What should be done after tapping a cask that is to go into service?

When a cask is tapped and prepared for service, the first step is to draw off a small amount of beer, typically measured around 1/3 pint, and discard it. This is referred to as "clearing" the cask and is an important practice for a few reasons.

Firstly, when a cask is initially tapped, it often has sediment and yeast particles that have settled at the bottom during fermentation and conditioning. Drawing off this initial amount helps to clear the beer and ensures that the first servings are bright and appealing to the consumer. Consuming this first pour can lead to an undesirable experience as it may be cloudy or have off-flavors resulting from any residual sediment.

Secondly, this practice allows the beer to settle and reach a proper serving temperature and carbonation level after being disturbed from its cask. This step ensures that the beer is presented in its best condition once it is served to customers.

The other options do not align with best practices in cask service. Drawing off 1/2 pint and serving it immediately may still include unwanted sediment, while letting the cask sit undisturbed for a week would delay service without addressing the sediment issue. Discarding the entire batch before tapping is unnecessary and wasteful, as