Which type of draft system is typically not exposed to ambient air?

The glycol-cooled draft system is designed to maintain beer at optimal serving temperatures and is typically not exposed to ambient air. This type of system uses a refrigerated glycol solution that circulates through insulated lines, offsetting the potential temperature fluctuations that could arise from ambient conditions. The insulated, enclosed nature of the glycol-cooled system helps to ensure that the beer remains cold as it travels from the keg to the faucet, minimizing heat transfer from the environment.

In contrast, direct draw systems can be exposed to ambient air, especially if the kegs are placed in a walk-in cooler or at room temperature; air-cooled systems rely on ambient air to cool the beer but can still be subject to temperature variations; and gravity-served systems, while they don't require mechanical cooling, are typically open to the environment and can also be affected by ambient temperature, causing inconsistencies in serving conditions.

By understanding that glycol cooling minimizes environmental exposure, it becomes clear why this is the correct choice for a draft system type that maintains a controlled serving environment.