Anybody ever tried intentionally doing a 7+ gallon batch in a 6.5-gallon carboy?

My first few batches, I didn't actually measure the top-off water, I just figured, "Well, my carboy holds X gallons, so if I fill it a few inches from the top, that must be X gallons." I later discovered, as many others have, that my carboys seem to hold something like X+0.5 to as much as X+1.5 gallons depending on the carboy. That explained why I was getting low OG readings on every batch. Since I have started actually measuring my top-off water, my OG is coming out within a couple of points of what I expected.

(I know some on this board don't believe it's possible to get an accurate gravity reading if you are topping off, but if that's true then I've been getting stunningly lucky in that when I accurately measure the volumes, I always get nearly right on what I was expecting)

So I just did a batch yesterday in my big carboy, and I'm looking at all that empty space at the top that I used to foolishly put top-off water in, and I'm thinking... why not just scale up the batch size?

I'll probably try this next time anyway, but I'm just wondering if anybody else has tried it and what their results were...

Seems reasonable, though might end up needing a blow off tube?

These days, I put a blow-off tube on 100% of my beers for the first few days. I used to try and guess whether I would need one based on the gravity of the beer, the type of yeast I used, and how full the carboy was -- but I had a streak of three or four in a row where I was always exactly wrong, i.e. anytime I put a blowoff hose on it stayed dry, and anytime I put an airlock on right away it overflowed. So I just do it all the time now, and swap in an airlock after a few days.

But yeah, that's sorta what I'm thinking -- why not, right?

If you fill it to the top, you're just gonna lose a bunch through the blow off

IrregularPulse said:

If you fill it to the top, you're just gonna lose a bunch through the blow off

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There's no way I'm going to lose 1.5 gallons through the blowoff, though, even if I filled it right to the brim (which I'm not suggesting).

The batches where I over-topped, they probably had 6.5 gallons in them at bottling time. I am guessing I could go a little higher even, probably get about 7 gallons, without losing more than a pint or two out the blowoff hose. Maybe I'm kidding myself...

I'm going to try this experiment either way, but I was curious if anybody'd already tried it. Well, besides me, since I already sort of tried this by accident when I over-topped.

jsweet said:

I'm looking at all that empty space at the top that I used to foolishly put top-off water in, and I'm thinking... why not just scale up the batch size?

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One big problem, once fermentation is well under way even if you use a blow off tube you will blow off a ton of beer.

I've accidently topped my 5 gallon carboy to 5.5 gallons with a blowoff and after fermentation is done, I have .25 to .5 gallons in the container that held my blowoff tube.

It would honestly just be a waste.

dallasdb said:

I've accidently topped my 5 gallon carboy to 5.5 gallons with a blowoff and after fermentation is done, I have .25 to .5 gallons in the container that held my blowoff tube.

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Really? Interesting, this is good to know. This has not comported with my experience of accidentally putting an extra half-gallon in, but this does make me wonder if I try to push it much further it could backfire just like some have suggested.

From what it sounds like you have a 6 or 6.5 gallon carboy and mine is only 5 so you may have more headspace than mine does.

In fact on my last 5 gal batch I barely filled over the 5 gal mark and still have a significant (.25 gal) amount of liquid blowoff.

Make sure you control the temps to the low end of where the yeast are happy, it'll help reduce the blow-off.

IXVolt said:

Make sure you control the temps to the low end of where the yeast are happy, it'll help reduce the blow-off.

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I usually ferment 64-68 degrees depending on my basement temp.

Those are good temps. I sure wish I had a basement!!