He said "oxygen." When you have liquid in the PET bottle you can squeeze all the air out before capping it with the carbonator, then add CO2, but with hops, I don't think you can do that, so there will be some O2 in there, but very little.
So, how does the oxygen that is in there get purged?
like any standard pin lock - depressing the poppit in the middle.
I have always assumed that the idea is to fill the container with co2, wait a bit for things to settle down in there and then purge through a top opening which should get most of the o2 out as it will have migrated to the top portion of the container. still some o2 but a lot less
That's not how gases work. Otherwise, basements would be deadly. :-)
excuse me, let me add 'In absence of any continued mixing' which, for all practical purposes doesn't happen in 'the real world'. and basements CAN be deadly. Think co2 fire extinguishers, or failing co2 bulk tanks for that matter. If you are in a basement with say 500lb of co2 in a tank and that tank suddenly empties that basement will very much be deadly. Why? because the co2 will displace all the other gases from the bottom up. That's why it works to put out fires. that's why a balloon filled with helium rises. That's why the myth buster guys can do the trick with the heavier than air gas in the fishtank and the boat made of foil (look it up, it's pretty cool). It's not perfect statification and any little tiny movement will mix the gases again but it does happen.