Getting ready to keg for first time

I've never purged before and I usually forget to purge afterwards. I can't say I've ever really noticed any problems with any of my beers.

 

Remove the oxygen as best as a homebrewer can. Oxidized beer is (most likely) a characteristic you did not design your beer to have. CO2 is heavier than oxygen so when you "purge" you are creating a buffer between beer and oxygen, as you fill the keg (WITH THE PRESSURE RELIEF VALVE OPEN) the CO2 will sit atop beer and push oxygen out as beer comes in. Purging the head space is the same idea.

 

Si. Air is now your enemy. Purging with CO2 is an extra step to minimize contact with oxygen. As you noted, if your keg is full of air the beer will displace the air (or CO2 if you purged) as it fills. Then a series of burbs and the keg should be oxygen free.

My technique is to put some starsan in the keg under pressure. Give it a good shake/rinse and force the starsan out with CO2 (rinses inside of dip tube). This mini-flush will reduce the air . . . but a few molecules of oxygen probably make it through so I still burb it. If you are paranoid you can completely fill keg with water and push it out . . . should be CO2 only remaining.

Also, consider adding your beer through the liquid outpost. Once you have purged you leave the lid sealed (with PRV open) so less air intermingling with the headspace. In theory more sanitary and less splashing.

As a minimum you want to do several "burbs". Carbon dioxide is your new friend.

 

My first kegging adventure, I opened the lid and dropped the tube down to the bottom from my auto-siphon. The beer tasted just fine, but it got extremely oxidized (it was a hoppy amber that looked like a Moose Drool once I started pouring from the keg). So my next attempt (and standard for all hoppy beers from now on) is to ferment in bucket with a spigot (many homebrewers refer to this as the bottling bucket), the trub sits below the spigot for the most part. I have a liquid ball lock disconnect connected to some siphon hose that fits right over the spigot.
Purge keg with CO2 through the out-post. Connect siphon hose to spigot and liquid ball lock disconnect to out-post. Open spigot and open pressure relief valve. Clear beer gently rolls into the keg from the bottom. Once the flow stops, I call it good and live with the last 1/2 gallon left above the trub.
ONE IMPORTANT THING TO REMEMBER (mistake I made): I purged the keg of CO2, connected my siphon hose and liquid disconnect to outpost and took the airlock out of the lid of my fermenter. I FORGOT TO OPEN THE PRESSURE RELIEF VALVE and the CO2 found the easiest path to atmosphere through the out-post up the siphon hose into the fermenter and through my beer. OPEN THE RELIEF VALVE WHEN TRANSFERRING.

 

When I clean a keg
1) Circulate oxyclean with a homemade keg cleaner, then push the oxyclean out the "out tube" with CO2.
2) Rinse with hot water and push that out with CO2
3) Add a bit of StarSan and shake the keg and then push out with CO2. I leave a little bit of starsan in the keg under pressure.

When I go to fill a keg, I release the pressure and fill through the lid on top of the CO2 that is still in the keg. If the keg is not still pressurized, I assume that it is not sanitized and it goes back in the "to be cleaned" stack.