By law, wine is not required to have a contents label on the bottle. This is based on a old agreement between the wine lobby and the US government. As one of the only major food groups without a content label, consumers are left in the dark about what is in their wine. And, since there are 76 legal additives approved for use in winemaking by the government, wine is usually an industrialized, sterilized shelf product, not a natural one.
The only way to really know what is in your wine is to send a sample to an independent lab to analyze it.