starter and oxigenation

[philbrasil]

I am wondering if oxigenating a yeast starter continuously won´t be bad for the yeast. Any thoughts?

I heard from "How to Brew" that you make a small amount of wort and pitch your yeast and let it ferment out, then you can make another wort and grow up your cell count again, but he never mentioned when you should not aerate. Can you do it all the time guilt-free?

[oneal66]

Constant aeration is good for your starter. There are a few problems though. You may have a problem spewing krausen out of your starter vessel if you keep pumping fresh air into the starter. You may run into the same problem with aeration on a stir plate. It will probably just bubble out of the vessel. Another problem could come from contamination. If you're just a little off on your sanitation you might end up steadily pumping bugs into the starter.

You also said oxygenation in your post. If you constantly add 02 you will end up damaging your yeast. Filtered air is ok, pure 02 can be toxic if you add too much. So unless you're using filtered air, I would just add 02 in a short burst (less than a minute)

[philbrasil]

Sorry, I really did mean aeration. I guess my source of aeration would be shaking (or swirling) the erlenmeyer flask with an airlock in it.

And I am thinking about buying a stir plate for that. So I guess I am ok doing one of these 2 things right?


After that, how will I know when to pour the fermented wort out and make some more and put it back in to get more yeast? (I am making yeast cultures in small "vials" or test tubes, so I will start with a small volume of yeast)

[siwelwerd]

You don't want an airlock on your starter. The point of stirring/shaking is to introduce fresh oxygen into the solution--if you have an airlock on there, the CO2 production will purge the environment of other gasses (specifically oxygen). I use a piece of sanitized aluminum foil loosely over the opening. This allows fresh air to come in, and CO2 to get out.