Can we dispel the myth of the 'CO2 Blanket' ?

[Zadkiel]

That's pretty, but is there a purge valve I'm not seeing?

I don't know this model specifically, but yes, the general hop bong design has a gas post and pressure release valve to allow you to use CO2 to purge out the airlock contents.

here's a video of Kegland's one for the Brewzilla line.

 

[sibelman]

There IS a layer (which you could call a "blanket")

but

I wasn't claiming that the CO2 in the fermenter was magically protecting the beer from oxygen

it will take a lot longer than several minutes for the room air to disperse the C02.

but

it only takes seconds of air exposure to the fermenter or keg headspace to get enough O2 diffused/convected into the headspace to cause issues

Boiled down: oxygen-sensitive brews will be adversely affected by opening your fermenter, even briefly.

 

[PCABrewing]

Boiled down: oxygen-sensitive brews will be adversely affected by opening your fermenter, even briefly.

Well why didn't you just say that, sheesh.
I've been hanging on every post to get the final answer...
There is a collection of equations to answer the "how long" question, I found them on the internet.
If you really think it's worth it.

 

[doug293cz]

Well why didn't you just say that, sheesh.
I've been hanging on every post to get the final answer...
There is a collection of equations to answer the "how long" question, I found them on the internet.
If you really think it's worth it.

Go ahead and show us how those equations answer the question. The problem here is that initial conditions, boundary conditions, and the exact details of what air currents result from opening the lid on a bucket are almost totally unknown. And if you did know them in sufficient detail, they would only apply to one specific instance, and not generally across many different situations.

Brew on

 

[worlddivides]

Boiled down: oxygen-sensitive brews will be adversely affected by opening your fermenter, even briefly.

Exactly. But my argument wasn't addressing that. It was addressing Zadkiel's question about why the myth of the CO2 blanket won't go away, even though it's been known to be wrong for decades. And one reason I gave is the fact that, even though CO2 doesn't have a smell, it does burn your nostrils, make you lightheaded, and can make you lose consciousness at high concentrations. And the fact that there's still CO2 in a fermenter weeks after fermentation ended can make people wrongfully think that it's staying there because it's super heavy and will protect their beer. I imagine that most of them would go "Oh, right..." if you explained how oxygen will just mix with the CO2 if you open the fermenter since that's just how gases work, but I doubt many of them get that explanation.

I thought it was an easy way to understand why the myth won't go away, which was what the OP was asking.

It's one of the reason why, since starting kegging, I've only kegged my really hoppy beers and bottled the darker, maltier beers with the exception of a dry-hopped saison (which strangely enough still showed zero signs of oxidation 6 months after bottling, despite bottling from a bottling bucket) and an American Pale Ale (which I bottled directly from the fermenter out of paranoia of introducing oxygen).

The paranoia does get excessive. I'm thinking of just using carbonation tablets or individual dextrose dosing and bottling straight from the fermenter for my next hoppy beer just from imagining how much oxygen could be introduced using the bottling bucket.