Is my starter getting enough O2?

[kiwipen]

When I make starters I put aluminum foil tightly around the opening of the erlenmeyer flask. This is to prevent fruit flies, dust and other unwanted things to get in.

Does this hinder oxygen from getting in? Are there any filters that can be used instead that will allow it to breath, but keep out particles?

 

[stosh]

I use a foam stopper that I soak in star san then I squeeze out the bulk of the star san out of it. I think they come in different sizes.

I've also used tin foil. Both work and I'd say yes you are getting enough oxygen so long as the starters are making beer after pitching.

Do you use a stir-plate?

 

[kiwipen]

Yes, it's on a stir plate.

 

[kh54s10]

As long as you don't put a rubber band or something like that on it I think you are getting enough oxygen. If the pressure difference is enough either direction it will move the foil enough to let oxygen in or co2 out.

 

[SanPancho]

Paper towel and rubber band works well.

 

[Dog House Brew]

I use a coffee filter and a rubber band. Lost 2 starters at the same time to fruit flies, never again

 

[SanPancho]

Your container is too small if flies got to the wort.

 

[Queequeg]

Personally I don't think any sort of passive covering actually provide sufficient gas exchange once the Krausen forms / CO2 production fills the head space.

I am considering putting a conventional air lock but also place a line to an air pump on a timer to ensure the head space is replaced with fresh air.

Alternatively you can build a bioreactor with a diaphragm pump and a sinstred stone on a recirculation.