One of the bugaboos of my brewing has been oxidation, a papery flavor that develops after the beer has been packaged. Oxidation alters the flavor of the beer over time, reducing its shelf life, but in extreme cases it can start adversely affecting the beer very quickly. I’m not talking about hot-side oxidation, that’s been debunked as a factor in beer flavor. I’m talking about any introduction of oxygen into the beer after yeast has been pitched.
Oxygen is vital to fermentation, at least initially. I’ve read of some experiments in low-oxygen fermentation but I’m not quite ready to throw out years of brewing experience based on a few experimental runs using various oils as the source of sterols for yeast cell walls. The problems occur if oxygen is introduced after fermentation is underway. The compound responsible for the papery flavors can be detected at concentrations less than a part per billion so only a little can adversely affect beer.
As I write, I’m sipping a beer brewed October 4th of last year. It’s April 18th: The beer is six months old. I can detect few signs of aging in it. About the time of this brew, I got a CO2 tank and began sparging the vessels before transferring beer into them. In fact, the beer tastes as good as when I bottled it. By layering a bit of CO2 in the carboys before racking, I limited the amount of oxygen introduced to the finished beer. It worked, as near as I can tell. My beers no longer show signs of oxidations, not this nor any of the subsequent brews.
If you can’t afford to go out and buy a carbon dioxide tank and regulator, you can still get some benefits by limiting handling of the finished beer. If you can avoid racking the beer, you eliminate one possibility to introduce oxygen. If you have access to another inert gas and can sparge with it, that will work as well. At least limt flow from the racking cane until the tube is below the level of the beer to limit splashing. Bottom line, keep oxygen out of your beer. It will taste better longer.