Ascorbic acid: often used as an anti-oxidant, available as a powder. Prevents fruits from turning brown due to oxygen exposure. When added to wine, ascorbic acid has only a very brief effect on the wine itself. It works by attaching itself to any dissolved oxygen in the wine and quickly converts it to a compund called dehydroascorbic acid, which is inactive and harmless. Within 48-72 hours it is completely inactivated and serves no further function. Winemakers can benefit from its use as an antioxidant during racking and bottling, where significant amounts of oxygen can be introduced into the wine during filling and splashing. It is usually used in conjunction with sulfur dioxide to provide an additive effect in preventing oxidation of wine. Usual dose is 1/2 to 1 teaspoon ascorbic acid powder dissolved in a little water and added to 5 gallons of wine. Sulfur dioxide concentration should be at least 25 ppm.