[majorvices]

You could put some foil over the fermenter opening. If that's good enough for starters it should be good enough for beer that is done fermenting.

No, it's not. Starters are not making beer, they are growing yeast. Foil won't keep out o2 and you will ruin the beer with oxidation if you don't seal the beer under a blanket of co2.

[denny]

You could put some foil over the fermenter opening. If that's good enough for starters it should be good enough for beer that is done fermenting.

No, it's not. Starters are not making beer, they are growing yeast. Foil won't keep out o2 and you will ruin the beer with oxidation if you don't seal the beer under a blanket of co2.

If I'm using a carboy, I put fpoil over the opening and secure it with a rubber band.  How will that let in more O2 than an airlock?

[morticaixavier]

You could put some foil over the fermenter opening. If that's good enough for starters it should be good enough for beer that is done fermenting.

No, it's not. Starters are not making beer, they are growing yeast. Foil won't keep out o2 and you will ruin the beer with oxidation if you don't seal the beer under a blanket of co2.

If I'm using a carboy, I put fpoil over the opening and secure it with a rubber band.  How will that let in more O2 than an airlock?

sealing with a rubber band is different than putting foil over a starter where it is lose specifically to allow o2 interchange.

[majorvices]

You could put some foil over the fermenter opening. If that's good enough for starters it should be good enough for beer that is done fermenting.

No, it's not. Starters are not making beer, they are growing yeast. Foil won't keep out o2 and you will ruin the beer with oxidation if you don't seal the beer under a blanket of co2.

If I'm using a carboy, I put fpoil over the opening and secure it with a rubber band.  How will that let in more O2 than an airlock?

Put a rubber band over foil and over the end of a piece of PVC and see if you can breath in.

[denny]

Put a rubber band over foil and over the end of a piece of PVC and see if you can breath in.

That's not exactly an equivalent, Keith.  The beer isn't generating significant back pressure.  Not to mention that I've done it many times and it works! 

[Pinski]

You could put some foil over the fermenter opening. If that's good enough for starters it should be good enough for beer that is done fermenting.

No, it's not. Starters are not making beer, they are growing yeast. Foil won't keep out o2 and you will ruin the beer with oxidation if you don't seal the beer under a blanket of co2.

If I'm using a carboy, I put fpoil over the opening and secure it with a rubber band.  How will that let in more O2 than an airlock?

Put a rubber band over foil and over the end of a piece of PVC and see if you can breath in.

If you're crash cooling in a carboy you're going to get the same pressure loss and therefore O2 intake regardless of whether you use an airlock or foil with a rubber band. Foil and band may provide more resistance but it's going to stabilize with the same volume eventually.  Personally, I prefer the physical barrier of an airlock. Majors point of a CO2 blanket makes sense, if the o2 mixing occurs gently enough, perhaps the CO2 blanket could protect the beer from oxidation or at least minimize it.

[majorvices]

It generates enough back pressure to suck water back through the airlock, though. I dunno, not a practice I'd feel comfortable with. Plus I've lost too many batches to fruit flies in buckets and carboys I thought were sealed sufficiently.

[Pinski]

It generates enough back pressure to suck water back through the airlock, though. I dunno, not a practice I'd feel comfortable with. Plus I've lost too many batches to fruit flies in buckets and carboys I thought were sealed sufficiently.

Exactly.

[bluesman]

I would advise you to use an "S" bubble airlock or make sure you don't overfill the two-piece style with sanitizer when you crash cool from fermenting temps down to near freezing.  The beer condenses as it cools rapidly and will draw air in through your airlock. I had a two piece airlock allow the sanitizer to be drawn into a batch once.  Haven't had that issue with the "S" shaped one-piece airlocks when crash cooling. You could pull the airlock and use a bung too, but it's still going to balance the pressure at some point.

+1

I also use an S bubble airlock, as it won't allow the liquid in the airlock to be sucked back into the beer. Plus it keeps undesireable pests and such out of the beer.

[klickitat jim]

How about a flexible rubber carboy cover that allows for expansion and shrinkage without the introduction of foreign materials or too much O2? IE balloon

[Pinski]

How about a flexible rubber carboy cover that allows for expansion and shrinkage without the introduction of foreign materials or too much O2? IE balloon

Seems like i read somewhere about somebody that fixed a baloon to the airlock/blowoff tube near the end of fermentation to allow a reasonable fill of the balloon without destroying it.  Then when it was time to crash and the gas laws went to work, only the CO2 from fermentation was drawn back into the carboy with no O2 or sanitizer.  Very clever solution, but not practical in my brewery. 

[hopfenundmalz]

How about a flexible rubber carboy cover that allows for expansion and shrinkage without the introduction of foreign materials or too much O2? IE balloon

I would worry about O2 division with a balloon. They go flat over 6 weeks right?

[klickitat jim]

I have no clue on that. I remember my pappy putting balloons on his wine/mead carboys once airlock activity stopped. I remember the balloon would slowly inflate over a week or so then slowly deflate. When it started deflating he took his final gravity readings. They were stubby balloons with an opening big enough to snap over a carboy.

This was back in the 70s. I'm sure methods have changed.

[tommymorris]

You could put some foil over the fermenter opening. If that's good enough for starters it should be good enough for beer that is done fermenting.

No, it's not. Starters are not making beer, they are growing yeast. Foil won't keep out o2 and you will ruin the beer with oxidation if you don't seal the beer under a blanket of co2.

OK. I didn't think about O2. I was just thinking of microbes.

[1vertical]

Ahem....throat is now clear.  We have fermented our beer to primary conclusion.
It does contain en-trained gas which is CO2.  I am of the school where we now
secondary (i.e. lager) in a CO2 filled  Corny Keg.  We rack from primary vessel into a keg where some of
the en-trained gas is released. This Gas is heavier than the oxygen in the canister
and displaces oxygen upward toward the keg pop off vent. After racking from primary
to keg, I apply gas under pressure from my CO2 cylinder to the vessel forcing
the lighter oxygen even harder against the pop off valve.   I then pop off the
valve releasing the lighter oxygen from the beer keg. MINIMAL exposure of the beer
to oxygen.  At this point the keg is purged and ready to lager....reduce temps and
enjoy good beer.

(Sound technique governed by physics? IMHO)