In beermaking it is critical that you limit the beer’s exposure to oxygen. Oxygen can react with compounds in the beer to degrade the overall quality of the brew but perhaps most noticeably it can create undesirable flavors. However, exposing wort to oxygen is a whole different story. In fact, prior to pitching the yeast, you’ll actually want to make sure that there’s a certain amount of oxygen in the wort. Having oxygen in the wort will make for healthier yeast, better attenuation and an overall more complete fermentation.
It is important to note that you’ll only want to introduce oxygen to wort that has been properly cooled. Bringing oxygen into the mix with wort that is hot or warm will inhibit bacterial growth ultimately increasing the likelihood of infecting your beer. You should always make sure that you are cooling the wort to pitching temperature immediately after the boil is complete and before aeration.
There are a number of ways to introduce oxygen to wort but they all fall under two main approaches: aeration and oxygenation. Aeration is the process of adding air to the mix while oxygenation is the process of infusing pure oxygen.
The difference here is that air is only about 20% oxygen. Because of the difference in composition, using pure oxygen will be the quicker approach though aeration can get the job done just as effectively.