Stir plates, O2 and the lifetimes of a fungus.

[rich]

This new topic is an off shoot from here
http://www.thebrewingnetwork.com/phpBB2/viewtopic.php?t=1849&start=15
It is intended to continue the stirplate starter discussion.

The stirplate does draw in air. It does have other effects, but this is the one you really want. This is the right amount of O2 for a starter, not continuous pure O2, not a shot of O2 at the start.
There have been studies on the effect of stirring on yeast health. It is not a problem. Don't worry about it. For those interested, check the papers on the ASBC site.

-Ok, your saying a shot of O2 is not helpfull in a starter. Does this depend on if you pitch at high krausen, or if you ferment your starters out to harvest a slurry?

-I don't know what the "papers on the ASBC" site are. Post a link, please.

-Can you spare a bit of change for a poor old alter boy, Father Pope?

[DannyW]

I'm getting full of questions on stir plates too. I would also like to see that link so I can do some reading.

My starters seem to get pretty warm on the stir plate, so I was going to put the whole contraption in the fermentation freezer at 68F. If I'm counting on the whirling to draw in oxygen, then am I wasting my time because the freezer is full of CO2?

I'm also seeing conflicting information on how fast to run the stirrer. Some say make a vortex, others say just enough to keep the yeast in suspension. What is the correct answer? If nobody knows, this is starting to sound like a great experiment!

[jamilz]

No, I'm not saying that a shot of O2 is not helpful. I'm making a statement as to the best method of providing O2 to a starter.

http://www.asbcnet.org/

[rich]

Sorry Jamil, I wasn't slamming ya, just trying drum up some debate on stirplates.

What I should have asked was: "Is a continuous infusion of air with it's 27% contribution of O2 better for a starter? Does a pure O2 infusion at the "git go" disapate too quickly to complete the aerobic stage?

Thanks for the link. I'll check it out when I should be working. Oh, and you didn't answer my request for spare change. I just need a cup of coffee....

[Kaiser]

I'm starting to like this forum. People actually start new threads when things start to get off-topic. I have been trying this on other forums and there the discussion semed to stop suddenly when a new thread was started

What I should have asked was: "Is a continuous infusion of air with it's 27% contribution of O2 better for a starter? Does a pure O2 infusion at the "git go" disapate too quickly to complete the aerobic stage?

I'd say that a continuous infusion of air is better (and cheaper) than pure O2. In large concentrations O2 is toxic to the organism. That is also true for humans. I feel that the best starter is one where the yeast never has to leave its aerobic state and can use the sugars much more efficiently for reproduction. But continuous aeration may cause a foaming problem with your starter.

One system thay might be even better for yeast propagation would be a conical vessel with an aeration stone at the very bottom. The rising air would aerate the wort and create enough motion to keep the yeast in suspension. But who is going to build a mini conical for doing this at home.

But then I also read this BYO article that makes me rethink this idea: http://byo.com/mrwizard/1128.html

Jamil, thanks for the link. I'm always looking for good brewing releated reading on the web

Kai

[ubriaco]

I dont have the cash for a stirplate and like my PI too much to jack one from the lab, but I do have continuous aeration through an aquarium pump running into a 6L and 4L ehrlenmeyer flask. I also feed the yeast shots of sugar every other day 20g/L with 3g/L nitrogen. It does foam like crazy but I use cooking oil to keep that down. Just for info, if you use this with a stirplate you dont need the oil, and will get more growth.

If you make starters once the yeast starts fermenting in that starter, there is no longer any division going on, so by continuous aeration you can keep them in log growth phase, which makes the population double every 90min.

Just to tell you how efficient this is, I started with a bottle of Rogue (1 22oz bottle) on monday, I hit it with sugar on wed. thur. and fri., by sat. I had enough yeast to effectively ferment 10gal of IPA. My lag time was 12hr.

oh yeah, dont waste money on injecting O2 with your starter, save that for your wort. and Kaiser, you are correct O2 is toxic at high concentrations.

[Kaiser]

It does foam like crazy but I use cooking oil to keep that down.

How do you make sure that no oil gets in the wort?

Kai

[ubriaco]

it is a very small amount so it really doesnt matter, also if it were to make it into your finished product, it would sit on top of your fermenter, so when you rack to keg or bright tank it would be left in that little bit that doesnt get sucked up by the siphon