What is a likely cause of excessively foamy beer from the tap if the pressure is too high?

When the pressure is too high in a draft beer system, it can lead to excessive foaming due to the carbon dioxide (CO2) being driven out of solution. In draft beer, proper carbonation is maintained when the CO2 is dissolved in the liquid at the correct balance of pressure and temperature. However, if the pressure applied to the keg is too high, it increases the rate at which CO2 escapes from the beer as it is poured. This results in excessive foam because the beer is unable to maintain its carbonation in the glass, leading to a large amount of bubbles.

In this context, beer temperature is also a significant factor; if beer is too cold, it can hold CO2 better, while if it is too warm, CO2 is more likely to escape. However, when the main issue is identified as excessively high pressure, the direct cause of CO2 being out of solution leading to foam is the primary focus. Thus, identifying CO2 out of solution as a cause for this issue accurately captures the complex interaction of pressure and carbonation in draft systems.