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General Category => Yeast and Fermentation => Topic started by: richardt on July 16, 2010, 08:46:33 PM

Title: Is it possible to "over aerate" a yeast starter
Post by: richardt on July 16, 2010, 08:46:33 PM
I've been kinda busy.  I've had a yeast starter (Wyeast 1056) going for over a week now (1L size, 1.040 OG).  Nice and creamy yellow color, still got a small dimple in the top of the fluid. 

Assumming the yeast are done eating all the sugars and have attained maximum growth and reproduction, am I harming the yeast by keeping it on the stir plate and aerating it?  (Air only, no Oxygen).
Title: Re: Is it possible to "over aerate" a yeast starter
Post by: bluesman on July 16, 2010, 08:56:22 PM
Once the yeast has finished fermenting it's no longer necessary to stir. Cold crash and decant before pitching.
Title: Re: Is it possible to "over aerate" a yeast starter
Post by: tom on July 16, 2010, 09:01:39 PM
Not with air. But definitely decant before pitching.
Title: Re: Is it possible to "over aerate" a yeast starter
Post by: narvin on July 16, 2010, 10:38:53 PM
If you're not pitching at high krausen, you'll want to refrigerate it once it ferments out.  It's not so much the air, but the warm temperature and waste products that could lead to decreased viability over time.
Title: Re: Is it possible to "over aerate" a yeast starter
Post by: richardt on July 17, 2010, 03:17:45 AM
Thanks gents,

I'll take it off the stir plate and put it in the 40F fridge tonight to cold crash it.

It'll be good for a few days, right?

I still have those yeast cakes from my IPA (can't wait to check and see if they've been good or bad (acetobacter).)
Title: Re: Is it possible to "over aerate" a yeast starter
Post by: majorvices on July 17, 2010, 01:13:32 PM
As an aside and somewhat along the same lines I have killed a yeast starter with pure o2 before. But it would be impossible to do this with pumped air or on a stir plate.
Title: Re: Is it possible to "over aerate" a yeast starter
Post by: astrivian on July 22, 2010, 02:30:50 AM
What is "cold crash"?
Title: Re: Is it possible to "over aerate" a yeast starter
Post by: a10t2 on July 22, 2010, 02:37:43 AM
What is "cold crash"?

Putting the starter (or main batch, for that matter) in the refrigerator. It forces the yeast to go dormant and flocculate more quickly.