Oxygenation required?

If I am pouring a new batch of wort over an existing yeast cake from a previous batch, do I need to aerate / oxygenate?

I thought that oxygen was needed only to help with yeast reproduction, and not the actual fermentation process... so since I am putting new wort onto what is probably an over-pitching quantity of yeast, why would I need to oxygenate?

Thanks for any replies, I'll be pouring the wort in about 2 hours...

DJG

No, you really wouldn't. However, you will better off sticking closer to a proper pitching rate than to grossly overpitch. I've done the yeast cake thing and wasn't really happy with the results. Why not harvest the cake and just repitch what you need? Mr. Malty has a tab for repitching from slurry.

BBL_Brewer said:

Why not harvest the cake and just repitch what you need? Mr. Malty has a tab for repitching from slurry.

Click to expand...

Amen! Been doing that pretty much since I went all-grain & have had great anecdotal success. Haven't gotten my BJCP score sheets back, but my fermentations have been increasingly on point using the rep itched amounts according to mrmalty.

Yes, you should still aerate. If you don't aerate, you will not get any new yeast, and the old yeast may not be up to completing fermentation.

..... That is one of the problems with 'Over-pitching' is that you don't get many new yeast cells and the beer can stall before finishing. You will also get less flavor esters, and possibly more fusel alcohols.

As noted by others, just take a part of the cake and ferment normally. My rule-of-thumb, is to use about 1/4 th of the cake for a similar gravity beer.