Aeration show O2 after growing yeast on stir plate

[Zen_Brew]

I have a question on the aeration show. I'm not entirely sure I understood something John said about the need to aerate after growing a starter on a stir plate. If I understtod correctly John said if you have grown the yeast up on a stir plate there was no need to aerate when you pitched that yeast.

I make starters for just about every batch based on the Mr Malty calculator. I definitely noticed better attenuation when I started injecting O2 into the wort for 1 minute just before pitching beer. It seems obvious to me based on the cake in the fermentor that the yeast goes through another substantial growth phase in the fermentor even if you did pre-grow it on a stir plate. I also constantly hear Jamil aerates his wort even though I'm sure he makes a stir plate starter with most/all of his batches.

I'm sure I missed something or misunderstood. Help a brew brother get his head on straight. Thanx

[BadRock]

Depending on how long the yeast is on the stir plate you may or may not need to aerate the wort. What he said was that if you only run the yeast on the stir plate for about 4 hours and then pitch there really isn't a need for additional O2. But if you allow it to go through the whole cycle and leave it on for around 24 hours you will need to aerate.

I would also add that if you only run it for 4 hours you are not getting the growth that you probably are looking to accomplish, I think that statement was more of an example of the yeast using the need O2 before entering the next stage.

[Zen_Brew]

Thanx for the answer BadRock. I usually run the stirplate for about 20-24 hours then cut the stirrer. I try to time my brewing so I am pitching somewhere in the +20 to +30 hour area after begginning the starter so I am catching the yeast usually near or just after peak krausen, while they are still active.

For the time being I plan to continue the aeration of my wort just before I pitch as I have definitely seen my FG consistently end up a couple points lower than it had been before I used oxygen to aerate. I will keep my ears out to any more information on the subject however.

[BigNastyBrew]

Well, without O2 in the wort, you wouldn't get any additional growth (obviously). Would't that cause too clean of a fermentation, in most circumstances? Ester production is generated during the exponential growth phase, right? Or am I wrong on that?

[andy77]

Along the lines of what Badrock was saying, my impression is that they were speaking theoretically, as a way to dissect the concept of yeast metabolism.

I think that, in practice, you would have to be such a uber yeast-whisperer to know exactly when a specific strain of yeast has built up it's glycogen reserves that it would be next to impossible. Also unnecessarily difficult compared to just throwing an O2 stone in the wort for a minute or two is much easier.

[jamilz]

Keep in mind that every time a cell divides, half of every thing goes with the other cell. Even after dividing, the cells can take up the O2 and use it for cell membrane health for the next budding. You can't really juice up the cells so much in the starter that they would never use the additional O2.

[Zen_Brew]

I think that, in practice, you would have to be such a uber yeast-whisperer to know exactly when a specific strain of yeast has built up it's glycogen reserves that it would be next to impossible.

I like that quote andy...... "The yeast Whisperer" Brilliant!!