Why does lemon juice prevent cut apples from turning brown and vinegar doesn't? Answer: Cut apples turn brown because of a reaction called oxidation.  Oxygen in the air reacts with a natural substance in apples called phenolase and turns the cut surface brown.  Mild acids like lemon juice can stop this reaction; tossing cut apple chunks with a little lemon juice will keep the apples from turning brown.  Vinegar which literally means "sour wine" goes through a fermentation process, which makes it stronger than lemon juice.  The key here seems to be the mildness of lemon juice. - Answer provided by Ask Dr. Universe Email Question    Print Question

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