Should I rinse paper coffee filters before use? I have never bothered to rinse my paper coffee filters before use, but some strongly recommend this. I did some experiments, outlined below, to test this. I don't find rinsing makes any difference, but there might be benefit that I don't understand.

My questions, in sum:


What's the best way to rinse a paper filter? Inside, outside, both? Soak? Hot or cold water?
How does it help? 
Bonus: What is being rinsed off? Are loose bits of paper really coming off the filter?


Of the many articles about this, most of them simply point to this Serious Eats article (e.g., lifehacker and the kitchn don't have much more content; others are chat/discussions without concrete conclusions or references). That article says rinsing removes "dusty stuff" from the filter (that suggests that there's off-tastes from the paper dust), and rinsing also helps reduce clogging of filter pores (presumably also from the "dusty stuff"). 

The quality of the paper filter certainly matters; comments and responses to this question support that. I buy the cheapest brown filters available, so I think it's unlikely that my filters "don't need rinsing" or so, but perhaps they're so cheap as to "not benefit from rinsing." This article suggests some filter taste-tests, so I did them and more. 

My experiments:


I poured water through rinsed and non-rinsed filters and tasted the water that went through the filter. Both taste faintly of paper, but I see no difference;
I have brewed simultaneous batches with rinsed and non-rinsed; I taste exactly no difference;
I have even gone so far as to chew on rinsed and non-rinsed paper filters to see if I could tell a difference. (Edit: to be clear, I chewed on these filters only to see if I taste a difference between rinsed and non-rinsed paper filters, not to somehow "condition" the filter before brewing use)


My conclusions:


Paper filters taste terrible -- mine anyway -- rinsed or not. I may have to revisit this question on brown versus white filters, buy better paper filters, or use a cloth-filtered Nel pot.
I wasted a lot of filters doing these tests.


In fact, after using a pre-rinsed filter I got a "structural failure" -- the bottom of the filter broke -- when brewing pour-over with a heavily rinsed filter. I'll probably have to eat some better-quality or white paper filters to make this fair.

In sum, my only conclusion is that quickly rinsing the inside and outside of the filter is the only way for this to have any benefit. I'm discounting any other benefit of pre-rinsing, such as rinsing with hot water would warm ceramic cone filter-holder or pot/mug.
Do you have maker with a removable filter basket? (Like the photo I attached below.) If so, then you might try what I've done:


removing the basket
placing the filter
then running water through it




The support of the basket protects against failures. And while you won't be able to rinse the reverse side easily, you will be able to get enough water into it to saturate through the paper. (Those flakes you mention will be trapped between the reverse of the filter and the basket.)

Hot versus Cold? I'd use warm. Some things you're removing may be more soluble at higher temperatures. I wouldn't go to the trouble of heating pre-filtered water. there is something to be said for water temperature affecting the filtering qualities of the paper by expanding the fibers, and in turn spaces between fibers. But without testing we'll have to assume it's a minor. If you only have cold filtered water, I suggest you use that. 

Why not hot water? First, a quick rinse of hot water isn't going to neutralize significantly more micro organisms that cold. You need boiling or much higher for a length of time to do that. Second, hot water will make the filter more prone to breaking.


  I have brewed simultaneous batches with rinsed and non-rinsed; I taste exactly no difference


This leads me to think that soaking is worth a try. If it works for rice to remove excess starch, it might work similarly with paper



A slightly different angle on this: 

Try to find the filters that don't need rinsing. When I filter I'm doing so to reduce the cholesterol raising impact of coffee. I prefer the taste of unfiltered coffee, but the evidence convinces me that filtered coffee is better for my cholesterol.

The study linked below, amongst others, shows that paper filters remove much of the cholesterol-raising compounds, as much as "80% of the lipid-solublue substance that was present..." Pre-wetting the paper --pre-loading the fibers with water, really-- seem as though it would reduce this absorbent property, although I can't back that up.

The hypercholesterolaemic factor in boiled coffee is retained by a paper filter