Final answer:
Compressed air should not be used in draft systems because the varying composition can affect the beverage quality, and the physical properties of compressed gases pose a risk of the canister rupturing due to pressure changes.
Step-by-step explanation:
Compressed air should never be used as a dispense gas in a draft system due to the nature of gases under pressure and the potential risks involved in handling them. When air is compressed, forces must be applied to overcome the resistance of intermolecular forces. Letting compressed air into a room causes greater dispersal of the gas molecules and requires an input of energy. The nozzle of the canister will feel cold, as the expanding air takes energy away from its surroundings.
Moreover, the use of compressed air could be hazardous as it doubles the pressure inside the canister, leading to the risk of explosion if overfilled or damaged. Containers must have air gaps to allow for expansion and avoid rupture. In the context of drafting systems, oxygen or specific gases are typically used, not only to avoid pressure-related hazards but also to ensure the quality of dispensed beverages remains high. Compressed air, containing a mix of gases including oxygen, nitrogen, and water vapor, can impact the taste and spoilage rate of the beverage.