Best practice for purging headspace during/after dry hop

[CyberFox]

I ferment and dry hop in a corny keg with a floating dip tube. I'm planning to make a beer with 24 oz of hops (12 oz hop stand and 12 oz dry hop), so I REALLY don't want to mess it up with oxidation. My plan is to continuously purge the headspace with CO2 while adding the dry hops, then do more purging after sealing it up. I'd like to hit the best balance between maximizing the shelf life of my beer and saving CO2. Here are my questions:

1) What PSI should I aim for when doing the continuous purge?
2) What PSI and how many purges should I aim for after sealing the keg back up?

Please let me know what you recommend. Also, let me know if you can think of a better plan with my setup. Thanks in advance!

 

[day_trippr]

So, the plan is to cram 12 ounces of hops in a single keg? Woof!
It's not so much pressure as volume. A few psi for a long time will do, higher psi could shorten the time I suppose but the volume might end up the same. If you don't mind blowing a crapton of CO2 in the gas post and out the PRV that's what I'd do. Have everything ready, pop the lid, cram in the pellets, lid it up, then blow CO2 through the keg...

Cheers!

 

[doug293cz]

I ferment and dry hop in a corny keg with a floating dip tube. I'm planning to make a beer with 24 oz of hops (12 oz hop stand and 12 oz dry hop), so I REALLY don't want to mess it up with oxidation. My plan is to continuously purge the headspace with CO2 while adding the dry hops, then do more purging after sealing it up. I'd like to hit the best balance between maximizing the shelf life of my beer and saving CO2. Here are my questions:

1) What PSI should I aim for when doing the continuous purge?
2) What PSI and how many purges should I aim for after sealing the keg back up?

Please let me know what you recommend. Also, let me know if you can think of a better plan with my setup. Thanks in advance!

1) What is actually important is the linear velocity of the CO2 coming out of the opening used to add the dry hops. Linear velocity is the flow rate in cubic feet per minute divided by the area of the opening (in sq ft.) You want the velocity to be greater than 50 ft/min. (Safety specs for hazardous vapor fume hoods require designing to a face velocity of 100 ft/min - a 2x safety factor.) You'd need a gas flow meter to do this right.

2) Number of purges is dependent on the pressure used.

If you flow gas while the vessel is open, then your starting point will not be the top of the table, but somewhere further down. Estimating starting O2 ppm in this instance is not really possible for the general case. You'll just have to guess, but if you follow the 50 ft/min face velocity advice, I would think it safe to assume you are starting with less than 1000 ppm O2. Lower purge pressures take more cycles, but use less gas overall.

Brew on

 

[CyberFox]

1) What is actually important is the linear velocity of the CO2 coming out of the opening used to add the dry hops. Linear velocity is the flow rate in cubic feet per minute divided by the area of the opening (in sq ft.) You want the velocity to be greater than 50 ft/min. (Safety specs for hazardous vapor fume hoods require designing to a face velocity of 100 ft/min - a 2x safety factor.) You'd need a gas flow meter to do this right.

2) Number of purges is dependent on the pressure used.

View attachment 819807View attachment 819806

If you flow gas while the vessel is open, then your starting point will not be the top of the table, but somewhere further down. Estimating starting O2 ppm in this instance is not really possible for the general case. You'll just have to guess, but if you follow the 50 ft/min face velocity advice, I would think it safe to assume you are starting with less than 1000 ppm O2. Lower purge pressures take more cycles, but use less gas overall.

Brew on

You're just the guy I was hoping for! So the velocity has to be greater than 50 ft/min while adding the dry hops. Since you know way more about this than the average person, how would YOU personally carry out the process of purging with CO2 while dry hopping, then purging after sealing?

 

[doug293cz]

You're just the guy I was hoping for! So the velocity has to be greater than 50 ft/min while adding the dry hops. Since you know way more about this than the average person, how would YOU personally carry out the process of purging with CO2 while dry hopping, then purging after sealing?

Can't really answer that question without knowing what equipment is available.

What I plan to try, for my next big dry hop load, is to place the hops in a sanitized keg, purge the keg with fermentation CO2, and then closed transfer the beer to the keg with the dry hops. Can decant to another purged keg if limiting hop contact time is desired.

Another method is to drop the dry hops in from a purged chamber, but that requires special equipment.

Brew on

 

[CyberFox]

I guess my plan for dry hopping will be to continuously purge the kegmenter with 4 psi through the gas post, open the lid, quickly drop in the hops and close the lid, then purge 3 more times with 8 psi. Time will tell if that's good enough to minimize oxidation.

 

[RyPA]

I always ferment/dry hop/serve out of the same keg.

What I do is place my keg near my kegerator and get a CO2 gas line ready. I rest the QD on the connector and once the keg lid is off, I connect the CO2 QD. I drop the hops in, take my iSpindel out, put the lid back in and seal it up and then purge around 10 times. My beers, mostly NEIPA 's, always retain their OJ color and taste great til the end so it is working from an anti-oxidation perspective.

 

[doug293cz]

I always ferment/dry hop/serve out of the same keg.

What I do is place my keg near my kegerator and get a CO2 gas line ready. I rest the QD on the connector and once the keg lid is off, I connect the CO2 QD. I drop the hops in, take my iSpindel out, put the lid back in and seal it up and then purge around 10 times. My beers, mostly NEIPA 's, always retain their OJ color and taste great til the end so it is working from an anti-oxidation perspective.

What pressures do you use?

Brew on

 

[sibelman]

I've been doing as Doug mentioned: hops in the keg, purge with fermentation gas and then closed transfer to the hop-loaded keg, where they stay for the life of the beer. I haven't had issues with the long contact that others say yields undesirable grassy flavors. But many have reported success with the method you've mentioned. Best of luck!

 

[RyPA]

What pressures do you use?

Brew on

My tank is set to 10psi for my kegerator, I don't adjust it for this process.

 

[CyberFox]

I always ferment/dry hop/serve out of the same keg.

What I do is place my keg near my kegerator and get a CO2 gas line ready. I rest the QD on the connector and once the keg lid is off, I connect the CO2 QD. I drop the hops in, take my iSpindel out, put the lid back in and seal it up and then purge around 10 times. My beers, mostly NEIPA 's, always retain their OJ color and taste great til the end so it is working from an anti-oxidation perspective.

How long do your NEIPAs last? I usually limit myself to one beer a day, so mine will need to last a couple months.

 

[RyPA]

How long do your NEIPAs last? I usually limit myself to one beer a day, so mine will need to last a couple months.

A 5g keg usually lasts me around a month. I'm drinking one now from the same batch pictured in my profile image and it still looks the same. I've had very good results with this, some say 10+ purges is excessive, but I prefer overkill.

 

[doug293cz]

A 5g keg usually lasts me around a month. I'm drinking one now from the same batch pictured in my profile image and it still looks the same. I've had very good results with this, some say 10+ purges is excessive, but I prefer overkill.

10+ purges is only excessive if you don't understand the math behind dilution of O2 in the headspace. There are other ways to control O2 (pre-purged kegs and closed transfers) that can minimize O2, but if you can't do those for some reason, then lots of purges is the answer.

Brew on

 

[RyPA]

10+ purges is only excessive if you don't understand the math behind dilution of O2 in the headspace. There are other ways to control O2 (pre-purged kegs and closed transfers) that can minimize O2, but if you can't do those for some reason, then lots of purges is the answer.

Brew on

I've done the pre-purged keg/closed transfer process a few times and my above process is much much easier at the cost of a bit of CO2.

With the pre-purged keg/closed transfer process you can't dry hop without introducing O2..without specialized equipment at least.

 

[CyberFox]

A 5g keg usually lasts me around a month. I'm drinking one now from the same batch pictured in my profile image and it still looks the same. I've had very good results with this, some say 10+ purges is excessive, but I prefer overkill.

That's awesome. I'd say NEIPAs are already a bit excessive when it comes to hop amounts, so I'd much rather waste some CO2 than risk ruining an expensive batch of beer.

10+ purges is only excessive if you don't understand the math behind dilution of O2 in the headspace. There are other ways to control O2 (pre-purged kegs and closed transfers) that can minimize O2, but if you can't do those for some reason, then lots of purges is the answer.

Brew on

Here's to hoping that doing a continuous 4 psi purge while dry hopping in the kegmentor, purging 10 more times with 10 psi after sealing it, cold crashing under pressure, then doing a fully closed transfer to a serving keg that was purged with CO2 from fermentation mitigates enough oxygen.

 

[sibelman]

you can't dry hop without introducing O2

You can if you put your dry hops in a keg that you then purge with fermentation gas, and then do a closed transfer into that hop-loaded keg. This does require a fermenter that holds at least a little pressure for the transfer process. And it means that dry hopping isn't taking place in the (primary) fermenter, though the transfer can occur even while some active fermentation is still going on if that's desired. There are so many possibilities.

 

[RyPA]

You can if you put your dry hops in a keg that you then purge with fermentation gas, and then do a closed transfer into that hop-loaded keg. This does require a fermenter that holds at least a little pressure for the transfer process. And it means that dry hopping isn't taking place in the (primary) fermenter, though the transfer can occur even while some active fermentation is still going on if that's desired. There are so many possibilities.

That could work..I was thinking from along the lines of a keg filled to the brim with sanitizer which is then purged with fermentation CO2, as this is more of a guaranteed O2 free keg.

 

[sibelman]

more of a guaranteed O2 free keg

Maybe. But according to calculations posted here by @doug293cz, the dilution of the receiving keg's oxygen by a full fermentation's worth of CO2 is impressive - remaining O2 is thought (though not measured) to be a few parts per billion. If his analysis is accurate, one can very effectively (if always imperfectly) purge either way.

Both methods avoid wasting using a lot of store-bought CO2 for numerous fill-and-release cycles. However, the ferm. gas method facilitates dry hopping.

In my limited experience, dry hops in the purged serving keg produce the excellent IPA floral/tropical flavors and aromas I seek - better than hops at <170°F whirlpool and perhaps even in the primary. However, folks are achieving good results many different ways.

 

[IslandLizard]

Both methods avoid wasting using a lot of store-bought CO2 for numerous fill-and-release cycles.

There's a huge difference in CO2 waste usage when purging the small (~1 qt) leftover headspace in a filled keg vs. purging a completely empty keg, which is what @doug293cz's model is based on.

I doubt many of us would have issues using 20 purge cycles at 20 psi to rid that 1 qt of headspace of O2 after dropping a dry hop bag into it.
Now the dry-hop bag itself will also contain O2... even after flushing/purging it right before dropping it into the keg. I don't see a (simple) way to prevent that.

Therefore, the ferm gas purged keg, pre-loaded with the dry hops, is an excellent solution to that. And while at it, purge 2 kegs at the same time, so you'll have a pre-purged serving keg ready to receive the dry hopped beer.

 

[CyberFox]

There's a huge difference in CO2 waste usage when purging the small (~1 qt) leftover headspace in a filled keg vs. purging a completely empty keg, which is what @doug293cz's model is based on.

I doubt many of us would have issues using 20 purge cycles at 20 psi to rid that 1 qt of headspace of O2 after dropping a dry hop bag into it.
Now the dry-hop bag itself will also contain O2... even after flushing/purging it right before dropping it into the keg. I don't see a (simple) way to prevent that.

Therefore, the ferm gas purged keg, pre-loaded with the dry hops, is an excellent solution to that. And while at it, purge 2 kegs at the same time, so you'll have a serving keg ready to receive the dry hopped beer, once it's ready.

I've heard about pre-loading a keg with dry hops or suspending a dry hop bag with magnets in the fermenter. Wonder if it would be detrimental to the hops to leave them sitting for that long temperature-wise?

 

[IslandLizard]

I've heard about pre-loading a keg with dry hops or suspending a dry hop bag with magnets in the fermenter. Wonder if it would be detrimental to the hops to leave them sitting for that long temperature-wise?

That's a good question.

It doesn't look ideal for hops being suspended in a damp fermenter for 2-3 weeks at 66-72F while several cubic feet of CO2 is moving around and through it. Pellets may endure this better than whole flowers.

 

[RyPA]

Last year I did a batch where I fermented/served from the same keg and at pitching time I used magnets to hold a muslin bag of hops up above the beer and when ready to dry hop I slid them down. I then was able to slide them back up. This allowed for a batch that never saw any O2.

Out of all the different tactics I've tried, fermenting and serving from the same keg and dry hopping as I outlined above has produced solid beers and is the easiest.

 

[11thStBrewing]

I guess my plan for dry hopping will be to continuously purge the kegmenter with 4 psi through the gas post, open the lid, quickly drop in the hops and close the lid, then purge 3 more times with 8 psi. Time will tell if that's good enough to minimize oxidation.

I followed this advice when I started and had bad results every time. Dumped multiple batches trying different purging techniques. Waste of time, IMHO. The only time I was successful I had to dry hop <48 hours after pitching yeast.

Edit: to be clear, I went beyond purging 20 times. I ran co2 for 2-3 minutes continuously purging the headspace. That’s after having co2 running from the liquid and co2 posts while the lid was off for 10 seconds. It just didn’t work well at all for me.

I ended up getting a hop bong for the All Rounder and they come out proper every time after purging it for a minute with co2. Dry hop after fermentation, right before packaging or any other time. No stress.

If you’re rocking a keg, something like this with a hop bong will give you the best results:

US $26.38 9％ Off | Corny Beer Keg Lid with 1.5 Inch Ferrule Brand New 60PSI PRV Food Grade Dry Hopper
https://a.aliexpress.com/_mLBBuk0

 

[doug293cz]

I've heard about pre-loading a keg with dry hops or suspending a dry hop bag with magnets in the fermenter. Wonder if it would be detrimental to the hops to leave them sitting for that long temperature-wise?

I believe @sibelman has tested this out:

In my limited experience, dry hops in the purged serving keg produce the excellent IPA floral/tropical flavors and aromas I seek - better than hops at <170°F whirlpool and perhaps even in the primary. However, folks are achieving good results many different ways.

Brew on

 

[doug293cz]

Maybe. But according to calculations posted here by @doug293cz, the dilution of the receiving keg's oxygen by a full fermentation's worth of CO2 is impressive - remaining O2 is thought (though not measured) to be a few parts per billion. If his analysis is accurate, one can very effectively (if always imperfectly) purge either way.

I have been told privately that the residual O2 after a fermentation gas purge has been measured using adequately sensitive analytical equipment ($$$$$), and that the results are even better than the model predicts. This is not unexpected, as the model makes worst case assumptions. I trust the individual that provided this information to me, but it is hidden behind a paywall, and I am not allowed to link to it here.

Brew on

 

[sibelman]

Wonder if it would be detrimental to the hops to leave them sitting for that long temperature-wise?

So, of course me too. This period of several weeks at ale fermenting temperature (and, without the magnet-bag-drop/slide trick, some StarSan!) can't be good for freshness. Notwithstanding, I've made my best beers this way.

That said, the hop dropper concept (into the primary, or keg with, for example, the cool widget @11thStBrewing linked to above) offers a way to use totally fresh-from-the-freezer hop pellets with low oxygen ingress.

So many choices! I love the creativity of the widget makers and HBTers in solving these problems!

 

[CyberFox]

I followed this advice when I started and had bad results every time. Dumped multiple batches trying different purging techniques. Waste of time, IMHO. The only time I was successful I had to dry hop <48 hours after pitching yeast.

Edit: to be clear, I went beyond purging 20 times. I ran co2 for 2-3 minutes continuously purging the headspace. That’s after having co2 running from the liquid and co2 posts while the lid was off for 10 seconds. It just didn’t work well at all for me.

I ended up getting a hop bong for the All Rounder and they come out proper every time after purging it for a minute with co2. Dry hop after fermentation, right before packaging or any other time. No stress.

If you’re rocking a keg, something like this with a hop bong will give you the best results:

US $26.38 9％ Off | Corny Beer Keg Lid with 1.5 Inch Ferrule Brand New 60PSI PRV Food Grade Dry Hopper
https://a.aliexpress.com/_mLBBuk0

That dry hopper is very cool. I've never seen one before. Good suggestion!

I believe @sibelman has tested this out:


Brew on

Thanks. I already saw sibelman's post. I was just saying that I've heard of those two techniques before and since they both involve leaving hops at fermentation temperature, I wondered if that would be detrimental to the hops.

So, of course me too. This period of several weeks at ale fermenting temperature (and, without the magnet-bag-drop/slide trick, some StarSan!) can't be good for freshness. Notwithstanding, I've made my best beers this way.

That said, the hop dropper concept (into the primary, or keg with, for example, the cool widget @11thStBrewing linked to above) offers a way to use totally fresh-from-the-freezer hop pellets with low oxygen ingress.

So many choices! I love the creativity of the widget makers and HBTers in solving these problems!

Hey, if it works, it works. I agree that it's pretty awesome what people come up with for making beer. There are some seriously smart homebrewers!


Here's a question for you guys: do you usually let hops warm up to room temperature before dry hopping or throw them in right from the freezer?

 

[Dog House Brew]

I always ferment/dry hop/serve out of the same keg.

I’m going this route next. I assume you ferment under pressure?
What is your dryhop dosage?
How many gallons can I ferment in my kegs?
I bought the Flotit 2.0 and figured I would do the same. I’ve never fermented like this. I don’t own a stainless conical. This seems to me to be the best for brewing any IPA w/o oxidation.

 

[RyPA]

I’m going this route next. I assume you ferment under pressure?
What is your dryhop dosage?
How many gallons can I ferment in my kegs?
I bought the Flotit 2.0 and figured I would do the same. I’ve never fermented like this. I don’t own a stainless conical. This seems to me to be the best for brewing any IPA w/o oxidation.

I highly recommend it to anyone who hasn't done it yet, I see no reason to go back to a separate fermenter.

I do not ferment under pressure unless I'm using a yeast that wants cooler than I can provide. Lately I have only been using Voss Kveik which likes it hot and it tastes good in NEIPAs so I've been sticking with it.

It depends on the recipe, my latest favorite NEIPA recipe gets 0.5oz of Galaxy/Mosaic/Citra at high krausen and then 1.5oz of each when I reach FG.

Depends on your keg, cornys I'd estimate around 4.75g and Torpedo 6g maybe 5.8? I fill and leave a few inches of headspace for the krausen. I always use a blow off tube connected to the gas-in port and have a floating dip tube (Torpedo brand) on the liquid side with a screen filter over the inlet.

 

[Dog House Brew]

Thanks, everything I need right there. I'm sure I’ll learn by the yeast and the head space. Thanks again

 

[mac_1103]

I have been told privately that the residual O2 after a fermentation gas purge has been measured using adequately sensitive analytical equipment ($$$$$), and that the results are even better than the model predicts. This is not unexpected, as the model makes worst case assumptions. I trust the individual that provided this information to me, but it is hidden behind a paywall, and I am not allowed to link to it here.

I assume this was for the single five gallon keg scenario?

 

[doug293cz]

I assume this was for the single five gallon keg scenario?

That's my understanding, since the experiment was to confirm the model.

Brew on

 

[mac_1103]

That's my understanding, since the experiment was to confirm the model.

Without giving too much away, can you tell us if the data might support updating the model?

 

[doug293cz]

Without giving too much away, can you tell us if the data might support updating the model?

I don't think there is sufficient information to update the model. To improve the model, it would have to be changed to a dynamic, rather than static, model. This would require detailed knowledge of CO2 flow rates vs. time during the fermentation, and also the detailed geometry of all the vessels and tubing involved. Way too much trouble for the benefit that would be gained.

Brew on

 

[DuncB]

I believe @sibelman has tested this out:


Brew on

I think the transfer of beer / wort into purged fermenter is the method used at Sapwood cellars as well, mentioned in a podcast by Scott or Mike, can't remember which one.

 

[CyberFox]

@doug293cz I just thought of something that you could probably help me with. I implemented the continuous purge with CO2 and purging after sealing. My beer was by far the best I've ever made and I can tell that I'm really on the right track with my process. We'll see how long it takes to oxidize, but I'm planning on purging even more next time to be safe, so it's all good.

Here's the thing...I am planning to make a pumpkin beer at some point and I was going to add spices like I would a dry hop (dry spice if you will). I think it would be a serious problem trying to add spices while doing a continuous purge (spices in your face anyone? ). I was thinking of omitting the continuous purge while adding the spices, then sealing it up and purging with 16 rounds of 30 psi to get 0 ppm of oxygen. As a reminder, I am using a 6 gallon keg as a fermenter and my batches are 5.25-5.5 gallons (headspace would be 0.5-0.75 gallons). What is your opinion on this technique and do you think it would be a good technique for all beer styles?

 

[day_trippr]

Roughly what volume of spices is involved? I have been injecting "stuff" through the keg gas port using a big syringe and a bare gas QD, dissolved in a little water if necessary...

Cheers!

 

[sibelman]

Another approach to avoiding avoiding dust: stir the spices into a bit of vodka or Everclear, then pour that in.

Too, while dry hopped beers are very oxygen-sensitive, your pumpkin beer may better survive a bit of oxygen. Could be a RDWHAHB situation.

 

[doug293cz]

@doug293cz I just thought of something that you could probably help me with. I implemented the continuous purge with CO2 and purging after sealing. My beer was by far the best I've ever made and I can tell that I'm really on the right track with my process. We'll see how long it takes to oxidize, but I'm planning on purging even more next time to be safe, so it's all good.

Here's the thing...I am planning to make a pumpkin beer at some point and I was going to add spices like I would a dry hop (dry spice if you will). I think it would be a serious problem trying to add spices while doing a continuous purge (spices in your face anyone? ). I was thinking of omitting the continuous purge while adding the spices, then sealing it up and purging with 16 rounds of 30 psi to get 0 ppm of oxygen. As a reminder, I am using a 6 gallon keg as a fermenter and my batches are 5.25-5.5 gallons (headspace would be 0.5-0.75 gallons). What is your opinion on this technique and do you think it would be a good technique for all beer styles?

Purging with multiple cycles is a good method to get the O2 out of the headspace after opening for dry hopping or similar.

Brew on

 

[CyberFox]

Roughly what volume of spices is involved? I have been injecting "stuff" through the keg gas port using a big syringe and a bare gas QD, dissolved in a little water if necessary...

Cheers!

That's a good technique. I'm planning on at least a tablespoon of spice. I'd also like to dry hop my IPAs with ground up hops (you know what I'm talking about ), so I won't be able to continuously purge while adding those either.

Another approach to avoiding avoiding dust: stir the spices into a bit of vodka or Everclear, then pour that in.

Too, while dry hopped beers are very oxygen-sensitive, your pumpkin beer may better survive a bit of oxygen. Could be a RDWHAHB situation.

I did think of a tincture, but I also wanted the ability to add powdered ingredients, so I was looking for a different overall solution. It also crossed my mind that non-IPAs could likely survive some oxygen, but I want my beer as high quality as possible and I'm willing to use some extra CO2 to get it.

Purging with multiple cycles is a good method to get the O2 out of the headspace after opening for dry hopping or similar.

Brew on

Well, if it works, it works. This might be too nitpicky, but do you think that the 10 or so seconds of contact with oxygen would negatively affect the beer even if I purge the hell out of it after sealing?


Thanks guys!