How does one go about this without introducing oxygen or creating a vacuum? It might be an impossible question, but hopefully someone out there has a good method.
Thanks for any help!
As the owner of a few of these the answer is one doesn’t. 
How do you personally cold crash (if you do)?
I do not.
This is what I did: https://www.homebrewersassociation.org/forum/index.php?topic=20241.msg258272#msg258272
You could supplement what I do by pumping in more CO2 as the temperature drops to keep it under positive pressure.
My experience has been that after the initial fill with CO2, it will hold a vacuum as the wort contracts which can then be broken on the day you transfer by adding more CO2. Don’t forget to break the vacuum before you open the ball valve or a bunch of air will get sucked in.
I, too, have stopped cold crashing for fear of introducing oxygen. I just rack to a keg that’s been flushed with CO2, hook up the gas, and “cold crash” in the kegerator. Wait a week or two, then discard the first 8 oz.
I recently added a gas post to my Blichmann conical and I have to say it works beautifully! I just connect my CO2 tank with the regulator at zero pressure and then dial in a teeny bit of pressure. No suckback when I drain the fermenter. My blowoff tube allows me to have somewhere on the order of a foot of water column on it, so I can pressurize the fermenter occassionally without having suckback.
Search for “gas ball lock bulkhead post” on Ebay to find plenty.
I decided to email support at SSBrewtech and this was their response.
Gordon,
This happens with all air tight fermenters, as the liquid cools it contracts, so it can draw in outside air or in this case sanitizer. I would recommend going to an airlock or bubbler during crash cooling, that way just air and not sanitizer get drawn into your Bucket.
No need to worry about oxidation, there is still the protective blanket of CO2 on top of the beer. Thanks!
Cheers,
Michael
So basically what he is suggesting is to use the typical three piece air-lock with no liquid inside. I will try this with my next batch and see how it goes. I typically use a blow-off tube for the first three days and then move to the airlock after the first big push.
YIKES, I would ask him for his DO reading to confirm that! You won’t catch me doing that!
Yes, thinking that there will be a layer of CO2 protecting the beer is silly and unscientific.
Indeed
Agreed. Why would you want to suck in air into the fermenter? What kind of response is that?
Thanks
There are YouTube videos showing how you can pour CO2 from a container, into another container and a candle will go out. Some think that this is due to no O2. One should not reach the conclusion that it is no O2, as combustion will not be sustained when the CO2 concentration is around 10%. I sat through many safety videos over the years that went over the dangers of gases pooling in confined spaces.
As an aside, if you ever see a video of a brewer going into a cellar with a candle, it may have been for light, but if the candle goes out, the brewer would know to turn around and get out! That clicked when watching the introductory video on the PU tour.