Estimating O2 exposure and number of purges needed

[Hannabrew]

In another thread, I mentioned my process of dry hopping in a keg which consists of performing a closed transfer to a fully CO2 purged keg, opening the lid, quickly dropping my loaded SS hop container in there, quickly closing the lid and then purging with CO2 about 4-5 times at around 30 PSI.

303Dan mentioned that this might not be enough and presented the below graph which I had never seen before.

This graph appears to be assuming that you start with regular air and no CO2. My question is, with the scenario above, how much O2 would you suspect I am introducing with the short exposure to air when I add the dry hops? Secondly, how does this graph's slope change if the starting point is much lower?

Basically just trying to understand how many purges I should be doing to try to get my oxygen level as close to .1 as possible.

 

[303Dan]

Here's an idea I just thought of. It doesn't answer your question, but maybe addresses the concern.

Assuming you are opening the lid for only a short period of time, you could connect your co2 to your fully filled and purged keg at a very low pressure, like 2psi. Then remove the lid and immediately turn on the gas and leave it going for the 10-15 seconds or whatever it takes to drop in your dry hop and replace the lid. That would theoretically create positive pressure pushing out the top of the keg and I would think prevent the mixing of air into the headspace while the lid is open without wasting too much co2.

Thoughts???

I'd still like to hear the answer to the question you asked.

Dan

 

[hezagenius]

You will definitely be introducing some O2 if you open the lid. Hard to say how much really. Too many variables to account for.

Are you filling the keg with sanitizer and flushing that out with CO2 prior to filling? If you are just purging by adding CO2, venting, adding CO2, venting, etc, then you could add the hops first, then add CO2 and vent several times, then do your closed transfer.

If I ever have to open the lid to add hops or something, I put the lid back on and purge 5 times at serving pressure. I've never had an oxidation problem.

I've been racking my brain to come up with a solution for adding hops to a keg without introducing O2 but I can't come up with anything.

 

[Hannabrew]

You will definitely be introducing some O2 if you open the lid. Hard to say how much really. Too many variables to account for.

Are you filling the keg with sanitizer and flushing that out with CO2 prior to filling? If you are just purging by adding CO2, venting, adding CO2, venting, etc, then you could add the hops first, then add CO2 and vent several times, then do your closed transfer.

If I ever have to open the lid to add hops or something, I put the lid back on and purge 5 times at serving pressure. I've never had an oxidation problem.

I've been racking my brain to come up with a solution for adding hops to a keg without introducing O2 but I can't come up with anything.

I do push out sanitizer to fully flush.

 

[hezagenius]

This also doesn't answer your question but here's something else that I do to try to work around O2 exposure for my NEIPAs:

Ferment normally for 4 days (adding dry hops on day 2 into the primary)
At this point, fermentation is slowing down but still active
Add hops to an empty dry hop keg
Do a pressure transfer from the fermenter to the dry hop keg (I don't bother purging this keg but it wouldn't hurt)
Purge the keg 5 times at 15psi
Hook up a blowoff tube to a gas QD and put that on the gas post
Let it continue to ferment for 2 days with the blowoff tube connected
My hope is that this purges the remaining O2 that was left in the keg
On day 6, hook up a spunding valve set to 5 psi for a few days until FG is reached
Once FG is reached, remove the spunding valve
Hook up the CO2 and apply 15psi and cold crash for 2+ days

Add sanitizer solution to serving keg. Fill it as full as possible.
Flush out the sanitizer solution through the liquid post
Flip the keg over and while adding some CO2 pressure, gently pull the PRV to release the remaining sanitizer
Once it blows air, you have a purged keg and can do a pressure transfer from the dry hop keg to the serving keg


It's probably overkill but that's part of the fun of homebrewing.

 

[hezagenius]

I know at the commercial level, some tanks have chambers where you can add things, flush it with CO2 to purge the O2 and then release the additions into the main section of the tank. We need that for homebrew kegs!

 

[Weezy]

Id like to do a taste test of two beers, both closed loop fermentation in a keg and self transfer to two serving kegs. Keg 1, purged only by 4 fills/releases at 15-psi after beer is transferred. Keg 2, initially purged by vacating water with CO2, then 10 fills/releases at 30 psi after beer is transferred. See how much they differ.

 

[dyqik]

I know at the commercial level, some tanks have chambers where you can add things, flush it with CO2 to purge the O2 and then release the additions into the main section of the tank. We need that for homebrew kegs!

Hmm. Jaybird (norcalbrewingsolutions) sells things like mason jar to triclover adapters and other custom bits and pieces, and I'm sure he could knock up a keg lid with triclover attachment. You could weld a triclover to a keg lid, attach a butterfly or ball valve to seal it, and purge/transfer to the keg as normal. When it's time to dryhop, add a triclover tee or cross with a gas inlet and outlet on the cross arm to the other side of the valve. Pour dry hops into the tee/cross on top of the valve, and cap the top. Purge the triclover fitting/hops with CO2, before opening the ball valve to dump the hops in.

Basically it'd be the same as triclover yeast harvesting fittings for conicals, but on the top and upside down.

If you then transferred to a serving keg after dry hopping (with a hop blocker on the liquid out diptube), you'd only need one keg lid adapted that way.

 

[dyqik]

You could also use a purged Randall and a diaphragm pump to dry hop in a closed loop by recirculating beer from a keg through the hops. You wouldn't need as long a dry hop that way either.

 

[Hannabrew]

Id like to do a taste test of two beers, both closed loop fermentation in a keg and self transfer to two serving kegs. Keg 1, purged only by 4 fills/releases at 15-psi after beer is transferred. Keg 2, initially purged by vacating water with CO2, then 10 fills/releases at 30 psi after beer is transferred. See how much they differ.

I think the real test is how do they taste after some time has passed and any potential oxidation has had time to do it's thing

 

[Weezy]

I think the real test is how do they taste after some time has passed and any potential oxidation has had time to do it's thing

Yes. Very true. But it'd be worth doing before spending $100+ on equipment to solve a hypothetical problem.

 

[JasonG]

I have been struggling with this ever since the LoDo information started circulating. I have always struggled to make IPAs I was happy with, and eventually I decided that it was cold side oxygenation I was dealing with. I have typically done a double dry hop on my IPAs.

What I did on my most recent batch worked well, probably the best IPA I've made. I'm sure plenty of others have adopted a similar technique.

I have started pitching my first dry hop about 3 days into primary ferment, when there is still a fair amount of air lock activity. After 5 days, when fermentation has slowed but not stopped, I transfer. I use my planned serving keg, fill with iodophor most of the way. I remove the quick disconnect, poppet, and dip tube from the gas in port, put the lid on the keg, and siphon more iodophore in through the beer out QD. I keep the keg at an angle, so the gas in port is at the highest point. I pop the pressure relief valve, and wait for sanitizer to come out through the port, then close it. I then wait until sanitizer runs out through the gas in port. I rock the keg back and forth until all the air has come out. I then stop the siphon, and place the dip tube, poppet, and a quick disconnect with an open barb back on. I then restart the siphon and let sanitizer run out through the gas in disconnect, and rock it again to be sure all the air is out. By this time, I figure I have removed the vast majority of air.

I then push out the iodophor through the beer out port. Now I figure I have a nearly purged keg. I connect the gas through the beer out port and turn it on at about 5 PSI and let it run. I then open the lid, and place the second set of dry hops in a hop bag into the keg. I put the lid back on (CO2 running), and purge at 30 PSI - I think I did 10 purges the last time.

Then, I run the beer, which still has some active fermentation going on, from my Speidel into the keg. I do the same process of putting the keg at an angle and rocking back and forth, until beer comes out the gas in port with no air, and stop the siphon.

I hooked up to gas, and pushed out a bit of beer from the beer out side. I then pressurized to about 3 PSI, took off the pressure relief valve, and added in about 1/4 of the recommended amount of table sugar to keg carbonate. I did this using a large (30mL) syringe, and injecting a preboiled and cooled water/sugar solution through the PRV opening. In my mind, the sugar with the active yeast in suspension would help make sure that whatever O2 was picked up, would hopefully get consumed by the yeast. I was hopeful that this process would not add much oxygen when adding the sugar, but I'm not really sure if it is worth the potential trade off.

I left it at about 68F for 5 days (some time for yeast to work, but not necessarily trying for a fully carbonated keg), then chilled and forced carbonated with CO2. By about 1 week it was tasting great, and has held up fairly well for about 6 weeks now, only losing a bit of the aroma so far.

This may be overkill, and I do not have a DO meter to measure, but this process worked really well for me last time.

Sorry, this post in no way answers your question, but maybe you'll find it useful.

JG

 

[thekraken]

Here's an idea I just thought of. It doesn't answer your question, but maybe addresses the concern.

Assuming you are opening the lid for only a short period of time, you could connect your co2 to your fully filled and purged keg at a very low pressure, like 2psi. Then remove the lid and immediately turn on the gas and leave it going for the 10-15 seconds or whatever it takes to drop in your dry hop and replace the lid. That would theoretically create positive pressure pushing out the top of the keg and I would think prevent the mixing of air into the headspace while the lid is open without wasting too much co2.

Thoughts???

I'd still like to hear the answer to the question you asked.

Dan

Correct me if I'm wrong but I think this just about what @schematix does with his dry hops for his LoDo method. I've been planning to do exactly this here in the next day or two.

 

[Hannabrew]

Correct me if I'm wrong but I think this just about what @schematix does with his dry hops for his LoDo method. I've been planning to do exactly this here in the next day or two.

If so, I like this method best as it's not much different than what I already do and requires just a tad more CO2.

 

[303Dan]

Correct me if I'm wrong but I think this just about what @schematix does with his dry hops for his LoDo method. I've been planning to do exactly this here in the next day or two.

I'm not familiar with what that guy does, but if you try this approach, I'd love to hear how it goes. I was fairly certain I wasn't the first person to think of it.

Dan

 

[doug293cz]

...

This graph appears to be assuming that you start with regular air and no CO2. My question is, with the scenario above, how much O2 would you suspect I am introducing with the short exposure to air when I add the dry hops? Secondly, how does this graph's slope change if the starting point is much lower?

Basically just trying to understand how many purges I should be doing to try to get my oxygen level as close to .1 as possible.

I am the source of that chart. The equation that determines O2 concentration is:

Final_O2_Concentration = Starting_O2_Concentration * (14.7 / (14.7 + Purge_Pressure)) ^ Purge_Count​

The amount of O2 that "sneaks" in while the lid is open is not determinable. If you flow CO2 while the lid is open, you want to have a flow rate that will give you a flow velocity out of the lid of at least 50 linear feet per minute. This flow rate is based on design specs for chemical fume hoods that require 100 feet/min face velocity to prevent toxic fumes from diffusing back into the room.

Brew on

 

[Hannabrew]

Thanks for the reply and for the graph. Assuming we're using a standard lid on a corny, what would be your best guess at the PSI needed to come close to that velocity?

 

[ajdelange]

I don't think the second question has been answered yet. The vertical axis is a log scale so the numbers are ratios. Thus for 30 psig you dispose of about 69% of the remaining air on each cycle of purge from whatever the starting point. Starting at 1 atm the numbers are approx. 0.316 atm, 0.1 atm, 0.0316.... Starting at 0.2 atm they would be 0.0632, 0.01, 0.00632, 0.001...

 

[Hannabrew]

I don't think the second question has been answered yet. The vertical axis is a log scale so the numbers are ratios. Thus for 30 psig you dispose of about 69% of the remaining air on each cycle of purge from whatever the starting point. Starting at 1 atm the numbers are approx. 0.316 atm, 0.1 atm, 0.0316.... Starting at 0.2 atm they would be 0.0632, 0.01, 0.00632, 0.001...

Thanks AJ. When you say 1 ATM, is that the same as 1 PPM O2? Sorry if that is a dumb question!

Isn't the amount of O2 that is let in during a quick opening and closing of the keg lid for x seconds measurable by somebody with an DO meter? It would be great to know approx how much O2 we're letting in and get a rough idea of how many purges are needed to expel it.

 

[ajdelange]

Thanks AJ. When you say 1 ATM, is that the same as 1 PPM O2? Sorry if that is a dumb question!

One atm is 1 atmosphere which is 14.7 psig. It doesn't matter what the units are. If you have 100 ppm O2 in the headspace you will have 10 after two changes at 30 psig (when things equilibrate).

Isn't the amount of O2 that is let in during a quick opening and closing of the keg lid for x seconds measurable by somebody with an DO meter?

With a meter that measures headspace gas. It could also be done with a liquid measuring meter but that would take quite of bit of additional effort.

 

[Hannabrew]

With a meter that measures headspace gas. It could also be done with a liquid measuring meter but that would take quite of bit of additional effort.

oh yeah...I guess I was assuming the O2 gets in the beer right away which is not the case.

 

[doug293cz]

Thanks for the reply and for the graph. Assuming we're using a standard lid on a corny, what would be your best guess at the PSI needed to come close to that velocity?

Required pressure is a tricky thing to determine because you need to know the flow resistance, which will be different for all systems. We can estimate required flow volume however.

The lid opening is about 3.825" x 3.125" and (at least close to ) elliptical in shape. The opening area is about 9.39 in^2. We are looking for a "face" velocity of 50 ft/min or 600 in/min, so the volumetric flow rate needs to be 9.39 * 600 = 5633 cu in/min. This equals 24.4 gal/min or 92.3 L/min. These are pretty high flow rates.

Brew on

 

[schematix]

I'm not familiar with what that guy does, but if you try this approach, I'd love to hear how it goes. I was fairly certain I wasn't the first person to think of it.

Dan

Link to my process is in my signature. I just pieced together a bunch of really good ideas that i gathered from years of experience along with findings around the internet. I think it results in a fairly inexpensive, yet highly effective low oxygen fermentation and packaging system.

Positive pressure purging is a useful tool for adding dry hops, as well as a dose of priming sugar if doing natural carbonation. if you don't introduce oxygen, you don't have to dilute it through repeated purge cycles.

 

[Hannabrew]

Thanks Doug/Schematix...all great info.

Just did my closed transfer tonight and think it went well.

First I hooked up my CO2 tank to the fermenter and pumped a few PSI into the fermenter to get things going and then ran a gas jumper from my 99.98% CO2 purged keg to the fermenter to counter pressure fill the keg (along with the help of gravity).

Once the fermenter was empty, I hooked up the Co2 tank to the keg and pumped in 10 PSI while I got my dry hops ready.

Once the hops were in my SS tube I shut off he co2, released the pressure, popped the lid, and then turned the c02 back on at 10 psi while i added the hops and shut the lid.

The lid sealed quickly obviously since it was under pressure but a starsan test proved it was leaking. I turned the co2 to 3 psi, shut it off temporarily so i could get the lid reseated, and then turned it on once it was in position. Once it looked good I cranked to 40 psi and did another leak test which was successful.

I have no idea how much O2 is in there but I know its less than my normal process and that can't hurt.

Thanks for the advice!

 

[ajdelange]

Clearly the best way to purge a keg is to push out all the air with something else. I use steam, others use sterilized water and, of course, there is beer. Assuming you have a purged keg which you have filled with beer and then wish to add hops (unless you are using extract) you must open it thus admitting air. This air will have a few sec to work its evil but it could be pushed out thorough the pressure relief valve with beer from another keg. Done right losses should be small. After pushing all the air out you would probably want to draw some beer through the dip tube so you have some headspace. At this point the beer should be drinkable so that beer would not be lost either.

 

[thekraken]

Clearly the best way to purge a keg is to push out all the air with something else. I use steam, others use sterilized water and, of course, there is beer. Assuming you have a purged keg which you have filled with beer and then wish to add hops (unless you are using extract) you must open it thus admitting air. This air will have a few sec to work its evil but it could be pushed out thorough the pressure relief valve with beer from another keg. Done right losses should be small. After pushing all the air out you would probably want to draw some beer through the dip tube so you have some headspace. At this point the beer should be drinkable so that beer would not be lost either.

AJ, I'd like to know more about how you purge with steam if you wouldn't mind sharing some details.

 

[ajdelange]

I brew with steam. When the boiler was installed the guy I got to do it said to me "Ya doing crabs?" I said "No, why?" and he responded that he owned a crab house and that was the same boiler they used to which I said "hmmm", installed a culinary steam filter and have had many a tasty crab, lobster and sausage out of it. In any case there is, from the filter, a brewers/vintners hose with a triclover flange on the end which connects to my crab pot (repurposed brewing kettle) and to anything else triclover which includes (with adapters) a standard Sankey coupler with pea and checkvalve removed and some valves (Micromatic) installed. This makes it easy for me to run steam thru a keg for 15 minutes which I figure gets all the air out. I then shut off the steam, remove the coupler and pop on one connected to a CO2 tank set for 3 atm. As the steam collapses it is replaced by CO2. Blow down the condensate and I have a sanitized keg full of CO2 @ a couple of atm. all ready to counter-fill.

I can't see how you would adapt this to Cornies but I guess conceptually at least it's possible.