What should you examine on the keystone before tapping a cask?

In the context of tapping a cask, examining for gunk on the keystone is essential for ensuring the quality and integrity of the beer. The keystone, which is a small wooden plug at the end of a cask, can often collect sediment, yeast, and other impurities over time. This buildup can affect the beer's flavor and clarity when it is poured. By checking for any gunk or buildup, the individual tapping the cask can make informed decisions about whether the cask is ready for service or if it needs additional cleaning or maintenance.

While other aspects such as pressure readings, beer clarity, and cask age are important when considering overall beer quality and performance, they do not specifically pertain to the immediate inspection of the keystone prior to tapping. Ensuring that the keystone is clean and free of contaminants is a critical first step that can influence the beer's presentation and taste as it is served.