Oxygenation and Wort

[adc123]

So I understand the need to get some o2 into your wort: yeast growth. The yeast eat sugar + o2 = more yeast. But if you pitch in the right amount of yeast, like what mr. malty says, how much growth really needs to happen? No aeration of wort means some struggling yeast, too much and there will be too many cells. Isn't it just better to get the right amount in there to begin with?

 

[BeerBalls]

The problem lies in getting the "right" amount and getting the fermentation to start quickly. The longer the struggling yeast takes to reproduce to get that right amount in an under-aerated wort, the higher the likelihood is that you'll develop off-flavors and risk infections from unwelcome bacteria. You want the fermentation to start quickly to develop a cleaner tasing beer. Oxygenating the wort helps the yeast get where they need to be quicker. Also, if you're using liquid yeast such as White Labs or Wyeast, the likelihood is that you are underpitching if you're not making a starter. Not so if you use dry yeast, but that has its drawbacks too. Underpitching makes it take that much longer for the yeast to reach adequate cell count. I do both (oxygenate and use a starter), and I'm pleased with the result. It's also more fun.