Bound SO2

[berrycrush]

What does bound SO2 tell us about a wine? Say wine A has 15ppm free SO2, 35ppm bound SO2; wine B has 15ppm free, 85ppm bound. B has more oxidation?

 

[GreginND]

This paper from Morewine helps explain SO2.

http://morewinemaking.com/public/pdf/so2.pdf

In essence, the bound SO2 is that sulfite that has reacted with other things in the wine. It is no longer available for protecting the wine. You need to have the free SO2 for protection.

 

[seth8530]

I have heard that excessive bound SO2 can lead to HS2 fermentation during fermentation. However from a protection standpoint, bound so2 is spent free SO2.

 

[berrycrush]

How often do winemakers add SO2 to the barrel? How much total SO2 ppm is typical by the time the wine is out of the barrel into the bottle?

 

[GreginND]

Best practice is to try to maintain a minimum of 0.5 ppm molecular SO2 for reds and 0.8 ppm molecular SO2 for whites. It is hard to predict how much one needs generally because it will depend on the pH of the specific wine and how much it needs to react with other components while it is protecting the wine.

 

[Fsim]

GreginND is spot on but unfortunately you need to test and see how much free SO2 is in your wine. There is the expensive method of buying a tester for a few hundred or the Aeration-Oxidation method which you can make yourself which is what I do.

 

[berrycrush]

When you open a bottle and find free SO2 is zero, what do you do? Say you have 30 bottles from the same batch.

 

[Fsim]

You should test prior to bottling. What was your PH or are you hypothetically saying.

 

[GreginND]

I would drink it!

I don't see any sense in opening up 30 bottles. They are sealed and oxygen contact is minimal through the cork. You'll oxidize it a lot more by opening and adding more sulfites than just leaving it alone. Many wines age for decades after SO2 is depleted. I would not expect your wines to go downhill over the next couple years sealed.

 

[berrycrush]

By regulation, total added SO2 should be within 350ppm, correct? In a normal batch aged in barrel, do you actually reach that limit? Imagine the taste of the wine with 350ppm SO2, would that be drinkable?

 

[seth8530]

I think the rule is on free SO2.. Don't quote me on that. But, either way hitting 350 ppm bound or free so2 would be an impressive feat.

 

[berrycrush]

I found this study posted online showing the analysis of a batch of Australian wine at the time of bottling. Their total SO2 is 87ppm, free SO2 at 30ppm. Is this typical per your experience?


Table 1 Chemical Analysis of Bin 389 at point of bottling (11/12/1997).
Anolyte Concentration Anolyte Concentration
Residual Sugar (g/L) 1.7 Fe (mg/L) 2.1
Alcohol (%) 14.2 Ca (mg/L) 55.5
Free SO2 (mg/L) 30 Na (mg/L) 98
Total SO2 (mg/L) 87 K (mg/L) 1217
pH 3.54 Acetaldehyde (mg/L) 20.5
Titratable Acidity (g/L) 6.5 Ethyl Acetate (mg/L) 79.5
Volatile Acidity (g/L) 0.73 Methanol (mg/L) 135.5