Degassing - one more question

[BernardSmith]

Is it possible that there is some relationship between how much effort and time is needed to degas wines (whether kits or those made from scratch) and the amount of time spent in agitating the wine in the primary fermenter (as we break down fruit caps and introduce air? Yeast produces CO2 as it converts sugars into alcohol and this CO2 is dissolved in and absorbed by the must or wine. It's not under a great deal of pressure but CO2 is heavier than air. Does anyone know if it is easier to degas those wines we have spent more time agitating and mixing in the first week or so or whether it makes no difference? In other words, is it possible that the kit manufacturers (and others) are basing their rule of thumb about how much time and how much effort is needed to degas on a set of assumptions about how much CO2 has been evacuated during primary fermentation

 

[rjb222]

Yes there will be less gas in a wine that has been punched down.

 

[Minnesotamaker]

I wouldn't think that punching down during primary would have much effect on gas, unless the action were to release compounds into the liquid that would make it more likely to hold gas.

Here's how I understand it. Your must is a liquid. To the CO2, the liquid is like a vessel. As the yeast produces CO2, it is released into the liquid and dissolves. Your wine (as a gas vessel) has the ability to hold a certain amount of CO2. When the wine "gets full" of CO2, it starts to "spill over" (or in this case, push out of suspension, rise to the surface, and escape). Keeping your "vessel" under pressure allows the liquid to hold more CO2, but as soon as the pressure is released, the CO2 will begin to escape (just as you see with an opened can of pop). Therefore, since your punching down is done during the primary stages, the agitation WILL drive off some of the dissolved CO2, but it would be quickly replaced by the active ferment. After moving the batch to the secondary, your batch, assuming there is still some ferment, will fill with CO2 and reach an state of equilibrium and excess CO2 will push out the airlock. Once ferment stops, any CO2 that escapes due to agitation, pressure or temperature changes, or natural expiration, will not be replaced by new CO2 and your wine will reduce it's levels of carbonic acid.

 

[TonyP]

I agree with Lon's assessment. CO2 extracted from the wine during primary fermentation activity would be replaced by CO2 later in fermentation.

Beyond that, somebody tell me if I'm wrong, but I believe dissolved CO2 increases when the wine is under pressure during secondary fermentation. Thus, most of the dissolved CO2 extracted during degassing was created during secondary fermentation, not primary.

 

[BernardSmith]

I am not a chemist or a physicist but I believe that for every liter of wine produced you will also produce about 140 gms ( almost 5 oz) of CO2 or roughly 8 lbs of CO2 for every 6 gallons (US) of wine. That seems like an enormous amount. Am I way off base with my estimates?
If in your primary the must changes from a gravity of 1.090 to a gravity of 1.010 then almost all the sugar has been converted before you rack into a secondary carboy. That means that almost 80 percent of the total amount of CO2 is produced in the first week (about 6 lbs). Certainly the yeast is still producing CO2 in the secondary but an SG of between 1.010 and 0.990 is only 20 percent of that produced in the primary. If much of the CO2 produced by the yeast in the primary is transferred into the secondary and it is dissolved in the wine then you are going to need to expel far more CO2 than if it is only a little more than the 2 lbs produced while the wine is in the secondary.
That said, Lon and Tony P suggest that the wine is under pressure in the secondary. I don't think it is. Or rather the pressure the airlock exerts is tiny. How much pressure does an inch or two of water (from the air lock) exert on the wine? It cannot be that significant otherwise we would be tying down bungs to prevent them from flying off as the CO2 under pressure would be pushing the bung out of the neck... Or does wine yeast only convert sugars at the bottom of the carboy so that the pressure is from the height of the column of wine in the carboy? People who splash rack from primary to secondary or who rack under vacuum are removing a great deal of the CO2 as the wine enters the secondary but those who place an airlock on the primary and then siphon into the secondary must be transferring almost all the CO2 the yeast produced (except for the gas that bubbled through the airlock). Removing close to 8 lbs of CO2 rather than 2 pounds must involve more time and much more effort...

 

[Dugger]

It has been my experience with wine skins kits that the daily punching down of the skins (I stir them around a bit too) releases tons of CO2 at the time and seems to result in much less CO2 when I degas. I cannot empirically say there is less gas but it sure seems like it.

 

[TonyP]

Bernard, sorry to be a contrarian on this, but I see some of it differently. Clearly yeast activity creates substantial CO2 during fermentation. However, most of the CO2 is lost through the airlock or otherwise escapes during fermentation. It is only the captured (dissolved) CO2 that must be removed during degassing. The fact that this, residual CO2 is usually a small amount is verified by the fact that degassing alone doesn't generally require a substantial topping up. (Removing 8 lbs of CO2 would, obviously, require substantial topping to eliminate the head space.) Of course, sometimes degassing creates a volcano of wine, so dissolved CO2 is not always di minimus.

I agree fully that much of the CO2 is produced during primary. However, CO2 is not the issue. Only dissolved CO2 - CO2 that does not escape - must be removed.

On pressure, it is not the pressure created by the airlock that's important. You're correct, that is not significant. It's the internal pressure of the wine and the CO2 that causes the CO2 to dissolve. That pressure is significant and, if you're not certain, replace the airlock with a solid bung and see what happens. Wine makers often have corks pop on bottled wine due to CO2 created by continuing fermentation.