Home Brewing and Oxygen
Recently one of the things I have been focusing on with my beer making is fermentation practices. For a while now I have been using a temperature controlled fermentation chamber and yeast starters to make sure that I had sufficient quantities of yeast and an ideal environment for the yeast to ferment in. That being said, I have been pretty relaxed when it comes to oxygen levels and have been working on making progress in that area.
Just some basic information on oxygen and home beer brewing. At certain points in the beer brewing / beer fermentation process, oxygen can be either your best friend or your worst enemy and it is important to know when to add and when to avoid it. Thankfully it is pretty easy to keep track of! The only time that you want to introduce oxygen to your beer is post boil and once the wort has cooled down and you are preparing to pitch your yeast. The reason for this is that yeast requires oxygen for healthy propagation. “Yeast use oxygen for cell membrane synthesis. Without oxygen, cell growth will be extremely limited. Yeast can only produce sterols and certain unsaturated fatty acids necessary for cell growth in the presence of oxygen. Inadequate oxygenation will lead to inadequate yeast growth. Inadequate yeast growth can cause poor attenuation, inconsistent or long fermentations, production of undesirable flavor and aroma compounds, and produces yeast that are not fit for harvesting and re-pitching.” – Wyeast Labs. During the boil process, much of the oxygen is stripped away from the wort, so it is good practice to reintroduce oxygen back into the wort. There are several ways to accomplish this but the key is to do it in a sanitary way. Many brewers will rapidly stir the wort or swish it around in the fermenter and others will pump pure oxygen into the fermenter with a diffuser stone. In my setup I keep the yeast oxygenation / aeration process pretty simple and meet in the middle. I use an aquarium pump with a stainless steel diffuser for about 15 minutes once I have transferred my wort to the fermenter. It has an inline HEPA filter to make sure I am not blowing a bunch of dust or wild yeast into my wort. I also pitch the yeast at the same time. You can pickup at yeast aeration kit from MoreBeer.com for about $35.
Once you have aerated your wort and begun the fermentation process you will want to do everything you can to avoid introducing oxygen into your beer. Thankfully, the yeast will help you with this process. As the yeast consumes the oxygen to replicate itself and converts the sugar in your beer, it is creating two main byproducts which are alcohol and CO2. The creation of the CO2 will help purge any residual oxygen from the fermenter. The next step is doing your best to avoid introducing oxygen to your beer when it comes time to transfer your beer to the keg. The most common way to do so is to purge your keg with CO2 from a CO2 tank and then push your beer from the fermenter with CO2 from a CO2 tank. In my setup the only thing that I do differently is that I use the CO2 being expelled from my fermenter during active fermentation to purge my keg. You can view the setup in the photo at the top of this article to get a visual, but basically I am diverting the CO2 to the keg as opposed to pushing it the a flask filled with sanitizer. I user mini stainless steel ball lock valves that I picked up here from Amazon. For the final step, I push CO2 into my fermenter to build about 3 PSI of pressure and move the fermented beer from the fermenter to the keg as shown in the following image.