Coffee stains on my jumper

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This morning I was looking at some of the jumpers that I have knitted to sell on Etsy https://www.etsy.com/your/listings?ref=si_your_shop To my annoyance one of the jumpers had a large coffee stain on the back. I immediately put the jumper in the washing machine to try and remove the stain. I now know that this was the worse thing to do because it compounds the stain. I looked in the net to try and found several suggestions.
Firstly I put white vinegar diluted with water on the stain but it did not work.
Secondly I was advised to dab baking soda (bicarbonate of soda) on the stain. At first the stain did not seem to move so I left the jumper soaking in water containing baking soda. Looking at the jumper some 30mnutes later the stain seems to have gone but I probably wont know for sure until the jumper is dry. I really hope this works because it really is my favourite jumper.