Here's why:

* Hot water sets stains: Heat can actually set the stain into the fabric fibers, making it harder to remove.

* Cold water loosens pigments: Cold water helps to loosen the pigments in grape juice, making them easier to remove.

Steps to remove a grape stain:

1. Blot the stain: Use a clean, white cloth or paper towel to blot up as much of the grape juice as possible.

2. Rinse with cold water: Rinse the stained area with cold running water.

3. Apply stain remover: Use a stain remover specifically designed for fruit stains. Follow the instructions on the product label.

4. Wash as usual: Wash the garment according to the care label.

Additional tips:

* Treat the stain as soon as possible.

* Avoid rubbing the stain, as this can spread it.

* If the stain persists, repeat the steps above or consult a professional cleaner.

Note: Always check the care label of the garment before treating any stains.