Hop Plugs (properly T100 pellets) were developed to go through the bung hole (where the Shive goes) of a cask and they were left there for the full life of the beer.
Note that they were serving with gravity or at most the small suction head of a hand pull pump and that the keg tap (or Spigot) has a strainer built in. Applies to wooden, metal and plastic spigots.
Hop Plugs a basically whole hops pressed into a 1/2oz lump, so they are going to be a lot easier to strain out than is hop powder which is what T90 pellets are made of.
Given the higher pressure applied in kegged over casked beer and the much finer hop product we mostly use, I find dry hopping in the keg to be a real PITA unless you bag/ball or otherwise contain the hops. Had more than one tap/line/disconnect/keg post... blocked solid.
I find it only takes at most a couple of days to get all the benefits from keg hops so I normally use a hop bag and pressure transfer the beer from one keg to another after a week or so, all the benefits without the problems from loose hops.
I also find that hopping late gives a slightly different flavour/aroma to hopping early, I suspect its the lower pH which affects the solubility of some products. The presence of more alcohol, alcohol is a pretty potent solvent, will also change what goes into solution. I think maybe the carbonic acid formed from increased CO2 in solution may have some impact to, CO2 can be a good solvent to.
Mark
