Foam stopper, foil, airlock, or .?

[GorillaMedic]

Getting setup to do my first yeast starter for our next batch. After reading a bunch of things, I feel like I've gotten a handle on how to use a yeast calculator and how to prepare my starter.

I am left wondering what I should use to cover the top of my flask. A lot of sources talk about using sanitized foil, a few talked about using a foam stopper, and I also saw an airlock on one. What's the rationale behind these recommendations—and really, what should I use?

 

[nyks]

I don't really know enough to get into the pros and cons, but personally I just use some sanitized foil. It seems to be working out okay.

 

[TexasDroughtBrewery]

I second foil...it worked just fine for me.

 

[david_magnuson]

From what I have read, the yeast needs fresh oxygen to grow the colony, so the airlock is not recommended. The foam and the foil are not airtight and allow new oxygen into the system. They are there to keep buggies from free falling in. I've been using foil with no problems....cheap and recyclable.

 

[kh54s10]

The foam works but I had krausen rise up and saturate the foam. It did not seal but was a mess. I have since just used foil.

You DO NOT want to use an airlock as you do want oxygen to help the yeast reproduce as healthy as possible. They need the oxygen and the airlock will block the introduction of oxygen.

 

[SeraW]

I trust foam for more thorough exchange than I do foil. I'm 99% sure that it's not different but it does me no harm and I'd rather wash and sanitize a foam stopper repeatedly than throw out more foil.

 

[eadavis80]

I use my foam stopper if I only have 1 starter going. One time I had two at the same time and the other one I used an airlock. I did not notice any difference, but I guess I 'should have' used sanitized foil, but again - I noticed no difference.

 

[laredo7mm]

I use my foam stopper if I only have 1 starter going. One time I had two at the same time and the other one I used an airlock. I did not notice any difference, but I guess I 'should have' used sanitized foil, but again - I noticed no difference.

I have never used an airlock on my starters, but I find it hard to believe that any oxygen gets into the flask when foil (or similar loosely fitting cap) is used. I think the most important part is the stirring which gets rid of excess CO2 from the solution.

My theory is that if I am doing a 1 liter start in a 2 liter flask, that head space is going to fill with CO2 and be at a positive pressure so CO2 will constantly be escaping from under the foil. Since CO2 is heavier than O2, and is constantly escaping from under the foil, how can O2 get in?

 

[mongoose33]

I really doubt there's much oxygen going in past the foil. The fermentation creates CO2, which creates a positive pressure. I don't see how oxygen is going to get in past that.

 

[laredo7mm]

...I am left wondering what I should use to cover the top of my flask...

I freeze my yeast in 4 ounce canning jelly jars. The type with the flat lid that has the rubber seal with the ring that goes around it. So after thawing out the yeast and putting them in the starter, I rinse the flat top, sanitize it, and place it on top of the flask. No foil, no stopper, no airlock.

 

[IslandLizard]

I really doubt there's much oxygen going in past the foil. The fermentation creates CO2, which creates a positive pressure. I don't see how oxygen is going to get in past that.

That gas exchange mechanism across a (loose) aluminum foil hood has always been puzzling to me too. I don't think a foam stopper behaves much differently or has much advantage either. Sure there is some gas exchange, but there's certainly a barrier there.

As to CO2 out, that would only happen during fermentation, not during the growth/propagation phase. Basically once the propagation phase is over, the cell count is maximized. Now the changeover is gradually, so there's a time both processes, propagation and fermentation, coexist.

From what I gather oxygen assimilation by the yeast is rather quickly, so after an hour, or 2 at the most, all oxygen that could be used has been used.

 

[SeraW]

From what I gather oxygen assimilation by the yeast is rather quickly, so after an hour, or 2 at the most, all oxygen that could be used has been used.

That is kinda why I'm drawn towards the vitality starter method lately. Works so well for me...