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A blueberry stain is one of the easiest stains to see, and depending on the fabric, one of the most difficult to treat. This also applies to other deep red-colored fruit stains such as those made by cherries, grapes, blackberries, cranberries, and raspberries. These fruits stain on two fronts with dye and sugar. The strong red dyes leave their mark immediately and the sugars turn yellow with heat and age.
The Key: If at all possible, treat these types of fruit stains while they are still fresh, the sooner the better. Scrape and blot up all you can, then immediately and repeatedly sponge the area with cool water until no more color is being removed. Old stains on valuable pieces of clothing or fabric should be taken to a cleaning professional.
The Caution: Don't launder fabrics in hot water and don't use real soap. Both will set fruit stains. Other than the boiling water method listed below, don't heat-treat the fabrics, including hot-air drying or ironing, until the stain is completely gone. Heat treatments will set the stain and are likely to make it permanent. For "fresh" stains on cotton, linen, and other sturdy white or colorfast fabrics, try the boiling water method. For more delicate fabrics, try one or more of the gentler procedures. Always pretest all treatments on a small area of fabric for colorfastness/durability before fully committing.
Five Methods for Removal
Laundry Pre-treat: Flush the stain with cool water. Mix one tablespoon of white vinegar and 1/2 teaspoon of liquid laundry detergent with one quart of cool water. Soak the stain in the vinegar/detergent solution for 15 minutes. Rinse with cool water. If the stain remains, sponge with rubbing alcohol and rinse thoroughly before re-laundering.
*Wet spotter - mix 1 part glycerin, 1 part white dishwashing detergent, and eight parts water. Shake well before each use. Store mix in a plastic squeeze bottle.
**Tamping a stain - removal technique using a small, soft-bristled brush, that is effective on durable, tightly woven fabrics (it may damage delicate or loosely woven, fabrics.). Place the garment on a solid work surface. Hold the brush (a small toothbrush works well) 2 or 3 inches above the stain and strike the stain repeatedly with the brush using light strokes. If the bristles bend, you are using too much force.
By EllenB 
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Here are questions related to Removing Blueberry Stains From Clothing.
What will remove blueberry stains from clothing?
By Lillian from Lincoln, CA
This is great. I thought my son had ruined his khakis as well. I scrubbed vinagar into the stain them poured boiling water over it and it just rinsed away. Best laundry tip since blood and peroxide!