Copper Sulfate, liquid. This material is used to remove hydrogen sulfide and other reduced sulfur compounds which are the source of 'rotten egg' like smells. For best results use as soon as possible after the end of fermentation, if racking the wine once or twice during fermentation didn't eliminate the problem. Avoid adding excess copper. Use bench tests to determine the minimum effective dose. If in doubt about excess copper, contact us or have the wine tested for copper levels. If the wine takes on a bitterly astringent taste you have excess copper.