# Looking for Headspace vs Beer CO2 Calculation

### Help Support Homebrew Talk:

#### Vale71

##### Well-Known Member
One more thing you can simulate with the spreadsheet is the drop in pressure you'd get if you were to seal your FV and then cold crash it without attaching a CO2 source and then waiting long enough for beer to start absorbing more than a trivial amount of CO2. Just set the temperature to your fermentation temperature and your manometer pressure to zero.

With 20% headspace cooling from 20°C to 0°C you'd end up with a whopping -0.44 bar of vacuum, more than enough to seriously damage your fermenter. A surprisingly small amount of CO2 has to transfer to the beer for that to happen (unless you brew in the 100bbl range, of course).

OP

#### VikeMan

##### It ain't all burritos and strippers, my friend.
Added a "Pressure" column to the table that lets you see at a glance how pressure in your vessel will change with temperature once the new equilibrium is reached.
@Vale71 I've been playing with your spreadsheet. Pretty cool! When the value in the pressure column (call it "P") goes negative (for lower temps), what does that mean? That the gauge would read zero and that the Actual Pressure (not gauge) in BAR would be something like 1 Atmosphere minus (-1 x P)? Thanks in advance!

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#### Vale71

##### Well-Known Member
That is indeed correct. I've set the formulas to give what a manometer would read, so relative to atmospheric pressure (rounded to 1 bar for simplicity ) and not absolute.