Carbon dioxide (CO2) is indeed a byproduct of the brewing process. When you ferment beer, which is the process of converting sugars into alcohol, CO2 is produced along with the alcohol. This is because yeast, the microorganism responsible for fermentation, consumes the sugars in the wort (the liquid extracted from malted grains) and produces alcohol and CO2 as metabolic byproducts.
During fermentation, yeast breaks down the sugars in the wort through a series of chemical reactions. One of these reactions is anaerobic respiration, where yeast converts sugar molecules into alcohol, CO2, and energy. The CO2 is released as a gas, creating bubbles that rise to the surface and eventually escape from the fermenting vessel.
CO2 serves a crucial role in the brewing process beyond being a byproduct of fermentation. After the beer has finished fermenting, it is commonly carbonated to give it a pleasant effervescence. This is achieved by introducing additional CO2 into the beer. There are various methods for carbonating beer, such as natural carbonation through bottle conditioning or force carbonation using pressurized CO2 tanks.
In my personal experience as a brewer, I have witnessed the production of CO2 during fermentation firsthand. It is always fascinating to see the vigorous activity in the fermenter as the yeast converts sugars into alcohol and releases CO2. The bubbling of the airlock or the foaming in the fermentation vessel are clear indications of the CO2 being generated.
To summarize, CO2 is indeed a byproduct of brewing beer. During fermentation, yeast metabolizes sugars and produces alcohol and CO2. This CO2 is essential not only for the fermentation process but also for carbonating the beer later on.