I have several old coffee stains on a carpet. Googling "coffee stain removal" reveals a variety of suggested cleaning substances-- vinegar, baking soda, laundry detergent, etc. I have used all of these on stains in the past to varying success, but always have a hard time totally eliminating the stain. Typically the instructions suggest iterative applications of the substance, and I usually end up with a huge pile of wet, wadded-up paper towels, each tinged slightly brown from the tiny amount of coffee absorbed.
What is the most effective way to remove old coffee stains from carpet using common household chemicals? Chemically, why is this the most effective means?