Coffee stains on carpet aren't difficult to remove if you act quickly. Here's a good rule of thumb: to remove carpet stains effectively, it's important you get to the task immeidately upon spilling, if you don't you're more likely to incur permanant damage. Dab at the stain with vinegar or club soda until it's removed. If you waited too long and the stain has set in, you should still be able to remove the stain by using dry-cleaning solvent. Blot until the stain is lifted.