Aerating When Moving from Mash tun to Boil Pot

I suggest listening to this particular episode of Brew Strong about Hot Side Aeration.

It features Dr. Charles Bamforth, one of the foremost brewing scientists who is willing to talk to us homebrewers.

He essentially dispels the majority of myths about HSA saying that it is far more important to avoid Cold Side Aeration. (Edit: Dr. Bamforth does not dispel the myth of HSA, and I don't know why the myth that he did dispel it ever arose. What he said, if you can hear him above Mr. Malty's buffoonery, is that HSA is real, but commercial brewers have more significant factors that should be dealt with first, like storage temperatures for finished beer. This is major issue for commercial breweries trucking their beer across country, but almost non-existent for homebrewers, especially those who keg. This would mean that HSA is an even more critical factor for many/most homebrewers.)

In short, you probably don't need to worry about Hot Side Aeration much at all, at least not until after the boil is complete.

http://www.thebrewingnetwork.com/shows/475

the biggest danger with hot side aeration for homebrewers is that, since the air entrained will foam out before it boils, it increases the risk of a boil over on your wife's stove. this is an issue you probably know how to deal with by the time you go all-grain so... yeah...

I agree with what mdma said about HSA, but I'd also like to address the foaming aspect. Foam in beer is formed by a matrix of proteins and carbohydrates. It's been said that these proteins only have the ability to form foam once. If you create too much foam in your wort, you could affect the head on your finished beer.

You'll call forth the legendary dormant beast of HSA! That's hot-side aeration - introducing oxygen into the wort which could cause some compounds to oxidize.

At least, that's the myth. HSA is a bit like santa claus, and autolysis, which although real, rarely affects homebrewers.

If you splashed the entire wort like this then there's a good chance the beer would oxidize quicker. But if it's just from the first runnings into the BK, then you don't need to worry. Using a hose to quietly transfer wort between the different vessels is considered good practice.

Just some conjecture now - I don't have any hard facts to back this up, but perhaps the reason that HSA is not common for homebrewers is that we boil the wort quickly after collecting it - usually within an hour, often much less. Once the wort is boiling, any dissolved oxygen is driven off. With commercial breweries, I believe it takes much longer for the brew to reach a boil, and so there is more time for the dissolved oxygen to bind and oxidize. Just a guess.