thing.

Thanks for the clarification, that's quite a bit different from "nothing nasty gets into their aquatainers"...

Cheers!

 

[ajdelange]

I believe the condensation of water vapor has most to do with the vacuum rather than just the cooling of hotter air.

Good thought and its effect could be bigger than wort shrinkage (with large headspace) but it wouldn't be as big as the cooling effect. This is because at 40 °C (104 °F) water vapor molecules are only 7% of the total and at 10 °C they are 1%. Thus in cooling from 40 ° to 10 ° the vapor pressure of water changes from 55 to 9 i.e. a pressure drop of 46 mmHg. The pressure drop from just the temperature drop per the gas law is about 76 mm Hg.

 

[Cryptochronolite]

This is because at 40 °C (104 °F) water vapor molecules are only 7% of the total and at 10 °C they are 1%.

I didn't see his measurements on humidity/partial pressure/etc, where did you get those numbers?

 

[ajdelange]

No need for measurement of anything other than temperature. The vapor pressure of water over water at 100 °C is 760 mmHg (it boils at 1 atm). The vapor pressure of water over water at 40 °C is 55 mmHg etc. The data can be found in any of several handbooks or calculated from a polynomial in °C whose coefficients are
{4.56600473900825,0.357517244572698,0.0054215635187451,0.000648616184567133,-1.66197374603959e-05,4.47816322822026e-07,-5.43174883854266e-09,3.60481016695178e-11,-9.72090405360733e-14}

In the case of wort the pressures would be a little (very little) less than for pure water as the mole fraction of water is less than 1 in wort.

Given that the initial pressure (i.e. when he sealed the thing up) was 760 mmHg the partial pressure of water of 55 mmHg implies that 55/760ths of the molecules (about 7%) in the head space are water vapor. At the lower temperature 9 mmHg would be 1% (approximately) on a base of 760 but as the total pressure at 10 would be lower than 760 the percentage water vapor would actually be a bit higher than 1%.