Last hoppy brew I made I used the method where you purge the keg of oxygen by pushing starsan out before you fill through the liquid post. It worked great and I've been really happy with that beer.
Now I want to do it again but this time I also want to keg hop an NEIPA for extra aroma.
My question is do people add their hop bag (or in my case steel mesh tube) to the keg with the starsan in it?
This is the missing piece of the puzzle for me. How can you dry hop without adding O2? The way I see it, there are several options but none are perfect.
1) Don't purge keg, rack to the keg, add hops, purge several times
2) Purge the keg of star san, rack to the keg, open quickly to add hops, purge several times
3) Don't purge keg, add hops to keg, purge several times, rack to keg, purge several times
4) Purge the keg of star san, open quickly to add hops, rack to keg, purge several times
I guess the big question is how much O2 gets in when you pop open the lid to add hops. I don't know and modeling it mathematically is probably and effort in futility. Too many variables and assumptions.
I've read on this site that some people will purge the keg and then hook up the CO2 to the liquid out post. turn it on a really slow trickle of gas, open the lid, add hops, close lid. Their hope is that the positive pressure from the CO2 tank into the keg will prevent O2 from coming in the open lid.
What I've been doing lately is to rack to a dry hop keg while fermentation is still active but almost done (maybe day 4). Add hops. Close up the keg, purge several times. Then hook up a blowoff tube so that the continuing fermentation will hopefully push out the remaining O2 that I didn't purge out. This isn't an ideal method either but I figure it doesn't waste a lot of CO2 and probably purges the keg as well as any other method. After a 1-2 days, I put on spunding valve to start building up pressure in the keg.
