i will say the same as i did to the other guy.
so do you purge your fermenter every time you open it to check gravity? Because you are basically saying that if you dont, all your beer is now oxidized. Every time you open your fermenter.
It takes time for diffusion to happen, the OP says that he opened it briefly. As in seconds. Not for a day
I don't open fermenters to take gravity readings. I used to remove the air-lock from the bucket lid and pull a sample using a straight piece of rigid tube. I used a refractometer to check for fermentation endpoint, so only needed a few drops for a sample. Currently I use a
Tilt wireless hydrometer to monitor fermentation, so there is no need to even remove the airlock to sample. I have also switched from bucket fermenters to PET wide-mouth jar fermenters to reduce air ingress (primarily due to the iffy seal around bucket lids.) With the new fermenters, I can do a pressurized transfer from the fermenter to a pre-purged keg (liquid method) to avoid air exposure during the transfer. The weak point I still have is air suck-back thru the airlock during cold crashing. I plan to eliminate this exposure by getting a 6.5 gal corny keg, and transferring to it prior to completion of fermentation, and then finishing with a pressurized (via spunding valve) fermentation and cold crash in the keg. At this point, my wort will never be exposed to the atmosphere after initial oxygenation in the fermenter.
As the video demonstrates, the time frame for complete interdiffusion is minutes, not days, and you don't need complete interdiffusion to have too much O2 in the headspace. As @jddevinn pointed out, the amount of air that enters a vessel when opened is dependent on the area of the opening. A carboy is much better than a bucket, and a keg is somewhere in between those two. OP asked about opening up a keg, and the removal and replacement of a keg lid adds a significant amount of convection to the equation. Convection mixes gases orders of magnitude faster than diffusion alone. Thus a keg will definitely contain enough O2 after opening to adversely affect the beer over time. Exactly how much O2 is impossible to determine a priori. If you don't have the ability to measure ppb levels of O2 in the keg, then the only safe option is to purge for the estimated worst case, and that is the analysis I presented in a previous post.
The fact that you seem to not like the science does not invalidate the science. If you expose your beer to O2 post fermentation, you will get some amount of oxidation. The more O2, the more oxidation. Temperature plays a big role in the rate of oxidation, so colder beer takes longer to reach the same level of oxidation as warmer beer.
If you are happy with how your beer tastes over its entire lifetime, then you don't need to make any changes to your procedures. Different people have different taste thresholds for oxidation effects. If yours is high, then you don't need to be as careful.
When people ask about best practices, or underlying science, I will attempt to provide the best information available (as I understand it), assuming I have some expertise in the area of interest. What anyone does with the information is up to them. I only try to educate, not proscribe behavior.
Brew on
