Using innert gas in a large head space

The biggest problem with headspace is actually the exchange of gas through the airlock. gas dissolves into the liquid in the airlock on the atmospheric side and then is released on the wine side.

that reastion is a concentration controlled process. That is the oxygen will diffuse across the airlock barrier to equalize the O2 level in the headspace at ~20%. the airlock will NOT stop that. it only slows it down. The concentration of oxygen in the headspace WANTS to go to 20%. So the gas in the headspace will equalize with the atmosphere eventually. That gas can then dissolve into the wine causing oxidation. The larger the headspace the more gas you can accomodate in the carboy and the faster the oxidation will take place.

That is why i put metabisulfite in my airlocks and keep it fresh (once a month or so). the SO2 gas will react with any O2 that dissolves in the airlock and take it out of solution (of course by doing that it just speeds up the rate that the gas dissolves in the solution, becasue it too wants to equalize wiht the atmosphere).

Ray Calvert wrote "This topic comes up fairly frequently. I would like to throw out two issues I have with using gas to top up. 1) One of the questions is how much gas is needed. Someone recently said that we need to remove all the air. Well that is not possible."

Ray - I believe you can remove essentially all the air from a carboy and especially from a Corny keg if you happen to use them. This technique is probably more suited to the kegs. Fill the keg brim full with water. Seal. Pressurize with CO2 (or the gas of your choice) while allowing the water to escape through the tap. When all of the water is gone the keg is totally filled with gas. For a carboy siphon slowly while filling the top space with gas. I guess you could use the gas to force the water out of a carboy using a two-hole stopper but I agree with those who caution against pressurizing glass containers.

That said I would never trust wine to a partially filled carboy or Corny keg. Learned the hard way years ago. However, several winemakers in our club do this and still make pretty good wines.

Can't comment on the air lock issue. I only leave about 1/2 inch space beneath the stopper in carboys and I don't see much movement in the air lock liquid...I use Vodka.

Bill Frazier Olathe, Kansas USA

Bill, how do you keep the Vodka from evaporating?

The number I heard was approximately 7 times the volume of the headspace. Commercially, gas purging is done using an oxygen sensor to determine when the air has been sufficiently displaced.

Tom S

"Bill, how do you keep the Vodka from evaporating?"

Paul - The vodka doesn't evaporate quickly in my cellar. But, I'm down there about every day and check on the carboys. I just add a little more vodka if an air lock seems low.

Bill Frazier Olathe, Kansas USA

Of course, you have to quality control the vodka to make sure it is still OK ; )

Good point Droopy. That is a third problem. Diffution due to concentration differences. I don't know that it is a larger problem than the other two but it is a different problem.

Good point William. Don't know how many migth use the meathod but it is a meathod that should work.

Here is a suggestion that I thought of over the weekend. See who can polk holes in it.

The reason you use an airlock rather than a solid bung is that that two things could possibly happen. First it could start ferementing again and that would be bad. But if you have stabilized it you should be able to stop that problem.

Second, you need an airlock because of pressure built up due to temperature changes. Wine is basically an incompresible fluid. Air is very compressable. Temperature changes can cause 6 gallons of wine to change volume by several cubic inches. When it does it is going to compress the air in the head space by an equal amount. If there are 4 cu.in. of air in the head space and the wine expands by 2 cu.in. (this is very possible), then if you have an airlock, the pressure is maintained at 1 atm. But if you have a solid bung, the pressure will go up to 2 atm or it could go higher. The bung will blow out and your wine will oxidize if you do not catch it or, worse, the jug will shatter.

But if you have 4 gallons of wine and a gallon (231 cu.in.) of head space filled with inert gas, then if the wine expands by 2 cu.in. this will yeild only a 1% increase in pressure not a doubling. Yes the gas will try to expand and will yield a little pressure increase as well but not too much.

Maybe the thing to do if you have a large head space filled with inert gas is to do the opposite of what is noramlly recomended when topping up, inother words, abandoned the airlock and use a solid bung. This would address all 3 issues raised.

Comments.

Well a couple of things, you are assuming that a the wine will change volume to an extent that I do not think it can. I have never seen a full carboy fluctuate more than 1/4 or so.

The second assummption you make though is that the solid stopper is a complete seal and impervious to pressure changes, that is that the bung will resist a pressure change of 1 or more percent.

When in fact, the pressure will bleed out between teh stopper/carboy interface. Airlocks get around this by allowing the pressure to fluctuate. If you stop it up, the air will just seep around the sides of the stopper. If you can creaste a strong enough seal that will be fine, but you are looking at a bottle cap type seal then.

Better yet, fill it up to the top and put it in a thermostable location to stop the fluctuaion to begin with, just like you would with a corked wine.

This is not assumption. Coefficients of expantion are valid. Coefficient of expansion of wine will be a little different than water but not much.

A solid rubber stopper will seal very well and you should have no leakage around the rubber. Infact the main arguement against useing them when a carboy is topped up is that the pressure change can crack the carboy or it will totally blow the bung out. That is what I am trying to get arround.

I agree, that would be better but such environments are rather expensive. I may build one when I retire but not right now..

Ray

Sure coefficients of expansion are valid. But you are assuming a temperature fluctuaion of at least 10 degrees F (from about 77 to 68) to get a volume change of several cubic inches. The SG of water only changes 0.0012% in that range. Which would give you 1.6 cu in expansion.

Even in my old place built in the 20s I did not see a temp fluctuation that bad.

The 7 volumes of headspace purge sounds about right to be 'safe'.

Under 'ideal conditions' in a wine barrel or carboy or wine bottle, the minimum of purge volume using Argon would be 3 volumes of headspace (purge tube outlet just above the liquid level and very slow argon flow rate, on the order of 50ml per minute [3 cubic inches per minute]). Under these ideal conditions, the much denser argon displaces the air/oxygen without too much mixing.

Nitrogen purge gas is much less effective than argon because it mixes much more into the air inside the container, rather than displacing it (air and nitrogen gas have almost the same density, cuz air is about 80% nitrogen gas).

A beer keg or soda syrup container would not purge as well as a wine keg or carboy, since they have 'stagnant' (dead) spaces. The outwardly convex (bowed) shape of the wine barrels minimizes dead air spaces. The bell-shape curve of the top portion of a carboy/wine bottle accomplishes the same thing.

Gene

And the water portion of the vodka evaporates slowly. As long as there is at least 10 percent alcohol in the airlock mixture, nothing harmful to us will grow in the airlock. [86 proof vodka is about 40% alcohol; 100 proof is about 50% alcohol]

Good idea to top up the airlock with vodka once a week. I use pure glycerine myself, so I never have to top up the airlock (over a year and no noticeable evaporation).

Gene