I bought a king keg off a 'seasoned' brewer who warned me against half filling a keg and half bottling as it means the keg would have more oxygen in to damage the beer. However wouldn't the gas you put in the top form a protective layer and hence stop oxidisation? Obviously if you transport it somewhere or otherwise shake it up it would be exposed to the oxygen, but if I'm doing that then I'm assuming it will be drunk fairly quickly...
Any thoughts?
Any thoughts?