BeerBorg

Currently I have about 3.25G fermenting in a 6G carboy. I've done this a few times and never worried about the headspace because I know the CO2 will blanket it and protect it from any oxygen in the carboy (referencing discussions in BlackDuck's thread on a similar topic).

After pitching the yeast on Sunday I checked it today when I got home and found the airlock actually bubbling. Clearly the batch has produced enough CO2 to push air out of the airlock so it got me thinking......just how much CO2 is produced? There must be some formula based on volume and gravity, right?

I have no worries here, just curiosity. I'm off to search the interwebz now.

It doesn't need to produce much. Just enough to displace some of the air that is in there.

<smacks head> Actually, that's a great point. My initial thought was that the entire headspace was filled with CO2 and THAT was what was getting pushed out but you're right - it was just displacing the air. But my question stands. How much of that empty space in my carboy (roughly 3G of space) is CO2 versus oxygen?

And....apparently this is a quick and easy Google search to find the answer:


I'm going to go measure my carboy to find the volume in cubic feet to figure out just how much I'm creating here.

I'm not following why you are measuring your carboy? The Cubic Feet in that chart is how much CO2 is produced in volume. The Pounds is in weight. Neither has anything to do with the size of your vessel. Just OG and Attenuation matter. Even the lowest number on that chart is going to total displace any air in any 5 or 6 gallon carboy.

My plan was to measure the carboy to determine the volume so I could figure out how much volume it holds. Then I was going to use the chart to determine how much co2 is produced to see if all the air gets pushed out and nothing but co2 is left.

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Well, I ferment in a 6.5 gallon carboy inside of a 5.0 cubic foot chest freezer. It'll fill the chest freezer with CO2 in only a fraction of a fermentation.

Don't measure your fermenter, just convert gallons to cubic feet.

There is enough that a lot breweries recover the CO2 by way of a spunding valve, and use it for carbonating their beer. The claim from some is it can save a brewery nearly 75% in purchased CO2.
http://www.essentialbrewinginabag.com/2 ... valve.html

All I know is that when I open the cooler where I keep my LBK fermenting, I get a big whiff of C02 that literally takes my breath away. As in, it displaces the oxygen for a second. I'm in such a rush to get a sniff of that freshly fermenting beer, that I get a C02 blast. I'm weird like that.

If I interpret this correctly, the carboy holds approximately 2 cubic feet of air. A 5G batch of wort at about 1.047 produces roughly 12 cubic feet of CO2 @ 65% attenuation.
So, with a 3.5G batch, I'm somewhere in the 7 cubic feet range which easily fills the head space a couple of times over.

Interesting.

I think your carboy holds less than 1 cubic foot. I searched 5 gallons to cubic feet and came up with .67. That fits my rough estimate: 1 gallon weighs about 8lbs, 5 would be 40#. 1 cubic foot of seawater (heavier, but I know that #) weighs about 64lbs, fresh water is a bit lighter, say 60ish. 40/60=2/3 ie .67

Yeah, you're right. I found a quick conversion of gallons to cubic feet and 6G = .80 cubic feet. So if I'm taking up roughly 50% of the carboy with beer that leaves ~.40 cubic feet of oxygen when I pitched the yeast and set it in my chamber. According to that chart I'm generating about 5-6 cubic feet of CO2 so MORE than enough to fully replace all of the oxygen which was the heart of my initial curiosity.

Thanks for the chatter guys.