Aeration By: Kay Witkiewicz
Just like you and I, yeast needs to breathe in order to survive. Although oxygen is a dirty word throughout most of the brewing process, it is one of the main determinants that influences the health of your fermentation and ultimately the taste of your beer. On a biochemical level, yeast requires oxygen to reproduce viable and vital cells, while the timing and method of aeration have significant effects on the dissolution of oxygen in your wort. As with numerous other aspects of the brewing process, aeration is a small but essential step that can make the difference between good and great homebrew.
Your yeast demands oxygen for the production of sterols and unsaturated fatty acids (UFAs), which are integral components of the lipid bilayer of yeast cell membranes. Sterols and UFAs keep the membrane permeable, flexible, and healthy to ensure efficient exchange of nutrients, metabolic transfer of sugars into the cell and alcohol out of the cell, and seamless budding of new yeast cells. Budding is the process by which yeast cells clone themselves and the aforementioned compounds make sure that each offspring is a perfectly vibrant replica of its parent cell. Think of budding like taking a big ball of pizza dough and dividing it into multiple little dough balls: the water and flour you are likely to use to cleave, shape, and smooth your bits of dough are akin to the roles sterols and UFAs play in yeast reproduction. Just like a perfect little dough ball will make for a crunchy crust and great pizza, a perfectly budded yeast cell will make for a healthy fermentation and great beer.
Temperature determines when to aerate your wort. The solubility of oxygen decreases as temperature increases, which is one of the reasons why your wort is susceptible to the deteriorating effects of oxidation during your mash but not during your boil. Rapid chilling of your wort further minimizes oxidation and exposure to harmful organisms. Although the general guideline holds that it is ok to aerate your wort at any temperature as long as it is below 80-degrees Fahrenheit, I prefer and recommend the low 60-degree range because it is easier to dissolve oxygen as temperature decreases and in the interest of a healthy fermentation it is preferable to pitch your yeast a few degrees below its recommended fermentation range and then let it rise naturally to its optimal temperature, which more than likely will be between 60 and 70 degrees Fahrenheit. A speedy and precise chill of your wort will minimize oxidation and infection and maximize your wort’s aeration potential.
Plenty of madness pervades the methods you can use to aerate your wort. I prefer the traditional splashing technique by pouring my wort back and forth between my brew kettle and my bottling bucket, alternately placing a sieve over each in order to catch my hops and trub. After pouring it back and forth at least a half-dozen times, I then splash my wort from the bottling bucket into my carboy with the help of a funnel, pitching my yeast about half-way through the process. So far, this method has worked great for my beers (OG mostly between 1.060 and 1.080) and I imagine you could achieve the same results with a little less labor by using a siphon sprayer. For the more sophisticated homebrewer, an aquarium pump and a sintered stone or even a direct infusion of pure oxygen represent more efficient methods of aeration. I’m considering upgrading my aeration process to one of these two ways in order to ensure that my higher gravity brews (OG above 1.080) have enough dissolved oxygen for the yeast to work its magic cleanly and healthily. The higher the gravity of your beer, the higher the number of yeast cells needed during fermentation and, consequently, the higher the oxygen requirement. Regardless of your method of aeration, it is extremely hard to accurately measure the amount of oxygen dissolved in your wort. Using the old splashing technique is the least accurate of the bunch, whereas you can easier estimate and more consistently maintain the same flow rate for the aquarium pump or pure oxygen infusions. Your method of aeration and your results will vary depending on your brewing system, so trust your palate when analyzing your final brew and if you detect any prominent fusel alcohols or other off-flavors related to aeration, then reconsider your current practice in favor of making better beer in the future.
Oxygen is a necessary component of brewing beer when introduced in the right amount at the right time. Yeast cells utilize oxygen to reproduce healthy offspring that allow for efficient exchange of nutrients and transformation of sugars into alcohol during fermentation. The temperature of your wort will dictate when to aerate since the colder the liquid, the easier it will be to dissolve oxygen in it. The way you aerate your wort will depend on your homebrewing set-up and whether you do it old-school or high-tech, as long as your beers emerge as tasty as you want them to, stick with your preferred method. Oxygen is as vital to our wellbeing as it is to the lifecycle of your yeast and the taste of your beer, so cherish aerating your wort as much as you cherish breathing.