cold side oxidation - dry hopping - pressure fermentation

[nathanscrivener]

Hi guys, this is not quite a LODO question, but probably the right place to ask this.

I have the ability to ferment under pressure. My current method to dry hop is to throw pellets in the top after chilling. At this stage the beer is already carbonated. I then purge the headspace a few times to minimise any oxygen.

Does anybody know if the ability for beer to absorb oxygen is affected by whether it has been saturated with co2? I wonder whether there would be less oxygen pickup in this scenario compared to uncarbonated beer.

 

[RPh_Guy]

Carbonation does not prevent oxygen from dissolving and therefore does not prevent oxidation.

 

[nathanscrivener]

Carbonation does not prevent oxygen from dissolving and therefore does not prevent oxidation.

Do they not compete in any way? I’m interested in a bit more of an explanation if anyone can help

 

[Vale71]

https://en.wikipedia.org/wiki/Partial_pressure

 

[nathanscrivener]

https://en.wikipedia.org/wiki/Partial_pressure

Thank you. Although I am still confused. I’ve looked through that article and can’t see where that addresses my question.

 

[Vale71]

Towards the end you'll find the section on the solubility of gases. Here is the main Wikipedia article. The rest gives you background information that is still useful.

 

[RPh_Guy]

Do they not compete in any way?

No, at least not enough to be helpful.

As per the LOB methodology, dry hopping toward the end of fermentation and then closed transferring to a purged keg with enough residual extract to carbonate (AKA spunding) is the ideal method to avoid oxidation during packaging.

Hope this helps!
Cheers

 

[nathanscrivener]

This is interesting reading, again I don’t profess to have sufficient chemistry knowledge to understand this but it seems to indicate that it is likely that where you have a solution that is saturated with one substance, it will affect the solubility of another.

https://chemistry.stackexchange.com...bstances-be-dissolved-in-a-saturated-solution
In the case described here, the beer is super saturated with co2, because has been held under higher than atmospheric pressure, and you have to depressurise in order to take the lid off to add hops.

 

[RPh_Guy]

This is interesting reading, again I don’t profess to have sufficient chemistry knowledge to understand this but it seems to indicate that it is likely that where you have a solution that is saturated with one substance, it will affect the solubility of another.

https://chemistry.stackexchange.com...bstances-be-dissolved-in-a-saturated-solution
In the case described here, the beer is super saturated with co2, because has been held under higher than atmospheric pressure, and you have to depressurise in order to take the lid off to add hops.

Like I said, not enough to be meaningful.

Let's say the headspace is 100% CO2 after fermentation. You then open the vessel to add hops and purge with CO2. Now let's say the headspace is 95% CO2 and 5% air. What happens? Assuming equal pressure, a negligible amount of CO2 will indeed diffuse out of the beer and into the headspace, but more importantly, The oxygen from the 5% air in the headspace will diffuse into the beer. CO2 dissolved in the beer does not prevent this; gases do not behave like solids.

 

[Vale71]

What applies to solid solutes does not generally apply to gaseous solutes. If you expose carbonated beer to atmospheric oxygen it will start to absorb it until O2 reaches the saturation level corresponding to its own partial pressure. This obviously takes time and it won't happen at all if you just quickly open and close the vessel and then thoroughly purge the headspace of any trapped O2, which will use up lots of CO2 BTW. The problem is it takes very little oxygen cold-side to quickly affect beer.

 

[isomerization]

I noticed a substantial improvement in my hazy IPAs (shelf life/color and clarity in hop aroma being the biggest two) when I switched to a pressurized fermenter, dropped the yeast with a soft crash and then added dry hops with CO2 turned on while the PRV was open.

Obviously, some O2 was mixing in from the act of physically introducing the hops through the stream of CO2 being blown out. Always open to improving processes, but this has helped quite a bit, so good for now.