Oxygen can lead to off flavors in beer after fermentation, but dissolved oxygen in wort is an essential element for yeast health. Specifically, yeast cells rely on oxygen for the biosynthesis of cell membranes, a critical step in the growth and reproduction of pitched cultures.
There are many effective methods for getting oxygen into wort, but nothing beats pure oxygen for speed and efficiency. Experiments at Wyeast Laboratories have shown that just 60 seconds of pure oxygen, pumped into chilled wort through a diffusion stone, can achieve 12 parts per million (ppm) of dissolved oxygen. Wyeast notes that most yeast strains require 10 ppm or more of dissolved oxygen for optimal health, perhaps a bit more for lagers and high-gravity styles.
Using pure oxygen is actually quite simple. You really just need four things: