What does wort aeration do for my beer? Is it important?
Oxygen needs to be introduced into the wort to promote yeast development during the lag phase, when it is living and reproducing aerobically. This is done by aerating the wort.
Aeration of the wort is generally done by shaking the carboy vigorously. This is the only time that oxygen is to be introduced in the beermaking process
Aeration should be done in a relatively clean (biologically speaking) environment. If the air smells bad aerate the beer somewhere else.
Aerating hot wort has the following advantages:
No risk of contamination from air; better cold break by oxidizing some protein fractions.
Aerating hot wort has the following disadvantages: Polyphenols turned to tannins; oxidation of hop resins; darker color.
Aerating hot wort should not be done for very pale, very dark, or very full-bodied worts, or for delicate styles such as Viennas.