Prevention of copper and iron turbidities in wine

A search was conducted for a satisfactory substitute for potassium ferrocyanide in removing copper from wine to prevent formation of copper casse, at present the most important problem in wine stabilization. The most promising among the relatively nontoxic organic compounds tested was rubeanic acid. Cysteine and related sulfhydryl compounds and ascorbic acid precipitate excess copper, but further tests under winery conditions are needed. Aside from potassium ferrocyanide itself, the only other material that gave satisfactory results was an adsorption complex of potassium ferrocyanide and Prussian blue. Properly prepared and used—possibly with the addition of denatured protein—this complex would avoid contamination of the wine with ferrocyanide. Neither it nor rubeanic acid was as effective as the soluble ferrocyanide in removing iron from wine; but iron casses if troublesome might be dealt with by other means.