Oxidation is a chemical reaction that occurs when a substance reacts with oxygen. It is a process where atoms or molecules lose electrons to oxygen or other oxidizing agents. This reaction can alter the chemical composition and properties of the substance. It is important to avoid oxygen exposure during beer fermentation. When oxygen comes in contact with fermenting or fermented beer it can cause several negative effects including negative impacts on the quality and flavor of the beer. Here are a few reasons why oxygen should be minimized during fermentation:
1. Off-flavors: Oxygen can react with the compounds in beer, leading to the development of off-flavors. This is particularly true during fermentation when the yeast is actively converting sugars into alcohol. Oxidation reactions can produce undesirable flavors such as cardboard, stale or sherry-like notes, and a loss of freshness.
2. Stalled fermentation: Oxygen exposure can potentially disrupt the fermentation process and lead to a stalled or incomplete fermentation. Yeast requires an oxygen-free environment to perform its job effectively. Oxygen can inhibit yeast activity and growth, leading to sluggish or stuck fermentation where the yeast is unable to fully convert sugars into alcohol.
3. Spoilage: Oxygen can also contribute to the growth of spoilage microorganisms. While yeast is a desirable microorganism in beer fermentation, other bacteria and wild yeast strains can thrive in the presence of oxygen. These unwanted microorganisms can produce off-flavors and spoil the beer, resulting in an unpleasant taste and potential health risks.
To prevent oxygen exposure during fermentation it is suggested that a brewers take precautions. The use of a sealed fermentation vessels, such as fermenters with airlocks or conical tanks with controlled gas exchange is your budget allows for it . It is also suggested that you purge your keg with carbon dioxide or nitrogen to create a protective atmosphere for your beer. Additionally, careful transfer and handling techniques are employed to minimize the introduction of oxygen during and after the fermentation process.
By avoiding oxygen exposure during fermentation, brewers can maintain the desired flavors, aromas, and quality of the beer. The above photo is the system that I use. After I transfer the wort from the brew kettle and pitch the yeast in the conical fermenter, the only time that the fermenting beer has the opportunity to come into contact with oxygen is when I add dry hops. I try to do this while fermentation is still occurring so that there is a layer of krausen containing CO2 filled bubbles to purge any oxygen that may have entered the fermenter while the lid was briefly off. I use CO2 to transfer the finished beer into a keg that has been purged with the CO2 that was created during fermentation.