A copper-sulphur compound (old name is copper vitriol), which presents itself as a powder of transparent blue crystals; without water content this is white powder. It is used - often in combination with copper citrate and silver chloride - to remove the wine defects Böckser and Käsäseln (since the substance is undesirable in wine, it is removed by silica sol). The chemical used to be widely used for pest control of vines, potato plants and fruit trees. It is also used to dehydrate alcohol.
Copper sulphate is also a component of the Bordeaux broth, which used to be the main remedy for fungal diseases such as downy mildew. Today it is increasingly being replaced by synthetic fungicides. In some countries, such as Germany, copper sulphate is now banned as a pesticide because many soils have been excessively enriched with copper, which is harmful to health in higher quantities, through decades of excessive use. See also under agents used in winemaking.