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Canning -- Vegetables
What causes a yellow precipitate in home canned asparagus?
A bright yellow crystalline substance may appear on the bottom of the jar of home canned asparagus. This yellow precipitate is rutin, a pigment naturally occurring in asparagus. At room temperature, rutin is not very soluble in water but at the higher temperature reached in canning the pigment dissolves. If enough of it dissolves, a supersaturated concentration may result when the liquid cools to room temperature. It then precipitates (the process of separating a substance from a solution as a solid) and is noticeable on the bottom of the jar. If your water is high in iron, the precipitated rutin may be gray to black. The product is safe to eat. PREPARED BY: Angela M. Fraser, Ph.D., Associate Professor/Food Safety Specialist, and Carolyn J. Lackey, Ph.D., R.D., L.D.N., Professor/Food and Nutrition Specialist, North Carolina State University (August 2004)