I watched a brewer vigorously churn his near boiling hot wort (insert and raise the wort chiller (copper coil) repeated times to crash the temperature from the boil down to near pitching temperatures... think churning butter image, that is what he was doing. Also watched as he transferred from primary to secondary with the hose a foot off the bottom of the vessel being transferred into. I expect the same happens when he transfers into the serving keg. Then his practice (like many of us) is to force carbonate his kegs with 40 psi and shaking the hell out of the keg. My guess is that he never purges the air out of the keg with C02 before the shaking of the keg.
All of these errors in practice will oxidize your beer. He asked me why all his beers seem to have a distinctively similar taste...oxidation. Just those sloppy practices is all it takes to ruin a likely good batch of beer.
