Aeration and Oxidation
Oxygen is a vital component for good yeast growth and propagation. Unfortunately, just as it is good for yeast, it is very bad for wort. Oxygen in the wort can lead to off flavors such as cardboard and sherry. So how do you go about adding oxygen to your beer without causing issues with oxidation? First you want to make sure that you cool your wort to below 80 F prior to aerating to avoid what is referred to as “Hot Side Aeration”. There is much debate as to weather this can truly cause oxidation flavors within the wort, but for best practices we recommend cooling the wort prior to transferring. Next you want to go ahead and aerate your wort in your fermenter.
There are several ways in which you can go about aerating your wort. Splashing is probably the most simplistic way of aerating. When transferring to your carboy, pour the wort between two vessels so that it splashes around. Although this can be quite effective, there is a slight risk of contamination via airborne particles. Another way to effectively aerate and probably the most popular among homebrewers is agitation. After the wort has been transferred to the fermenter, you can rock the vessel back and forth for a few minutes. Please take caution if you are using a glass carboy by putting it on a padded surface and hold tightly to ensure that you not crack or damage the fermenter. The last and probably most effective way to aerate your wort is to inject air or pure oxygen. Although for this method you will need some additional equipment. To inject air into the wort, one of the easiest and least expensive ways to accomplish this is by utilizing a simple aquarium pump. This can be hooked up to a tube with a HEPA filter. The air is then pushed through a diffusion stone which makes very tiny bubbles and increases the gas to liquid surface area. If you were to try to inject air without the use of a diffusion stone it would not be effective as the bubbles would be too large and will just float to the top and gas out. It is recommended that you let the air push into the wort for approximately 15-30 minutes to ensure that there is enough oxygen present for the yeast. Pure oxygen can also be used to aerate your wort by using a disposable oxygen tank found at many home improvement stores as well as an oxygen regulator. You can use the same basic setup as you did with aquarium pump but you will not need a HEPA filter when using pure oxygen. In addition, since you are using pure oxygen and not air, which only has about 21% oxygen, you will only need to aerate for approximately 1 minute. Please be cautious when using oxygen as it is extremely flammable, so do not use around any heat or fire source.
Now you can go ahead and pitch your yeast, once your yeast has been pitched you do not want to add any additional oxygen or air to the wort as it can cause off flavors in your beer.