Aerate wort when pitching to a yeast cake?

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Chad

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I may be overthinking this, but that's kind of what we do, isn't it?

I pitched my Challenger Lager directly onto the yeast cake of the Vienna lager I brewed a couple of weeks ago. I did not bother to splash, shake or otherwise aerate the wort. Yeast uses oxygen during the lag phase to reproduce aerobically, generating enough yeast cells to consume the sugars in the wort. When the yeast has reached critical mass (or the oxygen runs out), it goes anaerobic and begins to consume sugars and produce alcohol and CO2. Somebody please correct me if I've gotten this wrong or missed something in my oversimplification.

I made the assumption that a yeast cake, by default, contains enough active cells to ferment a batch of wort. It just did. So, theoretically, it wouldn't need a lag/adaptive phase and thus wouldn't need added oxygen to reproduce. It should go straight to anaerobic fermentation. Mine sure did. I had steady burbling in the blowoff vessel in three hours.

The question that now bugs me is whether it started fermenting quickly because there was indeed a sufficient amount of yeast and it didn't need a lag time or additional oxygen to take off OR did it simply go anaerobic and start fermenting because there was no other choice, there wasn't enough oxygen to reproduce?

Now I'm wondering if I do this in the future should I go ahead and aerate or give the wort a shot of O2 just to be on the safe side? Or is my theory correct and the huge amount of yeast in the bottom of the fermenter ready to go without an adaptive phase and thus no need for aeration?

Chad
 
I aerate anyways. The yeast will still use the oxygen.

However, you are most likely right, it probably isn't necessary. I have read that a number of brewers, including big breweries, don't aerate their wort at all, they just grow yeast in starters and aerate that. Once they have enough yeast, they just pitch it into the wort.
 
You are probably fine not aerating as the yeast cake has more than enough yeast cells in it. However, some strains produce esters and phenols during the initial reproductive stage that skipping may be missing in your beers. Also, not all of the yeast survive the first ferment, so growing a few more won't hurt anything. I've also read that bombarding the yeast with O2 can actually hurt them, so I've always aerated the wort prior to moving it onto an existing yeast cake. I could be completely wrong about that, but that's the way I do it and it works fine.
 
You'd probably want to aerate if the new wort was high gravity and the cake was produced by a low-grav beer. The cake has a lot of cells for sure, but maybe not enough to completely ferment a high-grav beer. So some cell replication would be necessary, requiring O2.
 
You'd probably want to aerate if the new wort was high gravity and the cake was produced by a low-grav beer. The cake has a lot of cells for sure, but maybe not enough to completely ferment a high-grav beer. So some cell replication would be necessary, requiring O2.

Good point. Luckily this wort was about 1.040 pitched onto a yeast cake from a 1.047 Vienna lager, so it's not going to be working as hard.

Chad
 
i seen a cheap way to aerate the wort last weekend. the guy had a spout on his pot and a hose connected to the spout. the hose had 3 cuts in it one on the top and one on each of the other sides, as the wort passed through the hose it sucked air into it and made the wort very aerated. just thought i would share.
 
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