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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:

  1. 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.
  2. 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.

5

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:

  1. removing the basket
  2. placing the filter
  3. then running water through it

removable mesh filter basket

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

3

Let's answer your first question first:

What's the best way to rinse a paper filter? Inside, outside, both? Soak? Hot or cold water?

You can't really rinse only the outside/inside of a paper filter. When you drop water on a piece of paper, it doesn't just stick onto the outside/inside, it soaks both sides of the paper filter. So, both sides. You probably want to soak your filter. This will get rid of any unnecessary chemicals and oils filtered from your filter. This will help make your coffee taste better. Your Serious Eats article is very accurate. Well, soaking in hot water should do. Hot water will might peal off some paper plus a lot of harmful stuff. It is one-kill wonder for bacteria. The hot water will burn your harmful bacteria to death. So answering your first question: Both, Yes, Hot Water

Now let's answer your second question:

How does it help?

Well, filters are needed to keep coffee clean by extracting and "keeping" the chemicals and oils. Then, what cleans the filters? This is where rinsing comes in. Let me show you an example. Your clothes keep you clean then you put them in the washing machine to get them clean. So the rinsing is just like the washing machine. Over time, the paper will absorb so many chemicals and oils, the performance goes down like a rock. Some trapped chemicals will join the coffee, allowing the coffee to be contaminated and less tasty. Rinsing will allow the hot water to kill the bacteria and let the filter transfer the chemicals to the water, where it will belong somewhere in a sewer. This will leave the filter very clean.

And now I will answer your bonus question (Do you award extra rep for this ;-)?):

What is being rinsed off?

Well, the chemicals and oils of course! As said in my previous answer, the water will take the chemicals and oils to the sewer with it. The pores in which the filter needs to cleanse are then empty and more useful. Paper sometimes peel off but will end in the sewer like the chemicals and the water. After one use, it is time for the trash. Of course, first-timers will have to learn that dust and other particles will also ruin the flavor and filter. That is really the "dusty stuff".

Bonus Information About Your Experiments:

Looks like they don't work. Sure, most coffee filters will add a papery taste to your coffee, depending on its quality. First, doing the first experiment doesn't really do anything. You need to add coffee, not water, to see a difference. An bad, uncleaned filter will add a papery taste plus some more unwanted taste into your coffee. A good, rinsed filter will add a tiny papery taste to your coffee. Adding something in which it has flavor will make the experiment more fun (a lot more coffee to taste) and effective. That also goes to your second experiment which almost is the first experiment itself for some reason... Anyways, chewing paper filters will absolutely not do anything. All that does is leave you complaining and spitting for the next 12 hours. You might need a mint and some mouthwash after that for personal hygiene reasons :-).

I hope this helps you!

  • 1
    Though the entire filter gets wet, I can rinse the outside only. Upon closer inspection, there are some loose paper flakes that come off from the inside and outside; rinsing only the outside would leave the paper flakes on the inside. Bacteria has nothing to do with this; the temperature and duration of this rinsing is nowhere near enough for real anti-germ action, and that's not the purpose of rinsing. I'm chewing the filters to see if it has a taste, not to condition the filter for use. Are you saying that chemicals and oils are being rinsed off of the filter? Do you have a reference? – hoc_age Feb 24 '15 at 12:15
  • @hoc_age, Uhhhh, lost the reference... – Anthony Pham Mar 31 '15 at 2:08
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I learned in a chemistry lab that a paper filter does not "work" i.e. "filter" if it is not wet. If you put a paper filter in the cone and wet it before putting the coffee in the filter works better as a filter. Do this little test - make coffee with a dry filter and shake out the grounds. You will notice the filter is discoloured and had absorbed some coffee. Wet the filter first and after making coffee shake out the grounds. The filter is not discoloured with coffee. The filter has "filtered the coffee" but it has not absorbed some of it in the process.

  • Interesting. You suggest that there a difference in filtering performance from pre-wetting the filter, versus the filter getting wet whilst brewing the coffee? – hoc_age Feb 10 '16 at 13:40
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    I was unable to duplicate the results you are suggesting. My filters look the same after brewing regardless of whether they were prewet or not. – Suspended User Feb 11 '16 at 0:26
  • The purpose of pre-wetting the filter is to allow liquid to more easily/quickly flow through it via capillary action. If you don't pre-wet the filter must first soak up coffee water before becoming saturated and THEN it will allow coffee to flow through. This can end up causing the liquid coffee to sit with the grounds too long. – meskarune Mar 28 '16 at 20:57

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