Over-Aerating?

I heard somewhere that it is possible to aerate TOO much. Is this true. I use and aquarium air pump that is rated for 40 gallons on my 5 gallon batches. How long should I run the pump? I have been aerating for about 5 minutes or so.

What yeast are you using and how have you prepared it?

the 40gallon rating has nothing to do with the 5 gallon you are brewing. Apples and oranges.

I have read that by the aeration method the max you will achieve is 8ppm in solution as a direct result of the composition of air itself. I have never heard one can "over aerate".

However, I do read all the time that one can over oxygenate that is, use too much pure Oxygen. i don;t think I have ever seen the DO limit for O2 toxicity on yeast.

I read you could over oxygenate with straight O2, but with an aquarium pump for 5min you are fine.

While on the subject of O2. How long do you oxygenate if you have the gear?

1-2 minutes, but others do more/less.

I once aerated with the O2 tank and 5 micron stone for 12 minutes and the beer turned out just fine. I would never do it again but what the hell did I know I was a NOOB!!!

Because I make partial boil recipes, I run my aquarium pump and aerator stone in the cold water that I add back to my wort to cool and achieve my 5 gallon volume. I run the aerator the entire time I'm steeping and boiling. Cold water will saturate more than warmer wort. I add my cold water, check temperature, pitch, install airlock, and start cleanup. No aerator in the wort.

You can't over-aerate with air, but you will get to a point of diminishing returns. With oxygen you could theoretically over oxygenate, but on a homebrewing scale it isn't very likely. Pressure has a lot to do with how much O2 a liquid can hold, and in a 5 gallon batch, or even a 20 gal batch there isn't enough weight on the liquid to allow it to hold enough O2 to become toxic to the yeast. Just run your O2 stone for 1-2 min and you will be fine, any more and it will just be wasteful because all the extra O2 will just bubble out of the wort.

Now if you are brewing on a 30bbl system that is a lot of weight/pressure on the wort and it is capable of holding a lot more O2...