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.
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.
+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.
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.
I would worry about O2 division with a balloon. They go flat over 6 weeks right?
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.
OK. I didn’t think about O2. I was just thinking of microbes.
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)
I swap out the airlock for one of these - let’s out CO2 pressure, does not let O2 in.
http://morebeer.com/products/silicone-stopper-breathable-carboy.html
I was nervous about those in fruit fly season tom…??
Why? The edges all seal very well and don’t draw anything into the carboy. If a fruit fly can get through one of those then they can get past a solid stopper.
I need to get one of these do-dads. Thanks for the find Tom.
I have a couple of these (purchased on Toms recommendation, thank you Tom) that I use on my sour carboys. I don’t worry about flies or othe nasties getting in but I guess I’m skeptical that the design really prevents O2 from getting if and especially after CO2 has been purged and therefore necessarily loosened the seal between the silicone ports and the cap. The cap is only held in place by a semi-snug silicone on silicone contact. It’s design is such that going out is certainly a path of lesser resistance. I just wonder if reduced pressure inside the vessel due to cooling will really reset the cap sufficiently to prevent o2 from getting in.
I have one of those,tom. I was hesitant to use it with all the work I had in the solara
just did not want to take the chance. I sealed the thing with the same type white
silicone rubber solid bung…after “s” tube bubbler quit.
And I was having a fly attack from some fruit from the store…little buggers
Having been to some CA wineries recently, there were many barrels with those, and a lot of fruit flies. Didn’t taste vinegar at any of them.
I’ve used the waterless silicon airlock doodads and I like them. When I remove one after cold crashing air gets sucked in and it’s obvious that it has indeed held a vacuum. I dip it in star san before installing in a glass carboy but the star san makes it slippery so that, after pushing it in it pops back out and gravity is the only thing keeping it in the opening. But it still seems to seal well enough until the pressure drops with cooling and the stopper is sucked in tight.
It seems with mine that the top lays flat and takes quite a bit of pressure build up before it “burps” to relieve it. I am not saying they are impermeable to O2, but they seem safer to me than a cork since they can burp.