Carboy Capacity

I know that this has been discussed at length (I've read 10+ threads here after a search), but I still can't determine what's right for my situation, so I'm just going to ask directly.

I'm an all-grain brewer. I usually stick to smaller beers, since things like a quality Ordinary Bitter are so much more difficult to come by commercially (I can buy a excellent hoppy IPA just about anywhere). I have a 5G Igloo Cooler Mash Tun and 2 5G glass carboys, although I've never bothered to rack to secondary with my brews because I don't generally dry hop or add any ingredients (although a coffee porter is on my list soon). Works fine for me.

First question: Both my carboys were hand-me-downs. I was told they were 5G, and my 5G batched come up to the last "line" in the glass "grid" before the neck starts to curve heavily. I assume that the 5G measurement includes that amount of head space rather than literally taking it to the top of the neck. However, if I am wrong and I actually have 6G carboys, someone please let me know

Back to the questions: a friend of mine wants a primer on brewing in general and all-grain in particular, and he desperately wants to make a Pliny the Elder clone with me. I knew that I'd have to upgrade to a 10G mash tun, which I had planned on doing eventually so that I could use my 5G as a HLT with spigot, which is going to make things a lot easier for me (I usually fly sparge). So I did so.

However, now I'm realizing that my carboys are probably not big enough to contain a 5G batch of Pliny with all the dry hops and krausen. I recently made a 5% ABV Fat Tire clone and got a GREAT krausen off the Belgian yeast, but I would consider it the max my carboy could handle. I was hoping for some definitive knowledge before going out and spending money on a new glass carboy (and I prefer carboys to buckets and glass to plastic; I know some people with disagree but that's my preference).

Another thought that I had that would make for an interesting experiment: what if I racked HALF of it to the second carboy and split the dry hops. Half would be dry hopping in primary with the yeast cake. I know there are proponents for both techniques but that it doesn't really seem to make a fundamental difference outside of considerations like ease of cleanup and the effort and risks associated with racking.

I know that batches can be scaled to whatever size you want, so this makes inherent sense, but does letting 2.5G sit on what was a yeast cake from a 5G batch make any difference? Assuming it's healthy but dormant yeast I would say probably not, and it won't sit on there for more than 6 weeks.

On the other hand my wife will NOT be happy with having TWO fermentors sitting out in the kitchen for 3 weeks (we don't have a big house) and I don't mind investing in new equipment when it's necessary. I also want this batch to come out as good as possible for my friend's sake, so am less amendable to risking a batch as a test than I normally am. Plus, it's a particularly expensive batch for me (high grain bill, double hops, double yeast, dry hops, etc.; my next "level up" in brewing is to make yeast starters and then get a stir plate, but I haven't made that leap yet).

So,

1. Am I correct that I have 5G fermentors?
2. If so, is it 100% inadvisable to attempt this beer using two 5G carboys (one for primary and racked to the other for secondary for the dry hopping)?
3. If so, should I jump up to a 6G carboy or try splitting the batch?
4. Any other ideas?

Thanks!

#4 - go for a 6.5 gallon carboy if you decided to go larger in size. After than I'm out of advice. Wait no, just reread your post

I would NOT split the batch post ferment for the dry hopping and leave a 2.5 gallon headspace in each. That is asking for oxyidation issues/problems, unless you can purge with co2.

I would probably look for a 6.5 gallon and expect a blow off tube as needed. Also I'd then rack to a 5 galon 2ndary all of it for the dryhop, or put it in primary. either way, very little O2 contamination. The only splitting(#2) I would do would be to split the primary ferment and combine at the dry hopping.

Sounds like 5 gallon carboys to me.

I don't ferment anything in my 5 gallon carboy - just too much blowoff and such. With the dry hopping you'll need, a single 5 gallon is just not going to work unless you scale things down or split the batch, and I don't think you want that much headspace for dry hopping.

I'd personally buy a 6.5 gallon carboy for use as your new primary.

Thanks for the advice. I didn't consider potential oxidation. This is exactly the reason I decided to ask the boards

Considering that I will be giving half of the batch to my friend I definitely want to keep it at scale. My Fat Tire Clone clearly maxed out my current capacity for a 5G batch. It sounds like I will go for a 6.5G carboy to enable bigger beers in the future. At least I never paid for the ones I already have. I learned a similar lesson with the 5G vs. 10G igloo coolers, and at least I am also happy to reuse the 5G as a HLT.

Important lesson to new brewers: having a "5 gallon" carboy and a "5 gallon" Mash Tun does not mean that you can brew 5 gallons worth of any style beer. On both you will max out at a "medium" beer (<4-5% ABV) (or have to scale down, which is annoying).

Then I will probably rack to my current 5G carboy to dry hop.

Thanks!

Another way of determining your carboy size is by actually pouring measured amounts of liquid and marking off half-gallon marks as you go. These marks will come in handy.

In my opinion, oxidation issues aren't that prevalent in primary fermentors, since the beer is going to be producing a lot of CO2 and will be pushing out the oxygen on its own. Racking to a secondary fermentor when the primary fermentation is already done is when you should be more concerned about oxygen headspace. I usually have a significant amount of headspace in my 6.5 gallon primary fermentors and none of my beers have ever developed cardboardy flavors.

BrewLocal365 said:

On the other hand my wife will NOT be happy with having TWO fermentors sitting out in the kitchen for 3 weeks (we don't have a big house)

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Be sure to keep those fermentors covered up. UV light will skunk your beer while it's fermenting. You don't want that.

BrewLocal365 said:

At least I never paid for the ones I already have.

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They have this place you should check out... craigslist... [/sarc]... But seriously, I found 5 carboys on craigslist once, I got them for gas (it was about 100 mils round trip) and $30 or so I think... I recall selling on of them, and I still have 2 5 gal, 1 6 or 6.5 gal and a 2.8 gal carboy plus 2 cases of wine bottles. A very good hall for only 30 or $40.

Anyhow, check craigslist for peopel bailing on brewing and buy their stuff.

LandoLincoln (awesome handle): they are currently in use so I couldn't do the measured pour. But you made me realize that my plan to split the batch wouldn't work anyway because if I use them both at once I have nothing to rack to! I always cover up with a towel or blanket, both for UV protection and temperature "control".

ACbrewer: Craigslist was going to be my first stop. Thanks!

I primary in 6.5 gal carboys. Anything higher than 1.050 gets a blowoff tube. From there, I'll rack to a 5 gal for dry hopping.

And all of my carboys have their sizes on the bottom (part of the glass mold).