7.5 Gallon Carboys

[troutab81]

Long time beer brewery, first time wine.

I have 7.5 Gallon glass carboys. I think they will work well for primary, but what about secondary / refining? I've read you want no headspace, and I have a Winexpert kit that I think makes 6 gal. Do I NEED to get a 6 gal carboys or can I just get by with 7.5 and 1.5 gal of headspace for secondary? I have CO2 so I could fill before racking, thus eliminating oxidation? What about fermenting 7.5 gal in the primary with topped off water and using a blow off tube?

Please help

 

[troutab81]

Lots of auto corrects in that post... You get the idea

 

[cgenebrewer]

You want the correct amount of headspace once you remove the co2 barrier. If you can put an inert gas in the carboy it may work.

 

[Yooper]

It might work if you top off with inert gas and the gas doesn't disipate quickly out of the airlock. Generally, you want to match the batch size with the carboy size and leave no headspace in secondary.

 

[troutab81]

Is don't see how the CO2 could dissipate out of the carboy. That would mean something would have to leak in to fill the vacuum left by the exiting CO2.

Regardless, what are the issues with 1.5 of headspace?

 

[troutab81]

Sorry I'm transferring beer knowledge to wine. Is the headspace just for oxidation reduction?

 

[Yooper]

Sorry I'm transferring beer knowledge to wine. Is the headspace just for oxidation reduction?

Yes.

 

[Yooper]

Is don't see how the CO2 could dissipate out of the carboy. That would mean something would have to leak in to fill the vacuum left by the exiting CO2.

Regardless, what are the issues with 1.5 of headspace?

One of the things that drives me crazy on this forum is the talk of the "co2 blanket" that is supposed to constantly exist to protect beer and wine from oxidation.

Now, don't get me wrong- when fermentation is active, there is a ton of activity and c02 is being produced like crazy. It does work as a sort of a blanket in a way, protecting the beer/wine. But it also dissipates out the airlock. It's not there forever, and it IS replaced with other gasses without pulling a vacuum!

The thing to remember is that CO2 is a gas and follows the laws of all gases, which means it will act in accordance to the natural properties it is endowed with and react to environmental influences, but one gas does not push all other gases from a space just because it is heavier or colder or newly introduced.

In a closed environment, like a carboy with an airlock, CO2 created by fermentation will quickly fill the ullage and "push out" most of the air that was in that space through a process best thought of as pressurized dilution. But even after 5-6 days of vigorous fermentation and continuous bubbling away, if you measured the air in the ullage you'd be surprised to find there is still some oxygen, hydrogen, helium, etc. in there. You wouldn't think so, but there is. It won't be much, but there will be some. And the co2 will dissipate at an equal rate as all the other gasses. The Ideal Gas Law states that the gasses are always seeking equilibrium.

Anyway, in the short term, sparging the carboy with c02 will probably work. But it should be done again later if the wine will be in the carboy for any length of time, due to the Ideal Gas Law.

I'm no scientist, so for a scientific explanation, the Brew Science forum can help with an explantion of why this "c02 blanket" doesn't last indefinitely, or in fact very long at all. Here's some easy quick reads, though: The use of inert gas in winemaking

In short, gasses don't stratify by weight. If they did, we'd all die in our sleep when the "blanket of co2" covered us. How long the layer of co2 is above the wine is not indefinite, but it is protective while it is there.

 

[troutab81]

Thanks Yoop!

 

[DoctorCAD]

Best explanation of CO2 blanket, ever.

Yooper knows of what she speaks!

 

[Jsbeckton]

One of the things that drives me crazy on this forum is the talk of the "co2 blanket" that is supposed to constantly exist to protect beer and wine from oxidation.

...the co2 will dissipate at an equal rate as all the other gasses. The Ideal Gas Law states that the gasses are always seeking equilibrium.

Sure, but the environment is isolated by the airlock. So the equlibrium would be with the gasses within the control volume following the completion of fermentation or the initial conditions. These initial conditions contain very little O2. Now you need O2 to either come out of solution of your beer or to diffuse through the sanitizer, and through the airlock and into this environment.

I'm no scientist, so for a scientific explanation, the Brew Science forum can help with an explantion of why this "c02 blanket" doesn't last indefinitely, or in fact very long at all. Here's some easy quick reads, though: The use of inert gas in winemaking

I am not familiar with winemaking but I did read through this and had trouble interpreting the conditions. To me, on the read thorugh it sounded like the paper was talking about a "CO2 blanket" that was exposed to air, didn't notice anyting that sounded like an airlock condition but I may have missed something. If they didn't use those conditions, the paper is not very useful for this conversation because we are talking about two environents seperated by an airlock.

In short, gasses don't stratify by weight. If they did, we'd all die in our sleep when the "blanket of co2" covered us. How long the layer of co2 is above the wine is not indefinite, but it is protective while it is there.

The question is, is that time less or more than it takes to fill a carboy and replace the airlock after the initial "purge".

Anyone know of any studues specifically about oxygen diffusion through an airlock? I purge my carboys (when I do a secondary) and kegs prior to filling and have noticed no difference between beer that had more or less headspace.

 

[Jsbeckton]

Interesting paper about airlocks:

www.mocon.com/pdf/optech/Closures%20-%20Oxygen%20Passage%20Study.pdf

Seems if you use a stopper after fermentation instead of an airlock you can basically eliminate oxygen from diffusing into your fermentor. If you leave the airlock on make sure its free from defects but you will get some amount of 02.

Not really sure about the headspace question though. If you are getting a rate of 02 diffusion one might think that more headspace means less 02 concentration but not sure about the rate of diffusion change with headspace. Also there is the question of surface area which can be the same all the way until you hit the necking portion.

 

[SagamoreAle]

Id' splurge the $30 and get a 6 gal secondary.

Either way, put some metabisulfite in the airlock. Even after fermentation is over, the carboy will breath thru the airlock as the temperature in the room changes. The metabisulfite in the airlock ensures that there will be sufficient sulfur in the headspace to scavenge any oxygen that makes it in.

 

[H22W]

We have 6.5 gallon carboys and top up the headspace with other wine. Just whatever we find with similar characteristics.