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Practices -- Cooking
Why does garlic turn blue-green when cooking with butter and lemon?
Garlic contains sulfur compounds that might react with copper to form copper sulfate, a blue or blue-green compound. The amount of copper needed for this reaction is very small and is frequently found in normal water supplies. The other sources of copper might be the butter or lemon juice. The garlic is safe to eat. To prevent this in the future, do not refrigerate garlic and store the bulbs in dry air for 32 days at above 70 F to 80 F before use to prevent formation of the green or blue-green pigments.