Which gas is primarily responsible for carbonation in draft beer systems?

Carbon dioxide is the primary gas responsible for carbonation in draft beer systems. When beer is brewed, carbon dioxide is produced during fermentation as yeast consumes sugars and converts them into alcohol and gas. In a draft system, this carbonation is maintained by keeping the beer under pressure, allowing carbon dioxide to remain dissolved in the liquid.

Adding carbon dioxide enhances the mouthfeel and overall sensory profile of the beer, contributing to aspects such as creaminess and perceived freshness. Additionally, the correct level of carbonation is crucial for maintaining the beer's balance and flavor, as well as affecting how the beer appears, such as the formation of a proper foam head.

Nitrogen can be used in some beer styles, particularly stouts, to create a smoother mouthfeel through a different type of carbonation, but it is not the primary gas for carbonation in most standard draft systems. Oxygen, while essential for the initial fermentation process, can lead to off-flavors and spoilage in finished beer, making it undesirable in the context of maintaining carbonation. Hydrogen is not involved in the carbonation process of beer and does not play a role in draft systems. Therefore, carbon dioxide is unequivocally the key gas in achieving the desired carbonation in draft beer.