Copper Sulfate (CuSO4)
Definition - What does Copper Sulfate (CuSO4) mean?
Copper Sulfate (CuSO4) is a compound used as a fining agent for wines which have a "rotten egg" smell. This is from hydrogen sulfide that can form when yeast cells are stressed during fermentation. The copper works when it releases its own sulfur in the wine solution and "grabs on" to the sulfur connected to the hydrogen.
WineFrog explains Copper Sulfate (CuSO4)
Before adding copper sulfate to wine, it is best if the winemaker runs a test sample in a couple of wine glasses. The copper sulfate can be added by 1mL into a 45mL wine glass. The other wine in the second glass should not have any additives.
Once the copper is added, it can be swirled and allowed to sit for a few minutes. If after a few minutes the "rotten egg" smell has dissipated, then it is advised to add it to the batch of wine following other trials to see the proper amount needed. Too much copper is toxic.