newbie here with 1/2 batch & kegging questions

[jpakstis]

Hi everyone - I am a newbie to home brewing. I have brewed two batches so far, an imperial IPA and a kolsch and they seem to have come out well so far! I want to get into kegging so I've done lots of research but first, I think I would like to brew half-batches. We don't really drink a lot of beer in our house (my wife might have 1 bottle a week) and I haven't really had the opportunity to give out too many bottles to friends and neighbors. I don't want to drop all the way down to 1 gallon kits so the half-batches seem right in the sweet spot.

I would really like to brew some half-batches and so far I have been brewing from extracts. Are there kits out there for half-batches? Or do I basically take a full batch and halve it if I can? I know Northern Brewer sells 3 gallon BIAB kits but I'm not sure if I'm ready to leave extracts.

My second question is for kegging the half-batches. Which one is preferable, 2.5 gallon or 3 gallon kegs? And in terms of assembling the equipment, I assume the regulator is just a standard regulator, i.e. there is no 2.5g or 3.0g regulator? And same thing with the CO2 tank?

Thanks so much!

 

[m00ps]

I dont see the point in buying a bunch fo 3gal equipment. Id just go with the normal sized stuff for 5gal and use those. a 2.5gal batch in a 5gal primary fermentor is fine. and 2.5gal in a 5gal keg works jsut as well as a full sized batch as long as you purge the headspace. This way, you cna build up to 5gal if you makes some new friends by giving beer out.

For a CO2 tank, the bigger the better. It costs about teh same to fill a 10lb co2 tank and a 5lb and you dont need to fill it as often. win win

 

[douglasbarbin]

You should be fine splitting a 5-gallon kit in half, if that's what you want.

You could keg the half-batches in either, or even a 5-gallon keg. Just be sure to purge the keg's headspace of oxygen after you fill it with beer. Basically fill the key with CO2 and vent the oxygen out the top a few times.

The regulators are the same regardless of keg size. The CO2 tanks are sized according to how much CO2 they hold (i.e., 5 lb, 10 lb, etc.). My advice would be to buy the biggest one you can afford or have room for.

 

[chickypad]

Personally I like the smaller kegs, especially now that I'm doing mostly 2.5-3 gal batches. I've got some of the stackables which save room in the kegerator - I can fit 2 in place of one 5 gal. Certainly up to you of course, either will work. As mentioned you can scale any recipe to size, especially with extract it's pretty much straight division.

 

[FloppyKnockers]

If you're set on half batches and don't think you'll go back to full batches, here's my take.

Kegs: you can get 2.5 or 3 gallons. The amount of head-space is moot. You can even use full size kegs for half batches. There's no difference between drinking a keg to half empty and filling a keg half full (let's not get philosophical here) as long as you purge the oxygen.

half batch extract brewing: This is a tough one if you want to stay with kits. I have personally never done a kit. Always just find a recipe and go for it. For a half batch, you would obviously just halve the ingredients. Except for the yeast...I've never run into any problems using a full vial/pouch in a half batch.

Fermenting: I would not use a five gallon bucket for two and a half gallons of beer...too much head-space. The CO2 production is not where it needs to be in the beginning before it can replace the oxygen in there. Just my $.02 on that one. You can always go to the bakery section of your local grocery store and ask for empty frosting buckets. You may have to clean them yourself, but they are food grade, have a rubber seal, and are free.

CO2 tank and regulator: Fielder's choice here... a regulator is a regulator, 2.5#, 5#, 20#...they all hold CO2. The difference is the quantity and tank certification. Wait, what?!? What is tank certification?...well, I'm glad you asked. On the side of the tank is stamped a month and year. If you don't get the tank exchanged within 10 years of that date, you will likely have to pay a $35 cert fee (applies to me, here in Oregon anyway). I have a 5# tank in my kegerator. I can carb, pressurize, and dispense ~8 - 10 kegs with one tank. That should help with you math and planning.

 

[IslandLizard]

Along regular 5 and 10 gallon batches, I do a decent amount of 2.5-3.5 gallon ones too. I use smaller buckets (3.5-4 gallon) for those. For example the 4 gallon ones cake icing comes in (ask your bakery). They come with lids too so you can cut/drill a hole for an airlock grommet.

Now filling regular 5 gallon kegs with those 1/2 size batches is a bit of a trick, as you really want to pre-purge those so they are 100% filled with CO2 before racking your beer into them. That's way better and more economical than purging that large headspace after filling.

You can buy smaller kegs, 2, 2.5 and 3 gallon, but they run you way more money than 5 gal ones and there are very few to be found in the used market.

Now many beers get better with time, like many dark and high gravity beers, so brewing and storing 5 gallon only serves you longer and better for the same effort.

I would compound the recipes to the size you want, and buy the loose ingredients rather than kits. Check into All-Grain too, more flexibility.

 

[HomeDrewBrew]

Now filling regular 5 gallon kegs with those 1/2 size batches is a bit of a trick, as you really want to pre-purge those so they are 100% filled with CO2 before racking your beer into them. That's way better and more economical than purging that large headspace after filling.

So let the oxygen out before filling the keg makes sense but i dont understand why fill it with C02 before filling it with beer?
Wouldnt opening the lid of the keg let all the C02 out that u just put in?.
Sorry im a newbie also and trying to gather info.
Thanks

 

[jpakstis]

Thanks everyone for the responses. I have a BB kit with a 5 gallon carboy so I was thinking about primary in there. One of the main issues for getting the 2.5/3g kegs is space as well as amounts. I have a mini-fridge that I think will handle two 2.5 or 3g kegs in them nicely. I was thinking about having one on tap and lagering or cold-crashing another one when I get better at this.

 

[douglasbarbin]

Now filling regular 5 gallon kegs with those 1/2 size batches is a bit of a trick, as you really want to pre-purge those so they are 100% filled with CO2 before racking your beer into them. That's way better and more economical than purging that large headspace after filling.

That makes no sense. How is it more economical to completely fill the keg with CO2 as opposed to filling only the headspace with CO2? Totally unnecessary IMO.

 

[IslandLizard]

So let the oxygen out before filling the keg makes sense but i dont understand why fill it with C02 before filling it with beer?
Wouldnt opening the lid of the keg let all the C02 out that u just put in?.
Sorry im a newbie also and trying to gather info.
Thanks

I understand, it's quite easy, actually. I've developed the following method.

Partially filling a keg under CO2 while racking:

1. Fill the keg with Starsan to the top (~5.5 gallon), then purge it all out into a bucket with CO2, and blow out the last bits too that settle in the bottom. You now have a 100% CO2 filled keg.
   
   
2. Do NOT remove the lid, as that would allow air back in and mix quickly. Instead, when ready to rack, remove the gas post and dip tube and snake a 3-4' long 1/4" OD tubing down the threaded stub, it just fits. Make sure it ends up on the bottom, not curled up against the lid, to limit foaming. You may want to try and test this before purging. There should be a piece of tubing left sticking out the stub.
   
   
3. Open the PRV valve! You need to vent the CO2.
   
   
4. Start racking* and when the 3/8" racking hose is full with beer, connect it to the 1/4" tube sticking out the keg. Fill the keg this way. Keep the racking cane under the beer surface, and beware that no air gets sucked in, particularly at the end! Clamp off (!) when done, pull out the hose and remount the dip tube and post. If you want you can purge one more time, although it will make little difference. There cannot be much air gotten into the keg during this process.

*Although the racking part can be done by one person, it's easier to have another set of capable hands available.

 

[IslandLizard]

That makes no sense. How is it more economical to completely fill the keg with CO2 as opposed to filling only the headspace with CO2? Totally unnecessary IMO.

Main reason: it's 100% filled with CO2. Takes 5 gallons of gas.

I've not found a way to easily calculate how much CO2 is needed to purge a keg filled half with beer, half with air, to contain a gas mixture of 90% CO2 (and 10% air) at the end. I have the feeling it takes a lot more than 5 gallons. With less beer it's even more.

 

[douglasbarbin]

Main reason: it's 100% filled with CO2. Takes 5 gallons of gas.

I've not found a way to easily calculate how much CO2 is needed to purge a keg filled half with beer, half with air, to contain a gas mixture of 90% CO2 (and 10% air) at the end. I have the feeling it takes a lot more than 5 gallons. With less beer it's even more.

The beer pushes the air out when you rack it to the keg. So you only have 2.5 gallons of air to displace instead of 5.

 

[IslandLizard]

The beer pushes the air out when you rack it to the keg. So you only have 2.5 gallons of air to displace instead of 5.

That's what I said, half beer, half air. It takes multiple purges to remove 80-90% of that 2.5 gallons of air.

 

[AnOldUR]

It takes multiple purges to remove 80-90% of that 2.5 gallons of air.

It takes about five full purges at 30psi to get to (imo) "close enough" to pure CO2. If you're purging an almost full keg, that's not a lot. If you're purging a half filled keg you'll be blowing out a lot of gas.

The real advantage to IslandLizard's method is that his beer is not exposed to (and absorbing) oxygen during the transfer.

Charts thanks to doug293cz:

 

[douglasbarbin]

I am having some real difficulty understanding how the presence or absence of beer underneath the empty air affects the relative volume of CO2 needed to displace that air. If you have an empty keg, you have 5 gallons of air that need to be displaced. If you have a half-full keg, you have 2.5 gallons of air that need to be displaced. If you have 2 half-full kegs, you have 5 gallons of air that need to be displaced. And so on.

To phrase this another way, why would a half-full keg require multiple purges, but an empty keg only requires a single purge?

 

[douglasbarbin]

It takes about five full purges at 30psi to get to (imo) "close enough" to pure CO2. If you're purging an almost full keg, that's not a lot. If you're purging a half filled keg you'll be blowing out a lot of gas.

The real advantage to IslandLizard's method is that his beer is not exposed to (and absorbing) oxygen during the transfer.

Charts thanks to doug293cz:

This I understand, which is why I say if you're purging a totally empty keg, you're blowing out even more gas.

Regarding the absorption of oxygen during transfer, it seems like this would be very minimal and not worth the extra effort. It takes maybe 5 minutes for me to transfer 5 gallons to a keg, and air is ~21% oxygen. Surely that isn't enough to oxidize the beer, right?

 

[doug293cz]

Nice chart and table!

Note that 10 purges at 15 psi uses the same amount of CO2 as 5 purges at 30 psi, but gets you lower O2 content (0.088% of original O2 vs. 0.385%.) And 8 purges at 15 psi gives about the same results as 5 at 30 psi (0.360% vs 0.385%), while using 20% less CO2.

Since the gas mixing and math work on percentages, actual volume of headspace doesn't matter to the percentages. However, with larger headspace volume there is more total O2 for the same percentage O2.

Brew on

 

[AnOldUR]

This I understand, which is why I say if you're purging a totally empty keg, you're blowing out even more gas.

IslandLizard's method is purging 5 gallons once with 100% effeciency. Incrementally purging five or more times to get similar results, even though it's 2-1/2 gallons, is less efficient.

 

[douglasbarbin]

IslandLizard's method is purging 5 gallons once with 100% effeciency. Incrementally purging five or more times to get similar results, even though it's 2-1/2 gallons, is less efficient.

But WHY is it 100% efficient if there is no beer in the keg? That's what I'm asking. How does the addition of beer change that?

 

[AnOldUR]

When he pushes out the 5 gallons of sanitizer with CO2, 100% of the sanitizer is displaced by the CO2 and he can do it at a low pressure so the amount of CO2 used is small. If he then fills the keg half way with beer, he pushes out exactly half of that 5 gallon space worth of CO2. At that point there is no O2 in the headspace, so all he has to do is pressurize. No purging.

When you purge by pulling the pressure release multiple times, you're mixing gasses and never getting 100% displacement. Every time you release the pressure there's diminishing return. The last couple of purges, you're exhausting 2-1/2 gallons of mostly CO2, but still not achieving 100% CO2 in your headspace, and since it's under pressure the actual amount of loss is multiplied.

If you're filling half a keg and are concerned about using too much gas, IslandLizard's method is the way to go.

 

[douglasbarbin]

When he pushes out the 5 gallons of sanitizer with CO2, 100% of the sanitizer is displaced by the CO2 and he can do it at a low pressure so the amount of CO2 used is small. If he then fills the keg half way with beer, he pushes out exactly half of that 5 gallon space worth of CO2. At that point there is no O2 in the headspace, so all he has to do is pressurize. No purging.

When you purge by pulling the pressure release multiple times, you're mixing gasses and never getting 100% displacement. Every time you release the pressure there's diminishing return. The last couple of purges, you're exhausting 2-1/2 gallons of mostly CO2, but still not achieving 100% CO2 in your headspace, and since it's under pressure the actual amount of loss is multiplied.

If you're filling half a keg and are concerned about using too much gas, IslandLizard's method is the way to go.

Ahhh...so there is an assumption that the keg is filled with sanitizer and not actually an empty keg. I somehow missed the post where IslandLizard mentioned that. That makes a lot more sense. Thanks for clearing it up.

 

[IslandLizard]

Ahhh...so there is an assumption that the keg is filled with sanitizer and not actually an empty keg. I somehow missed the post where IslandLizard mentioned that. That makes a lot more sense. Thanks for clearing it up.

Yeah, you got it! Must have skipped step 1.

Partially filling a keg under CO2 while racking:

1. Fill the keg with Starsan to the top (~5.5 gallon), then purge it all out into a bucket with CO2, and blow out the last bits too that settle in the bottom. You now have a 100% CO2 filled keg.

 

[douglasbarbin]

Yeah, you got it! Must have skipped step 1.

I skipped the entire post, apparently. Everything you said makes a lot more sense now that I have gone back and read the relevant post.

 

[IslandLizard]

It takes about five full purges at 30psi to get to (imo) "close enough" to pure CO2. If you're purging an almost full keg, that's not a lot. If you're purging a half filled keg you'll be blowing out a lot of gas.

The real advantage to IslandLizard's method is that his beer is not exposed to (and absorbing) oxygen during the transfer.

Charts thanks to doug293cz:

Great charts, thank you!

Just for reference, the charts mention O2, but we're dealing with AIR, which contains only 21% O2. So the residual numbers should be divided by 5, to estimate the actual volume of O2 left over in our keg.

I wonder what would be an acceptable O2 percentage in the headspace or better yet, RATIO of O2 volume in headspace / beer volume underneath.
Why? Well, that last pint will oxidize much quicker than 2.5 gallons given the same amount of O2 present.

Now what they don't tell us yet, is how much CO2 is required to raise the pressure of a given volume of air (gas) to a certain psi. I've always had the feeling, when a keg is half full of beer, it takes more than 5 gallons of gas to purge that headspace 10x at 20 psi.

 

[doug293cz]

Great charts, thank you!

Just for reference, the charts mention O2, but we're dealing with AIR, which contains only 21% O2. So the residual numbers should be divided by 5, to estimate the actual volume of O2 left over in our keg.

I wonder what would be an acceptable O2 percentage in the headspace or better yet, RATIO of O2 volume in headspace / beer volume underneath.
Why? Well, that last pint will oxidize much quicker than 2.5 gallons given the same amount of O2 present.

Now what they don't tell us yet, is how much CO2 is required to raise the pressure of a given volume of air (gas) to a certain psi. I've always had the feeling, when a keg is half full of beer, it took more than 2.5 gallons of gas to purge that headspace 10x at 20 psi.

The chart and table are based on percentage of original air or O2 (doesn't matter), left after purge. For example, if you purge once with 14.7 psi, then you have 50% less air than you started with, and 50% less oxygen than you started with. If you want to know the percentage of O2 in the headspace after a purge, then you have to multiply by 0.21. So if you purge once with 14.7 psi then you have 0.5 * 0.21 = 0.105 => 10.5% O2 in the headspace, and the O2 partial pressure would be 14.7 * 0.105 = 1.54 psi. To know the total amount of O2 in the headspace, you need to know the headspace volume.

Edit: The volume of CO2 required for each purge cycle is:

Headspace_Volume * Regulator_Pressure / Atmospheric_Pressure​

Atmospheric pressure is 14.7 psi at sea level.

Edit2: If you want to convert the CO2 volume to lbs (or oz or grams) of CO2 then you need to do the calculation at standard atmospheric pressure (14.7 psi.)

Brew on

 

[IslandLizard]

The chart and table are based on percentage of original air or O2 (doesn't matter), left after purge. For example, if you purge once with 14.7 psi, then you have 50% less air than you started with, and 50% less oxygen than you started with. If you want to know the percentage of O2 in the headspace after a purge, then you have to multiply by 0.21. So if you purge once with 14.7 psi then you have 0.5 * 0.21 = 0.105 => 10.5% O2 in the headspace, and the O2 partial pressure would be 14.7 * 0.105 = 1.54 psi. To know the total amount of O2 in the headspace, you need to know the headspace volume.

Edit: The volume of CO2 required for each purge cycle is:

Headspace_Volume * Regulator_Pressure / Atmospheric_Pressure​

Atmospheric pressure is 14.7 psi at sea level.

Brew on

Hi, @doug293cz, a personal thank you for those fine charts and the detailed explanation. Very enlightening!

So along with your example, if the keg is half full (or half empty) there's 2.5 gal headspace * 14.7 psi (regulator pressure) / 14.7 psi (atm. pressure) = 2.5 gallons of CO2 used to half the amount of air (and thus half the O2). That makes a lot of sense, yes!

Twice the amount of gas in a volume => Twice the pressure and half the percentage.​

At that volume (2.5 gal) every purge at 14.7 psi uses 2.5 gallons of CO2.
4 complete purges will use 4 * 2.5 = 12.5 gallons of CO2 with a residual O2 level of 6% * 0.21 ~ 1.5% O2.

At 30 psi each purge takes 2.5 * 30 / 14.7 = 5.1 gallon of CO2.
2 purges @30 psi takes 2 x 5.1 = 10.2 gallons of CO2. Residual O2 level will be 10.8% * 0.21 ~ 2.3%

A third purge @30 psi will bring the O2 level down to 3.6 * 0.21 ~ 0.76% for a total cost of 15.3 gallons of CO2.
Or instead, a third purge only @15 psi will bring the O2 level to ~5.4 * 0.21 ~ 1.1% for a total cost of 10.8 + 2.5 = 13.3 gallons of CO2.

Compared to any of these methods, a complete pre-purge only takes 5 gallons of CO2 at near 0% O2, a savings of at least 50% of CO2.
Again, that's for a half filled 5 gallon keg.

In conclusion, the total pre-purging method is more economical for kegs that are filled less than about 3/4. Purging after filling is more economical for kegs that are filled 3/4 or more, for an acceptability level of residual O2 to be around 2% (2 purges at 30 psi).

 

[doug293cz]

Hi, @doug293cz, a personal thank you for those fine charts and the detailed explanation. Very enlightening!

So along with your example, if the keg is half full (or half empty) there's 2.5 gal headspace * 14.7 psi (regulator pressure) / 14.7 psi (atm. pressure) = 2.5 gallons of CO2 used to half the amount of air (and thus half the O2). That makes a lot of sense, yes!

Twice the amount of gas in a volume => Twice the pressure and half the percentage.​

So at that volume (2.5 gal) every purge at 14.7 psi uses 2.5 gallons of CO2. So 4 complete purges + a refill = 12.5 gallons of CO2 used with a residual O2 level of 6% * 0.21 ~ 1.5% O2.

You've got it. Except a 5 gal keg probably has a volume of more than 5 gal (I haven't actually measured). So if you had 2.5 gal of beer, you might have ~3 gal of headspace, and 4 purges + fill would use 15 gal of CO2.

Brew on

 

[IslandLizard]

You've got it. Except a 5 gal keg probably has a volume of more than 5 gal (I haven't actually measured). So if you had 2.5 gal of beer, you might have ~3 gal of headspace, and 4 purges + fill would use 15 gal of CO2.

Brew on

Wow, finding where that break even point lies is exactly what I've been wondering for a few years already. I had the gut feeling purging half empty kegs was a waste of gas, and no clue how much O2 would be left after each purge.

Sorry, I was editing the post while you posted your reply. A few things were changed, and I took out the refill, since that was incorrect. There is atmospheric level gas left after purging (pulling the ring), same as with the pre-purge method.

A 5 gallon keg has a bit over 5.5 gallon volume. I had to top up the 5 gallon of Starsan I had already poured in, to fill it to the bottom of the gas dip tube. The foam is deceptive of the actual fill level. So with that extra headspace the purge-after-filling becomes even bleaker. Maybe the break-even lies closer to 80% fill volume, around 4.5 gallons of beer...

 

[itsbarleytime]

I strongly recommend Brewing in a bag. All grain is so much better its a joke. In the beginning I didn't understand why it tasted like something was missing with extract so I brewed and brewed thinking my methods of brewing were wrong it was the extract. What ever equipment you use remember your beer comes first. Taste is first. All grain 1 gal will be easy and taste great. You will probably want to brew more because the taste will be impressive.

 

[jpakstis]

I strongly recommend Brewing in a bag. All grain is so much better its a joke. In the beginning I didn't understand why it tasted like something was missing with extract so I brewed and brewed thinking my methods of brewing were wrong it was the extract. What ever equipment you use remember your beer comes first. Taste is first. All grain 1 gal will be easy and taste great. You will probably want to brew more because the taste will be impressive.

I might try this. I'm going to the local home brew store to get the ingredients, but I'm thinking about this kegging system for the 2.5 gallon setup:

http://www.homebrewing.org/25-Gallo...ll-Lock-Keg-Rubber-HandleBottom-1_p_2890.html

Additionally, the instructions on the two brews I have had have had me brew 2.5 - 3 gallons of wort and then top it off to the 5 gallon mark with water to fill my fermenting bucket. Is there any issue with just fermenting the wort without the 2 - 2.5 gallon top off?