The boiling process will remove oxygen and oxygen is a vital element for good yeast fermentation.
So for those brewers who are boiling their wort it is a good idea to aerate the wort prior to pitching the yeast. This should always be done in 'cooled' wort to prevent oxidising the melanoidins in your beer leading to stale flavour.
Aerating your wort BEFORE pitching the yeast is good brewing practice and should NOT be confused with aerating the wort during fermentation, or after fermentation which can lead to oxidisation casing a strong stale flavour in the finished beer.
There are several basic methods for aerating the wort before pitching the yeast.
SPLASHING…This can add some oxygen to the solution and is usually sufficient in most instances.
AGITATION….This can be done by vigorous stirring or whisking the wort with an agitation rod., usually attached to a drill. This method will add more oxygen into the solution than splashing
INJECTION The simplest setup involves using an inexpensive air pump with an aeration stone, A more elaborate setup would include an oxygen bottle, and regulator to inject oxygen