Mercaptans are complex sulfur compounds that can develop in wine. They are mostly unpleasant smelling chemicals with aromas often described by characteristics like burnt rubber, cooked cabbage, onion, and rotting flesh. Mercaptan characters must be treated as quickly as possible in wine with copper sulfate as they can develop into chemical forms that become very difficult to remove if allowed to remain. A combined treatment of copper sulfate with ascorbic acid is required if more complex mercaptans develop. This treatment can be a very slow process requiring a month or more to resolve the problem and may not be effective. Mercaptans are mainly the result of untreated hydrogen sulfide problems in wine.