potassium metabisulfite [puh-TAS-ee-uhm meht-uh-biSUHL-fite]

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A white powder or salt containing approximately 57 percent SULFUR DIOXIDE. Potassium metabisulfite also comes in tablet form, known as Campden tablets. Meta, as it's also called, is dissolved in warm water before being used. When stirred into wine or MUST, it reacts with natural ACIDS to release sulfur dioxide, which protects wines from unwanted bacteria and OXIDATION.