I have read not to use an air lock when making a starter as they do not allow the exchange of co2 for O2.
What about these? http://whatman.com/BugStopper.aspx
I can get these as a sample so it would not cost me anything.
They seems like a good idea. I am currently using foil.
My setup is a 2 liter Erlenmeyer flask with stir plate.
Nothing wrong with foil. It's what I and many others use.
How do you BBQ an elephant....first you get your elephant....
I am not saying that there is anything wrong with foil, it has worked well for me also. I am curious if anyone knows if these will allow the needed exchange of gasses along with being a better barrier than foil.