Half batch in 5g keg?

[rgreenberg2000]

So, I've got my first batch of Yooper's Oat Stout in the fermenter. Since I can't leave well enough alone, I want to try adding some coffee to this one. I'd like to split the batch (5g) in half, so I can have 2.5 gal of unadulterated YOS, and 2.5 gal with added coffee to compare.

Here's my question. I only have two 3g kegs, and one of them is currently serving my Cigar City Maduro. So, if I split the batch, I'll need to put half in a 5 gal keg. Just curious if I'm setting myself up for any unforeseen issues with the extra head space? Spend extra time purging since there will be more O2? Longer time to carb?

As I type, I'm thinking maybe I can rack onto the coffee in the 3 gal keg, then do a closed transfer of that to the 5 gal keg to keep the O2 exposure low.....

I need more coffee.... See where this started?

Rich

 

[m00ps]

no issues so long as you are able to purge it. No different than if you had a full 5gal keg and drank half of it. The 2.5gal left isnt gonna spoil...

 

[CamG]

I am in a similar situation except want to put 1g in a 5g keg so I can't wait to hear the advice. My thoughts on it were that besides using extra Co2 to purge there should not be any other negative effects.

 

[BeardedBrews]

I have been seeing more recommendations to fill the empty keg with liquid (star-san / water) and then use CO2 to push the liquid out.

Since the CO2 will mix with the gasses in the headspace, thinking of it as a "purge" isn't quite right. It's more like you're diluting the air in the keg with CO2 each time you vent the top. At some point you can dilute it down to where there won't be problems, but you would use way more CO2 than simply displacing all of the air in the tank with liquid, and then pushing a single volume of CO2 in to replace it.

The added benefit, is that if you use (and save) Star-San, you will have a nice and sanitzed dip tube.

 

[rgreenberg2000]

Thanks for the quick feedback, folks! I like the idea of doing a Star San transfer with the 5 gal to reduce the amount of oxygen that's there to be purged/displaced. I usually have one of my kegs somewhat full of Star San all the time just to have it on hand when I need it, so this will be easy. Need to sanitize the kegs before racking anyway.

Ok, got a plan for splitting the batch, now off to finish my research on adding coffee to the brew. I think for this one, I'll be doing a cold press brew of my current house coffee (Peet's Major Dickason.)

Thanks again!

Rich

 

[HausBrauerei_Harvey]

I did this a few months back for the first time. I was able to attach a bit of sanitized tubing around the gas-in post which I cut to end just an inch or so above my beer. Worked great, no oxidation issues noted on a light lager I served. I did the tube trick because I was worried about not getting good mixing of the CO2 coming in when purging, it may not have been necessary but it made me feel better.

 

[IslandLizard]

I have been seeing more recommendations to fill the empty keg with liquid (star-san / water) and then use CO2 to push the liquid out.

Since the CO2 will mix with the gasses in the headspace, thinking of it as a "purge" isn't quite right. It's more like you're diluting the air in the keg with CO2 each time you vent the top. At some point you can dilute it down to where there won't be problems, but you would use way more CO2 than simply displacing all of the air in the tank with liquid, and then pushing a single volume of CO2 in to replace it.

The added benefit, is that if you use (and save) Star-San, you will have a nice and sanitzed dip tube.

^ This!

Fill that keg 100% with Starsan, so headspace is minimal. You could even overflow it if you're very concerned (IPAs).

You'd use 5.5 gallons of CO2 to purge and you'll end up with a keg that has almost 100% CO2 in it, and a little air (from under the lid).

If you would purge the headspace of a keg that was only partially filled, you'd use way, way more CO2 and it would never be anywhere close to a 100% purge. The break even point of using 5.5 gallons of CO2 (at 2% residual air) lies already around only 4 gallons of fill volume! Getting exponentially worse with lower fills.

When filling a 100% pre-purged keg, fill through the liquid out post, and open the PRV. Do not remove the lid or your pre-purge efforts were futile!

 

[rgreenberg2000]

When filling a 100% pre-purged keg, fill through the liquid out post, and open the PRV. Do not remove the lid or your pre-purge efforts were were futile!

Yep, this part was my plan all along! This brew will also very likely be the first one where I do a pressurized transfer from my Chronical to the keg, so I had already planned on racking in via the "outlet" on the keg to reduce splashing, etc.

I'll make sure that I purge both kegs first by filling with Star San, then pushing that out with CO2.

Thanks!

R

 

[IslandLizard]

Yep, this part was my plan all along! This brew will also very likely be the first one where I do a pressurized transfer from my Chronical to the keg, so I had already planned on racking in via the "outlet" on the keg to reduce splashing, etc.

I'll make sure that I purge both kegs first by filling with Star San, then pushing that out with CO2.

Thanks!

R

Perfect! Great to be able to transfer under pressure too.

You need to go over every detail to eliminate any air from being transferred accidentally.

After purging the keg, I pressurize it a bit, so I can blow out the residual Starsan that has collected over the next 10-15 minutes while I get everything else ready. While flowing CO2 at low pressure I mount my QD with a piece of hose on it, so that's purged too. Then start racking to fill the racking hose all the way with beer. Clamp off, and attach to the hose stub on the QD. Open the PRV and let her rip. :rockin:

Just be careful not to overfill, if you don't want that, although you could. Once beer comes out the PRV or open gas QD, you know there's no headspace left, so you're 100% purged again. Push out 12-16oz to get some headspace and a taster, then pressurize for carbonation.

 

[Jim311]

I'm not sure I'd waste 5 gallons of Star San to save 5 gallons of CO2 personally. I guess if you save the Star San every time it's not wasted, but I fill kegs often enough to where I'd be sitting on 20 gallons of Star San way before it went bad. I think there's also some bad math here. If you fill the keg with 5 gallons of liquid, and then DISPENSE all of it with CO2, you've still used 5 gallons of CO2 because the CO2 is displacing the liquid. As far as purging, I guess mathematically you'll never get to 100% CO2 in the keg, but with a quick purge or two you're going to dilute the air in the keg so much that it is statistically irrelevant. I don't think you really need to fill the whole keg to 40 PSI and then blow it off half a dozen times, that's a waste. You don't even have to pressurize it that much to displace the air inside. Anyway, I don't really worry too much about it. I hook up my CO2 to my liquid out post, burp it a few times, transfer in my beer, and call it a day. I'm still way way better off than I was bottling and I don't taste any stale oxidation. I think with my IPAs I'm going to start using the "set it and forget it" method so I don't have to blow off the keg during the kegging process and waste all that delicious hop aroma I paid so much money for.

 

[rgreenberg2000]

Jim311, this hobby wouldn't be any fun if we didn't overthink every single facet, right?!?!? In reality, I'm a lot less strict about most of this than some, but if I can come up with a low stress, reasonable set of steps that preserves the work that went into the batch, then that works for me.

Oh, and I typically have about four gallons of Star San that I move around from keg to keg or vessel to vessel depending on when/where I need it. I'm with you, I don't want to waste it, and don't need 20 gallons of it either!

R

 

[IslandLizard]

[...] I think there's also some bad math here. If you fill the keg with 5 gallons of liquid, and then DISPENSE all of it with CO2, you've still used 5 gallons of CO2 because the CO2 is displacing the liquid. As far as purging, I guess mathematically you'll never get to 100% CO2 in the keg, but with a quick purge or two you're going to dilute the air in the keg so much that it is statistically irrelevant. I don't think you really need to fill the whole keg to 40 PSI and then blow it off half a dozen times, that's a waste. You don't even have to pressurize it that much to displace the air inside. Anyway, I don't really worry too much about it. I hook up my CO2 to my liquid out post, burp it a few times, transfer in my beer, and call it a day. I'm still way way better off than I was bottling and I don't taste any stale oxidation. I think with my IPAs I'm going to start using the "set it and forget it" method so I don't have to blow off the keg during the kegging process and waste all that delicious hop aroma I paid so much money for.

Take a gander at these 2 threads (among many others on the topic) and see if you can still agree with what you just wrote. Pay special attention to the graphs posted by @doug293cz:

Newbie here with 1/2 batch & kegging questions

Purging Kegs

Especially for IPAs you want to fill a 100% pre-purged keg since this prevents BOTH oxidation AND the need to purge the headspace (and thus aroma) after filling.

 

[Jim311]

Take a gander at these 2 threads (among many others on the topic) and see if you can still agree with what you just wrote. Pay special attention to the graphs posted by @doug293cz:

Newbie here with 1/2 batch & kegging questions

Purging Kegs

Especially for IPAs you want to fill a 100% pre-purged keg since this prevents BOTH oxidation AND the need to purge the headspace (and thus aroma) after filling.

One thing about that chart is that it doesn't compare low pressure purges. I notice there's not a huge difference in purging with 10 PSI versus say 30. But what about below 10PSI? What about 5? 2? That information is missing. Also, where did this information come from? I don't purge at high PSI. Anyway, even after seeing the charts I still don't really change my mind and here's why.

Firstly, CO2 is cheap compared to Star San. This assumes the Star San eventually goes to waste, but maybe you can run through 10 gallons of Star San before it's time for the next brew. Or maybe you reuse the Star San for the next 10 batches and don't care. But I don't. I probably brew 5-10 gallons each month or maybe every other month so I'd end up with tons of Star San I'd have to store.

Secondly, lets talk about just how much CO2 we are using here. Let's assume you can get a 20LB CO2 cylinder filled for 25 dollars just for easy math. To fill 5 gallons of head space we need .015 pound of CO2. I used this site to figure this out:

http://www.airproducts.com/products...ht-and-volume-equivalents/carbon-dioxide.aspx

We can do this approximately 1333.33 times before our CO2 tank runs out. If we paid 25 bucks for this CO2, this means each purge costs us .01875 dollars. Unless my math is wrong (please feel free to correct me) each purge costs me LESS than two cents. So I'm going to go ahead and go with the option that's easier and costs virtually nothing, and not have to pay for whatever 5 gallons of Star San costs, and not have to store said 5 gallons of Star San until the next brew day or whatever. But that's just like, my opinion, man. I don't sweat the petty things, and 20 cents ain't that important to me. I'm also not going to purge 7 times. Maybe 3 times at the most. Is that wrong? Maybe, but it still makes good beer. Brew on.

 

[doug293cz]

One thing about that chart is that it doesn't compare low pressure purges. I notice there's not a huge difference in purging with 10 PSI versus say 30. But what about below 10PSI? What about 5? 2? That information is missing. Also, where did this information come from? I don't purge at high PSI. Anyway, even after seeing the charts I still don't really change my mind and here's why.

...

If you think there isn't a huge difference between purging at 10 psi and 30 psi, you don't understand the chart. It takes 19 purge cycles at 10 psi to get to the same residual O2 level that you get with 9 cycles at 30 psi. That's a big difference in time spent, although the 19 purges at 10 psi will use slightly less CO2 (but as you said, CO2 is cheap.) You should be able to tell from the data present in the original chart & table that the lower the purge pressure, the more purge cycles it takes to get to the same level of residual O2. That trend doesn't suddenly change when you go below 10 psi. Just for you, I updated the chart and table for lower psi's. It's clear that low pressure purging is not practical if you want to get to less than 0.1 ppm (or even 1 ppm) O2.





The calculations are based on the ideal gas law, simple dilution math, and the assumption that the purge CO2 mixes completely with the gas in the keg headspace.

Brew on

 

[BeardedBrews]

The calculations are based on the ideal gas law, simple dilution math, and the assumption that the purge CO2 mixes completely with the gas in the keg headspace.

Brew on

Hey Doug, is it possible to relate a continual vent for X seconds to a number of purges?

 

[mongoose33]

I'm missing how people would have "tons of Star-San to store" in doing a Star-San purge.

What I see is this:

1. Mix up 5 gallons of Star-San solution, in keg or bucket; pour in keg.

2. Push out Star-San via CO2 purge; collect Star-San in a bucket or another keg.

3. Use that Star-San next time.

All you have to store is 5-gallons of Star San. I keep using mine as long as it suds up and remains clear.

In fact, if you had a spare keg, couldn't you keep that spare filled with Star-San (after cleaning it) so that it would be ready to be purged and filled each time, collecting the Star-San in the next keg in the line?

 

[Jim311]

If you think there isn't a huge difference between purging at 10 psi and 30 psi, you don't understand the chart. It takes 19 purge cycles at 10 psi to get to the same residual O2 level that you get with 9 cycles at 30 psi. That's a big difference in time spent, although the 19 purges at 10 psi will use slightly less CO2 (but as you said, CO2 is cheap.) You should be able to tell from the data present in the original chart & table that the lower the purge pressure, the more purge cycles it takes to get to the same level of residual O2. That trend doesn't suddenly change when you go below 10 psi. Just for you, I updated the chart and table for lower psi's. It's clear that low pressure purging is not practical if you want to get to less than 0.1 ppm (or even 1 ppm) O2.

View attachment 344966

View attachment 344967

The calculations are based on the ideal gas law, simple dilution math, and the assumption that the purge CO2 mixes completely with the gas in the keg headspace.

Brew on

Thanks for posting more info. I do not at all intend to get down to 1 part per MILLION of oxygen. I think that's splitting hairs into a million parts. I think there will be no detectable difference on a homebrew level between a beer purged a few times and one purged 30 times to 1PPM. I think it's a colossal waste of gas. If you purged to even 1000PPM you've still got 100 times less O2 you had before! Remember when you'd transfer to a bottling bucket, where it would sit for half an hour completely exposed to oxgen while you bottled up all your beers? Did those beers suck? Mine didn't. I guess the gist of it is that if you're the type of guy who likes to crunch numbers and split hairs then you either need to do the Star-San method, or transfer it into a keg purged as many times as you feel necessary. Hell sometimes I don't even purge, I just transfer straight into the keg through the lid opening, and then gas her up and burp it a few times. I think some people vastly overcomplicate brewing, but I'm all about low effort unless it makes bad beer. After reading a ton of Brulosophy experiments, I'm leaning towards low effort because it's more fun to me. There's no "wrong" way to do it. These debates are fun, and it's good that the information is out there for people to decide for themselves, and that we can engage in them in a civil manner without people getting their feelings hurt. Have fun, I say!

 

[doug293cz]

Thanks for posting more info. I do not at all intend to get down to 1 part per MILLION of oxygen. I think that's splitting hairs into a million parts. I think there will be no detectable difference on a homebrew level between a beer purged a few times and one purged 30 times to 1PPM. I think it's a colossal waste of gas. If you purged to even 1000PPM you've still got 100 times less O2 you had before! Remember when you'd transfer to a bottling bucket, where it would sit for half an hour completely exposed to oxgen while you bottled up all your beers? Did those beers suck? Mine didn't. I guess the gist of it is that if you're the type of guy who likes to crunch numbers and split hairs then you either need to do the Star-San method, or transfer it into a keg purged as many times as you feel necessary. Hell sometimes I don't even purge, I just transfer straight into the keg through the lid opening, and then gas her up and burp it a few times. I think some people vastly overcomplicate brewing, but I'm all about low effort unless it makes bad beer. After reading a ton of Brulosophy experiments, I'm leaning towards low effort because it's more fun to me. There's no "wrong" way to do it. These debates are fun, and it's good that the information is out there for people to decide for themselves, and that we can engage in them in a civil manner without people getting their feelings hurt. Have fun, I say!

I too was in the camp thinking there was no need to get down to less than 1 ppm to avoid oxidation tastes in the beer. That was until I started doing more reading about quantitative measurements of total packaged oxygen (TPO) effects. Check out this presentation on commercial beer packaging O2 levels. In particular pay attention to page 21, where they found that taste changes in an IPA could be detected after 3 weeks with only 0.15 ppm TPO. If you keep your beer cold, it will take longer for the oxidation effects to show up, but they will happen eventually. Your taste threshold for oxidation products may also be higher than the professional tasters.

I agree that each brewer needs to decide how much effort they wish to expend on each phase of brewing. I geek out on the math and science, and create charts and such, so that other homebrewers can have solid information to use when deciding how to conduct their processes. Informed decisions are better then wild ass guesses. For the brewer who wishes to keep their IPA's great by keeping TPO less than 0.1 ppm, they need to know that 5 purges at 10 psi isn't going to do it. For the brewer who is happy with their beer and only does 3 purges, no problem. But, the one who says "my beer tastes like cardboard" needs solid advice on what they can do to fix the problem, and the advice should be based on solid fundamentals, not old wives tales.

Brew on

 

[doug293cz]

Hey Doug, is it possible to relate a continual vent for X seconds to a number of purges?

I'll have to think about that. As a minimum, you would need to know the flow rate of the CO2 into the headspace, and the actual headspace volume, in order to be able to control such a process and have a quantifiable result.

Brew on

 

[Jim311]

I too was in the camp thinking there was no need to get down to less than 1 ppm to avoid oxidation tastes in the beer. That was until I started doing more reading about quantitative measurements of total packaged oxygen (TPO) effects. Check out this presentation on commercial beer packaging O2 levels. In particular pay attention to page 21, where they found that taste changes in an IPA could be detected after 3 weeks with only 0.15 ppm TPO. If you keep your beer cold, it will take longer for the oxidation effects to show up, but they will happen eventually. Your taste threshold for oxidation products may also be higher than the professional tasters.

I agree that each brewer needs to decide how much effort they wish to expend on each phase of brewing. I geek out on the math and science, and create charts and such, so that other homebrewers can have solid information to use when deciding how to conduct their processes. Informed decisions are better then wild ass guesses. For the brewer who wishes to keep their IPA's great by keeping TPO less than 0.1 ppm, they need to know that 5 purges at 10 psi isn't going to do it. For the brewer who is happy with their beer and only does 3 purges, no problem. But, the one who says "my beer tastes like cardboard" needs solid advice on what they can do to fix the problem, and the advice should be based on solid fundamentals, not old wives tales.

Brew on

Rock on, I'm all about solid science and facts. But if it takes 4 months under refrigeration for off flavors to show up, I'll be fine, because a keg of delicious IPA is gonna disappear way faster than that around my house

Also another thing I thought of, is that the beer in that keg is only even exposed to the residual oxygen in the keg for a few minutes while the beer transfers from the carboy. Once the keg is full, there is WAY less head space and one must assume even less oxygen once I give it a few burps again. Less volume should be easier to purge, right?

 

[doug293cz]

Rock on, I'm all about solid science and facts. But if it takes 4 months under refrigeration for off flavors to show up, I'll be fine, because a keg of delicious IPA is gonna disappear way faster than that around my house

Also another thing I thought of, is that the beer in that keg is only even exposed to the residual oxygen in the keg for a few minutes while the beer transfers from the carboy. Once the keg is full, there is WAY less head space and one must assume even less oxygen once I give it a few burps again. Less volume should be easier to purge, right?

At the same O2 concentration, lower headspace will contribute less to TPO than more headspace. TPO is calculated as:

(Headspace_Vol * Headspace_O2_ppm + Beer_Vol * Dissolved_O2_ppm) / (Headspace_Vol + Beer_Vol)​

Edit: The rates of typical organic chemical reactions double (half) for each 10˚C increase (decrease) in temperature. So, if it takes 3 weeks at 20˚C (68˚F) for beer to start noticeably oxidizing, then at 3˚C (~33˚F) it would take:

3 wks * 2 ^ ((20˚ -3&#730/10&#730 = ~9.7 wks​

Brew on