To clean grape stain on carpet:
1. Straight away start to blot up the stain with a wet sponge , operating from the outside go in direction to the inside if you wish to not extended the stain .
2. Use right lemon juice to the stain then blot up with dried towel .
After the stain is started to vanish a bit , apply a gentle bristle scrub to brush in extra lemon juice .
3. In case lemon juice is not effective try white vinegar .
Continue doing and blotting away the liquid until the mark is removed .
Later on you may deal with the area with spray in carpet foam cleaner to remove away the remains .