15.5gallon keg for 5 gallon batch. Too much Headspace?

Well the title pretty much says it. I have had a couple batches of cider turn on me with infection in my fermentation buckets and I'm trying to get away from using plastic as I don't like the ambiguity of the sanitation with them. I have a 15.5 gallon Sanke with the spear taken and is all clean and ready to go.

Now I know that they can easily be used as fermenters but it appears that most everyone is using them for 10 gallon batches or more. I realize this is a little overkill for a 5 gallon batch but I don't have many options. I also realize that theoretically during the primary I should be getting enough CO2 production to purge the O2. However, I'm simply looking to see if anyone has any REAL WORLD experience using them for such a small batch. Anyone out there care to share your experience where the batch occupied about 1/3 the fermenter volume?

P.S. I realize a pony keg (7.5gallons) would be ideal but I have to use what I have around me for now.

If you purge the headspace prior to filling I see no problem. Actually, so much CO2 is produced there shouldn't be a problem just filling with 5 and letting it rip; however, I would only do so experimentally. If you have the means, which I assume you do having the keg in the first place, purge and ferment. I do a pressure fermentation in a closed system, so I can talk about just how much is produced. I have carbonated beer at the end of my primary fermentation and gas is always exiting my Sanke. Purge to be safe and let it rock and roll.

How do you know how long to purge it for? Is there a rule a thumb or do you just turn the CO2 on for 30 seconds or so? Do you do this slowly or does it not matter?

Sorry about all the dumb questions but I have most of a kegging system but have not used it yet so I'm new to working with CO2.

A purge is just filling to a slight pressure and then exiting from the top of the vessel in a closed setup like a sealed keg. If you are in a open vessel like a carboy or an open keg, just run it slow until it burns your nose at the top opening. Then you know you have that "blanket" of CO2 on top of your beer and most/all of the O2 out.

Ahhhhh..... the old burning of the nose trick. See I knew you would have a rule of thumb for me.

Do you really need to fill the whole thing up with CO2?

If you put a blanket down a couple of inches thick I imagine it would insulate the beer from oxygen. Then as it ferments the blanket will get thicker and then eventually push the atmospheric air out.

The only problem I see is the momentum of the co2 bubbles may disrupt the blanket and cause it to mix with air but that is only speculation.

Is making a 10 gallon batch of cider out of the question?

Or are you planning on fermenting your beer in it as well.

CodeRage said:

Do you really need to fill the whole thing up with CO2?

If you put a blanket down a couple of inches thick I imagine it would insulate the beer from oxygen. Then as it ferments the blanket will get thicker and then eventually push the atmospheric air out.

The only problem I see is the momentum of the co2 bubbles may disrupt the blanket and cause it to mix with air but that is only speculation.

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I really don't think I need to completely fill it with CO2 for the exact reason you stated. However, I'm not used to purging with CO2 so I might fill it completely just to learn how to work with it. But yeah I agree with your point.

IXVolt said:

Is making a 10 gallon batch of cider out of the question?

Or are you planning on fermenting your beer in it as well.

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I will be fermenting a batch of beer in it on Friday and then transferring to a corny after primary starts to wind down. I could ferment some cider in it but I'm planning on doing two different batches of cider in cornies as I won't have a krausen with them.

I'm kind of excited to ferment in stainless. I'm thinking I might boil my sparge water in the keg/fermenter. Then I can hit it with some starsan that will be sitting around anyway. I'm starting to understand why some people are so adamant about stainless....... It's just so versatile and indestructible.

You guys are right about the blanket and not filling the keg completely with CO2, but it is cheap and why not? In a fermenter you just need the blanket started if you are worried, but in a kegging situation with a sealed keg you do need to purge out all O2. Just thought I should clarify that, as if you have any O2 left in a sealed up keg it will oxidize the beer when you try to move the keg around.

In actuality, you probably don't need to add any CO2 to a fermenter. Fermentation produces a lot of CO2, way more than most people understand is there.

In my setup, and the way I ferment, I have 3-3.5 gallons of headspace for a 12-12.5 gallon batch and I have anywhere from 5-10 psi in the first day of fermentation farting out of my spunding valve constantly until fermentation is almost done. I have so much produced, that I seal it up tight a couple of points shy of finish and still have plenty to carbonate my beer.

I would assume, notice I said assume because I have never done a small batch in a keg, that with 10-10.5 gallons of headspace I would still be fine. My motto, better to be safe than sorry, but hey... I'm an Eagle Scout, lol.

WortMonger said:

You guys are right about the blanket and not filling the keg completely with CO2, but it is cheap and why not? In a fermenter you just need the blanket started if you are worried, but in a kegging situation with a sealed keg you do need to purge out all O2. Just thought I should clarify that, as if you have any O2 left in a sealed up keg it will oxidize the beer when you try to move the keg around.

In actuality, you probably don't need to add any CO2 to a fermenter. Fermentation produces a lot of CO2, way more than most people understand is there.

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Good to know. Yeah Co2 is cheap but I have to take a lunch break and drop my tank off across town, then break again the next day to pick it up. It's more of a logistics thing for me

I will be fermenting with an airlock and not under a closed system. This time I'll have a rubber stopper in the Sanke opening but next time perhaps I can use my Sanke tap and modify the Spear. I'm planning on putting a full CO2 blanket down until it burns my nose, as you put it. This will ensure nothing oxidizes and it will allow me to figure out how long it takes to fill the keg completely. The next time I do it perhaps I can cut that time in half.

I am doing this primarily because I see so many compromises with glass carboys (dangerous), plastic buckets (scratch) and Better Bottles (scratch). Just my opinion so don't take offense. I want the piece of mind that comes with stainless and the fact that you can throw a nuclear bomb in it to sanitize if you want. The funny thing is I never understood why people liked stainless so much before but the sickness has taken over.

Get up, come on get down with the sickness! As Richard Cheese puts it.

Maybe its my training, but you want to aerate your wort before pitching? Aerating at 212f no. but at pitching temp of 70c yeah you want to aerate your wort.

Noone said the wort would not be aerated. We are talking about headspace in the fermenter. You are right about wort needing to be aerated though, and about it being cold before doing so. This is why I said there should be no problem with letting nature take its course and just fill the fermenter and let it rip as normal. Purging the airsape would have no effect other than not allowing oxygen on the very top of the wort, which really shouldn't be a problem. I only suggest purging if you are really worried, but I find worrying unfounded in that fermentation should start quickly and cut off any O2 on the surface anyway.

agreed. Once co2 is being formed it will sink to the surface lvl of the wort. just chuck your wort in there and pitch and normal. just may take longer to fill the head space with co2...

I concur Sir! But... it will hurt nothing to purge if you want to.

I did a 5.5g batch in a 15g minibrew fermenter that I used to have and the batch turned out just fine. It was an Oatmeal Stout. That was the one and only time I used it because it was a PITA to get the wort into the fermenter.

How was it hard to get the beer in the fermenter? It looks like the whole lid comes off. Am I wrong? I have never seen one and am curious.

lifting a sankey keggle with 6.0 gal of wort into the minibrew conical was a PITA IMO. I do not have pumps or a way to elevate the keggle about the fermenter.

zman said:

I did a 5.5g batch in a 15g minibrew fermenter that I used to have and the batch turned out just fine. It was an Oatmeal Stout. That was the one and only time I used it because it was a PITA to get the wort into the fermenter.

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This is great news. I'm glad someone has tried something similar and it worked well. I'll update this thread when I'm done to let you all know how it worked out (Brewing Monday). The beer will need ~5 months to age so I won't be able to say too much but I'll talk about the process and about how initial fermentation went at least.

Yeah the wort will be areated (after chill) like I always do. I typically dump it back and forth from my boil kettle (turkey fryer pot) to a bucket fermenter. Can't really take this approach with a Sanke so I'll use my wort areator tip on the auto siphon and then shake the crap out of it in the 15.5 sanke.

I agree with all that the CO2 purging isn't necessary and I might not even do it. However, I would like the experience working with my CO2 and regulator and like already mentioned it won't hurt anything.

Any other experience would be great.

can i keg 12 gal in a 17 gal keg

zman said:

lifting a sankey keggle with 6.0 gal of wort into the minibrew conical was a PITA IMO. I do not have pumps or a way to elevate the keggle about the fermenter.

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Sanitized 5 gal bucket.

vertilizer said:

can i keg 12 gal in a 17 gal keg

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Sure. I do something similar all the time. You just have to purge more head space with CO2.