if opening a bottle makes it go off then why doesn't bottling it after fermentation?

[ThePrisoner]

If you open a bottle of wine and leave it, it will go off within a day or 2.
How come this doesn't happen when you bottle it after fermentation?
I know of some places where you can bottle your own wine and cork it.
Also, when you are transferring your wine from barrel to bottle, it is exposed to air, so why doesn't it go bad in the bottle?

 

[salcoco]

normally so2 is added to wine before bottling and it scrubs the wine of any oxygen. wine that has been bottled for some time loses this so2 protection, so that when exposed to air it picks up spoilage bacteria. if wine that has been fermented and not had so2 added at proper dosage it will also spoil after a period of time. the addition of so2 at the proper dosages is the key and air exposure is the other problem.

 

[Turock]

This is why it's important to have a proper level of free SO2 in wine for preservation. The ideal method is to test for free SO2.