SO2 Drop in Barreled Wine

Yes, that's perfectly normal - especially in a new barrel. Oxygen is coming in through the staves (while water and alcohol are going the other direction). It helps soften the tannins, but it also reacts with the free SO2 to form SO3, which is the anhydride of sulfuric acid. The amount is very small and isn't noticed within the acid structure of the wine itself. You'll probably want to check and adjust the free SO2 about 3 times per year. BTW, getting proactive about it and setting the SO2 extra high in anticipation of its loss is not recommended.

Tom S

Could you elaborate on the last sentence Tom? TIA, Guy

What's to elaborate? If the wine needs 50ppm free SO2 to yield 0.8ppm molecular SO2, don't set it at 70ppm knowing that it'll drop eventually while in barrel. Set it at 50ppm.

Tom S

The thing to elaborate would be WHY?

I was a little curious my own darn self, having asked this question before, and not gotten an answer (ro at least nto one that I remember).

Thanks!

Dave

If you set the free SO2 extra high, how are you going to monitor the progress of the wine by tasting it as it ages? Wines above 0.8ppm molecular SO2 are not very taster friendly.

OTOH it's OK to set the free SO2 high in the _topping_ wine. That'll tend to slow the decline in the barrel if you top regularly.

Another thing to consider is that you may decide to bottle sooner than you expected, so if you set the free SO2 high in the barrel it may still be too high when it's time for bottling. Better to bring the free SO2 up at bottling time.

Tom S