a question about degassing and acidity levels

[BernardSmith]

When CO2 dissolves in water it produces carbonic acid. How acidic is carbonic acid? Does degassing reduce the level of carbonic acid? Will a reading of the pH and TA before degassing be very different from a reading taken after degassing? Will this be significant enough to have an impact on the amount of free SO2 the wine will need?

 

[robie]

When CO2 dissolves in water it produces carbonic acid. How acidic is carbonic acid? Does degassing reduce the level of carbonic acid? Will a reading of the pH and TA before degassing be very different from a reading taken after degassing? Will this be significant enough to have an impact on the amount of free SO2 the wine will need?

Where are the resident chemists when you really need 'em?

 

[JohnT]

No idea about this one. A very excellent question!

 

[ibglowin]

Carbonic Acid is formed by this Rxn: CO2 + H2O -> H2CO3 (note it requires H2O to be formed, not EEOH)

It exist only in solution so when you degas you are removing CO2 (gas) and NOT Carbonic Acid, thus there no change in pH.

Those two Protons (H+) want to dissociate and hook up with something else stronger.

 

[Deezil]

IB,

Just trying to wrap my head around this - i read a little bit but it wasnt enough to respond in an answer, for Bernard... And most of what i read (theres very little i could find on wine) related to either soda pop, rainfall or our blood.. So i may be a bit abstract / off...

CO2 + H20 = H2CO3

While CO2 doesnt change pH, what i read says that H2CO3 can (albeit a 'weak acid'). And its practically impossible to get ALL of the CO2 out of wine (at room temp).

Theorize with me for a second...

Say you make a fruit wine (usually water added for one reason or another), it ferments fine - assuming it makes CO2, pushes out a bunch while some forms carbonic acid - would it make sense that, in the end, since you cant remove all the CO2 at room temp, that a greater majority of the bound-up CO2 in carbonic acid would be left in solution, and the free/dissolved CO2 would escape first? Seems like this could result in a pH change, sometimes seen during a fermentation..?

The pH would change during fermentation due to the creation of carbonic acid, and would remain the same because degassing would remove free CO2 first and potentially not unbind H2CO3.... ?

How far off am i?

 

[DoctorCAD]

Carbonic acid is what you "feel" on your tounge as a tingling when you drink a carbonated drink.

We dont want that "feeling" with wines.

Since carbonic acid doesnt hurt your mouth, I'd guess it pH isnt too far from neutral.

 

[GreginND]

It is an equilibrium. The formation of carbonic acid is a reversible reaction. Thus, if you remove co2 from the solution (degas) you will shift the equilibrium toward more co2. That is, if you remove co2 more carbonic acid will decompose back to co2 and water.

So, yes, degassing can result in reducing the amount of acid. But I don't think the amount of carbonic acid is significant enough to shift the pH much.

 

[ibglowin]

Not so sure about that one. Carbonic acid is a weak acid. It exist in everything from soda pop to rain to blood. Protons (H+) are the basic currency in chemistry. They are constantly coming or going from one molecule to another trying to reach an equilibrium. So if CO2 leaves as a gas, the same amount of Protons (H+) are left behind in the wine. Thus no change in pH.

 

[GreginND]

Not so sure about that one. Carbonic acid is a weak acid. It exist in everything from soda pop to rain to blood. Protons (H+) are the basic currency in chemistry. They are constantly coming or going from one molecule to another trying to reach an equilibrium. So if CO2 leaves as a gas, the same amount of Protons (H+) are left behind in the wine. Thus no change in pH.

Not quite right. When Carbonic Acid (slightly acidic) decomposes it produces CO2 and H2O. The protons are on water and are neutral. You are changing the acid strength of the solution. The process is driven toward more neutral by loss of the CO2 gas (e.g. it shifts the equilibrium)

 

[ibglowin]

Alright thinking way to hard for a Saturday! Since carbonic acid is produced from a Rxn with H20 it makes since that the breakdown would be the reversal. Since there is way much more pure CO2 in the wine than carbonic acid it also makes since that you would not see much if any increase in pH change due to degassing.

 

[GreginND]

Alright thinking way to hard for a Saturday! Since carbonic acid is produced from a Rxn with H20 it makes since that the breakdown would be the reversal. Since there is way much more pure CO2 in the wine than carbonic acid it also makes since that you would not see much if any increase in pH change due to degassing.

Right. I think degassing (thus reducing carbonic acid) will show in your TA measurements more. Affect on ph will be negligible.