I'm a massive fan of manual brewing, especially pourovers. I know this is a fundamental process of the manual brew method, but lately I've been noticing that a lot of people aren't rinsing their filter paper sufficiently.
It's really important to rinse your filter paper. It removes paper odours, taste and dust from the paper and makes your brew taste a lot better. It also warms your vessel up so that your brew doesn't lose much temperature.
Next time you brew, taste the water from your filter paper rinse and you will understand that those paper flavours are quite strong and taint your brew.
I've done a little experiment with different types of paper filter. I've chosen the Chemex, Hario V60, Aeropress, Melitta Natural, Kalita Wave and a glass of hot water as my control. The aim is to cup these papers and give you a description on what they all taste like.
All the filter papers had a very similar taste to them (apart from the natural filter paper which changed the colour of the water and was the most disgusting). The big surprise was the Chemex paper. It had a cardboard taste and smell. Very similar to a damp cardboard box. The texture of the water also ended up a lot thicker (if that makes sense?). The Aeropress paper tasted like envelope glue that you lick to close it up. Not as intense but traces of it. The Hario V60 and Kalita Wave paper filters were by far the closest to the water control. It was very hard to split them but if I had to, the Hario V60 would probably take the chocolates.
After tasting all the different papers, I can confirm that it's extremely important to rinse your filter paper throughly before you start brewing. It can heavily impact the flavour of your coffee, and you don't want that!