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Yeast starter flask - no airlock?

I am curious why it seems to be ok to not have an airlock of some type on your yeast starter. I did make one a while back and used the foam “plug” , had no issues but am just curious why there is not as much concern on a starter verses during the full batch fermentation.



With a flask I have always just put aluminum foil over the top. I’ll take a stab at why no air lock. Since the starter is normally used when the yeast is most active the outward CO2 pressure keeps anything bad out so it only needs a cover so nothing falls in. If you don’t use the starter right away, they say to just stick it in the fridge. A refrigerator isn’t the most germ free environment so that doesn’t sound smart but I guess the pressure keeps up until it has completely fermented out.

No reason not to use an air lock that I can see so if it makes you feel better, why not? For my normal batch size of 20 gallons I need to step up starters to gallons so I use a 5 gallon glass carboy and stick an air lock on like normal. Never really though about anything else.


Thanks. I had a bunch of airlocks sitting around so I used one on this starter. Makes me a little less worried about it.

I just use star sanned saran wrap with a rubber band to hold it on.on my starter jugs.

Loose sanitized tin foil for me.

I understand that as it is getting started, you are to allow the air to move into your flask, albeit somewhat filtered… The yeast are so numerous that the risk of an outside organism taking over near impossible… Once the yeast are started the CO2 is the protector of the yeastie clan!! As I understand… Sneezles61

Aluminum foil and plastic wrap should be sanitary off the roll. Again, if it makes you feel better, sanitize it.


Thank you Mr. Sunfish!! Are you a pro brewer? Or, just really entrenched into ALL the details of brewing… You are very knowledgable! Sneezles61

Great explanation.

I hope I didn’t " choke " my French saison starter. I did not notice a ton of activity but the flask looks like beer with the yeast cake on the bottom. Now in the fridge and will use it tomorrow when my son comes to brew. I remember my last starter was pretty active but it may have been for a wheat beer. I have never used this type of yeast( wyeast liquid 3711 French saison).

I will keep my fingers crossed and maybe pitch the entire flask in case I still have some in suspension.

No…not a pro brewer…just a “geek” that likes to drink/make beer.:wink:

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I enjoy what you bring to the party… Maybe need a bit more of your why and how come? Possibly? Sneezles61

Based on the above comment I will change my starter equipment. Thanks!

It will be fine. Starters often don’t look like anything is or was going on. Any attempt will be better than none.

Yes you are right. I pitched it at 3 pm yesterday and looked at 6 am this morning and it has high krausen and the airlock is bubbling away…
I guess different yeast strains act differently in the starter. My Bavarian wheat was super active.

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