Coffee spills are very common causes of rug stains. If you accidentally knock a cup of Joe onto your carpet, don’t be surprised if you call your professional rug cleaner and they ask whether the coffee is regular or decaf. They are not practicing for a side job waiting tables. It actually does matter.
Regular coffee contains tannins that darken the brew, but usually don’t stain if the coffee is dabbed up right away. However, during the decaffeination process the tannins are removed. This has the effect of lightening the coffee color, making it less appealing to coffee drinkers. To compensate, the processors add dark dye to the decaf grounds. This makes the brew look tastier, but it also complicates spill cleanup. In fact, because of the dye, fully removing set-in decaf coffee stains requires a professional with heated, chemical dye remover.
If you do spill coffee on your rug, regardless of type, dab it up with a rag and clean water immediately. And consider switching from decaf to regular.