Hey guys,
I have a physics question: you're told not to close a glass carboy while cold crashing or the carboy will implode.
I saw that you can use an extra long blowoff tube so the suckbacked Star San doesn't make it's way all the way back to the carboy. But wouldn't that extra CO2 in the tube that gets sucked back do the exact same than sealing it completely off?
No, the "sucked back" CO2 makes up for the drop in internal pressure caused by the drop in temperature. The gas law is PV = nRT, where P = absolute (not gauge) pressure, V = volume, n = the number of gas molecules, and T is temperature (measured on a absolute scale) and R is a universal constant. For a sealed container, V, n and R are all constant, so if T goes down, P must also go down. If you can suck back CO2, then "n" is no longer constant, so the pressure will not drop as much. In fact for typical blow off geometries, the pressure difference between the inside of the carboy, and the outside atmosphere will be much less than 1 psi. So, without the pressure differential, the implosion risk goes away.
Brew on
