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

[doug293cz]

But is it? Surely removal of the oxygen would require a pump to pull a vacuum. Starting with 'air' and then pumping in CO2 and releasing with a PRV would be dilution, no?

You can reach any arbitrary O2 level just by enough dilution, assuming the diluent has a lower O2 concentration than your target O2 level.

Brew on

 

[Zadkiel]

You can reach any arbitrary O2 level just by enough dilution, assuming the diluent has a lower O2 concentration than your target O2 level.

Brew on

Of course, I don't deny that, I was mostly objecting to the statement that using a hop bong was removing all oxygen when I realised that wasn't true..

It's got me wondering though, just how effective is that process with a hop bong? I started to try and do the maths but then I read up documentation on how to use a hop bong and discovered that you're holding the CO2 line 'open' not only while the bong pressurises but also while you pull the PRV valve, and that makes the maths a nightmare as it's partially dependent on how long you hold the PRV open for, flow rates, and more.

 

[mac_1103]

I started to try and do the maths but then I read up documentation on how to use a hop bong and discovered that you're holding the CO2 line 'open' not only while the bong pressurises but also while you pull the PRV valve, and that makes the maths a nightmare as it's partially dependent on how long you hold the PRV open for, flow rates, and more.

So close the valve between cycles instead and the math is doable.

 

[worlddivides]

I can't say you are totally wrong but you are not totally right either. Oxidation is a perpetual process. Your starting point determines a lot of the outcome. Let me explain...

If you brewed a totally no-oxygen beer, your starting point would be all malt flavor and no oxidation flavor. In contrast, if you brewed a splishy splashy oxygen fireball, your starting point point would be filled with oxidation flavor.

Remember that another homebrew myth is that oxidation = cardboard. In reality, oxidation starts very subtle and grows in intensity given the right circumstances. So as brewers, were are just trying to limit the negative circumstances. But, until one brews a beer with low oxygen process', the starting point will already have plenty of oxidation flavor baked in. In my view, this leads to folks saying they have never experienced oxidation flavors. Well, the flavor is already there and often gets associated with malt sweetness. The distance from the flavor being present to cardboard can be long.

Limiting oxygen gets associated with NEIPAs and other hop forward beers because the loss of hop aroma due to oxygen can be quite obvious. But the same factors are at work with malt flavor as well.

I have tasted noticeable oxidation in: beer in growlers (particularly if they are only half filled), in beer by other homebrewers (especially relatively newer homebrewers), in wine that has been open for a certain period of time (especially if it's stored at room temperature after opening), and spirits that are pretty old and have had a lot of air in them for a long period of time.

But that's why I always added "noticeable" and never claimed that none of my beers had any oxidation. They just didn't have any that I could perceive. I mainly just gauge it off of the color, the smell, and the taste with reference with how it's "supposed" to taste.

 

[Zadkiel]

So close the valve between cycles instead and the math is doable.

But what's the point of that if that's not how people use it? I'm curious if a hop bong actually reduces the O2 ingress under 'normal' use to a viably low concentration, or if everyone's been blindly accepting that it does.

The maths is very much NO if you close the CO2 while opening the PRV - the fermzilla doc says to set the CO2 to 10PSI and cycle the PRV 3 times. If you were closing the CO2 when opening the PRV then there's still about 4.5% O2 inside the bong after 3 cycles when you open it to the fermenter. But if you're leaving the CO2 open on 10PSI and holding the PRV open for a few seconds each time, I have no idea how to even start calculating that.

 

[mac_1103]

We know that you can dilute the oxygen to extremely low concentrations by repeated purge cycles of pressurization and release. Why would we worry that leaving the CO2 flowing while you pull the PRV would make it work less well?

 

[Zadkiel]

We know that you can dilute the oxygen to extremely low concentrations by repeated purge cycles of pressurization and release. Why would we worry that leaving the CO2 flowing while you pull the PRV would make it work less well?

No, the point is that makes it work better, much better, but it also makes it too hard to actually calculate how much O2 is still in there. Calculating it with the valve closed makes the maths easy, but it also makes the amount of O2 left inside bad, very bad

 

[mac_1103]

Calculating it with the valve closed makes the maths easy, but it also makes the amount of O2 left inside bad, very bad

Not if you do the number of cycles that the math tells you to.

 

[Zadkiel]

Not if you do the number of cycles that the math tells you to.

It would be hundreds of cycles. You're starting with 21% O2 and at 10PSI on the CO2, you're only reducing the O2 by 40% each cycle.

 

[mac_1103]

20 cycles at 10 PSI leaves 6.53 ppm oxygen. 25 cycles leaves less than 1 ppm.

 

[Zadkiel]

maybe you think I'm curious for my own benefit, that I'm using a hop bong and trying to work out a process for myself. No, I'm still in plastic buckets - any bong in my house isn't going to have hops in. For me this is an academic excercise, I wanted to work out whether the 'standard' hop bong process that other people use was actually effective, then started working out the maths and realised that because people leave the CO2 line open while opening the PRV, that makes it too hard for me to work out.

it's 2am here and my head hurts. speak again tomorrow, nn!

 

[kohalajohn]

I don't think a vacuum is required.

Imagine you have a hose filled with gas A. At one end of that hose you connect gas B. And gas B is at high pressure and flows through the hose. Gas B will eventually push out all of gas A.

This is what happens in my hop bong. The prv valve at the top of the bong is open. At the bottom of the bong I connect co2. For one minute I introduce co2 at low pressure.

Over a minute, the co2 pushes all of the atmospheric gas in the bong, out through the top prv.

Doug can explain this better than I can, but:

Yes, at first, diffusion happens. In the first few moments, the combined gas coming out the top prv is say 50% gas A and 50% gas B. Then it drops down to 1% gas A. Then .1% and so on until gas A is so virtually zero that we may as well call it zero.

I can guess that this benefit happens because the transport of the gases is happening faster than diffusion is happening.

Same thing with fermentation gas bubbling up and pushing out the pre existing air in the fermenter ullage, out through the gas lock. Eventually all the oxygen is pushed out. In this case the massive amount of time is the winner. One hundred hours of fermentation will overcome any diffusion effects.

So you are right, diffusion is happening. But it loses out to the vastly more effective factor of transportation.

 

[Zadkiel]

Over a minute, the co2 pushes all of the atmospheric gas in the bong, out through the top prv.

That's completely different to how I understood they are used, when I've watched videos on people using a hop bong, I've seen them add the CO2, then pull the PRV for a few seconds, release it to build up CO2 pressure again, pull the PRV for a few seconds, then repeat a 3rd time.

Have I been mislead by those videos?

like this (video is linked to a timstamp):


edit: OK, I'm really really done for tonight, wife is getting angry at me for not coming to bed.

 

[VikeMan]

Limiting oxygen gets associated with NEIPAs and other hop forward beers because the loss of hop aroma due to oxygen can be quite obvious.

Not to mention the brown/purple color.

 

[VikeMan]

In reality, you need an O2 meter that can resolve down to 0.01 ppm, since the target total dissolved O2 is ~0.1 ppm.

I shudder to think what dissolving O2 to a full 1.0 ppm would taste like. Or actually, I suppose it would taste fine, for a little while.

 

[VikeMan]

Ok, there is a situation where co2 is an effective blanket. Sort of.

The wine stores sell pressurized bottles of wine preserver. It is argon with some carbon dioxide. If you have wine left in the bottle after dinner, you insert the thin tube into the bottle and inject a couple inches of inert gas.

This is similar to purging a keg with CO2 (though not under pressure/release cycles in the case of the wine gadget). The process (of dilution) and the math are well known, but it has nothing to do with CO2/Argon forming any type of blanket.

In a sense, it's the fact that CO2/Argon is not a blanket (i.e. freely mixes with other gases) that allows the wine gadget to work the way it does.

 

[VikeMan]

But I think the exception is the hop bong concept. That is not dilution. That is removal of all oxygen in the vessel.

Hop Bongs (I must be old...they were mostly called hop droppers when I was building them) don't remove any gases from the fermentation vessel. They do dilute (but don't remove all of) the O2 in the dropper itself. That said, they can be used to reach very, very low levels, depending on how much CO2 you're willing to use.

 

[mac_1103]

That's completely different to how I understood they are used

Different products come with different instructions for use. Some say to flush with CO2 at 1-2 PSI continuously for 60 seconds.

 

[kohalajohn]

That's completely different to how I understood they are used, when I've watched videos on people using a hop bong, I've seen them add the CO2, then pull the PRV for a few seconds, release it to build up CO2 pressure again, pull the PRV for a few seconds, then repeat a 3rd time.

Have I been mislead by those videos?

like this (video is linked to a timstamp):


edit: OK, I'm really really done for tonight, wife is getting angry at me for not coming to bed.

That's how Kegland says to do it. @Bobby_M sold me the bong and his advice was to do it with the prv open and a constant flow, so that is what I do.

We are guessing here, as we can't see what is happening. But Bobby's method makes sense to me.

 

[kohalajohn]

Hop Bongs (I must be old...they were mostly called hop droppers when I was building them) don't remove any gases from the fermentation vessel. They do dilute (but don't remove all of) the O2 in the dropper itself. That said, they can be used to reach very, very low levels, depending on how much CO2 you're willing to use.

Perhaps "Dilution down to below sensory levels" is the phrase we should use.

Ok, I have to get off this site and read a book.

 

[Pennine]

I'm sensing a bit of O2 neurosis here.

 

[Bassman2003]

I have a fermentation purge gas set up as well as a separate keg for dry hopping. I hook up my hop bong to the dry hop keg and put it in-line between the fermenter and serving keg. This way all of the fermentation gas purges the dry hop keg and hop bong. I then transfer the carbonated (spunded) finished beer into the dry hop keg and close everything up. I then hook up CO2 gas to the bottom part of the hop bong with a small flow active and unscrew the top post from the hop bong. This leaves the top threaded part open which I quickly insert a funnel and add all of my hops. I then screw the post back on, purge some then pressurize for the drop.

This is designed to start with low to zero oxygen before opening for hops and then minimizing the opportunity for O2 ingress before purging back out. Not perfect but better then other alternatives.

 

[kohalajohn]

That's a good system.

For me, rather than use a hop bong, I have been using a hyperbaric chamber. I crawl inside the chamber, bringing the fermenter with me. I have the chamber filled with co2.

When I open the fermenter and add the hops, the entire environment is co2, so there is zero oxygen ingress.

I am wearing scuba gear so I can breathe in the chamber.

Photo attached.

 

[Bassman2003]

Livin' the dream!

 

[mashdar]

Yes, yeast goes into anaerobic fermentation mode once the O2 is gone (it has no other choice), but the fact that we can repitch yeast demonstrates that yeast can return to aerobic fermentation mode when reintroduced to O2 in the presence of food (fermentable sugar.) I am by no means a yeast metabolism expert, but it seems reasonable that yeast will at least partially revert to some aerobic activity if O2 becomes availalble in the presence of fermentable sugar.

Brew on

I think the biggest question is: will the yeast remain active until the O2 is either purged or consumed? I flip flop on this regularly -- It takes a lot longer for the headspace to clear by O2 diffusion into the liquid than displacement during strong fermentation. As you said earlier in this discussion, this is because the equilibrium point for gaseous O2 will be significant until consumption or oxidation reduces liquid O2 vapor pressure enough to allow more diffusion.

Can yeast form significant mass of sterols without available food? Maybe?

 

[doug293cz]

I would like to think that the people designing and marketing hop bongs would have their recommended chamber purging methods tested by someone with sensitive O2 meters, and then have done calculations for typical use cases that showed the contribution to total dissolved O2 would be insignificant (less than 0.05 ppb.)

Brew on