2 coffee filters = weaker coffee than 1 filter, right?

All other things being equal, if one uses 2 filters instead of just one when making coffee (automatic drip), this will result in weaker coffee because more of the coffee particulates are filtered out, right?

My coworker disagrees, he thinks that with two filters, the water moves slower, and hence will take more from the grinds, from being in contact longer with them, resulting in stronger coffee.

It seems that when he makes the coffee it tastes weaker, but this might be subjective.

This doesn’t seem like a difficult thing to test, but I’ve never tried it.
Are you sure your coworker isn’t making it weaker with just less ground coffee?

Just thinking about it, I’d have to agree with you, but I don’t have any physics to back you up.

OTOH, measuring spoon + 3 filters = blind taste test.

Nope, you’re coworker is right. That is, assuming that coffee grounds act like all other plant matter in the world that I’ve ever tinctured by the percolation* method. Thicker or layered cloth or harder packed marc (plant stuff) slows down the percolation, or the “drip”, which means the solvent (water) has prolonged contact with the marc, and extracts more constituents from it.

In the case of coffee, this means not only “stronger” as most of us think of it, but more bitter, as the bitter alkaloids take longer to dissolve. A regular packed coffee maker is carefully calibrated to remove just the right amount of bitter - slow down the process and it gets too bitter for most people’s taste.

*The percolation method of tincture making doesn’t mean the same thing as percolating coffee. Rather, it means packing plant matter into a cone of paper (often we use coffee filters for this) and pouring water/alcohol on top of it and letting it slowly drip through over a period of roughly 24-48 hours. The resulting liquid is as chemically strong as a traditionally prepared tincture involving simply soaking the herb in the same mixture for a month. The movement of the solvent through the herb speeds up the process considerably.

Guess that would depend on whether coffee’s taste depends on minute particles in suspension where the size of the particles is > the size of the filter, or whether it depends on various aromatic compounds in solution. I’m inclined to go with your coworker on this one.

I knew a guy who used your coworker’s method for the express purpose of making the coffee stronger. Proof? No.

Next time he makes coffee with two filters, after the brewing is done, separate the two filters and see if there is any significant amount of particulates trapped by the bottom filter. I’ll be surprised if there is.

On preview looks like **WhyNot ** has an authoritative answer.

The ‘particles’ which give coffee its flavor are too small to be filtered out.
I think what happens when you use two filters is that the water builds up on top of the grounds, and has a longer cooling time before passing through the grounds. Cooler water isn’t as efficient at extracting flavors, so you get weaker coffee.
When you use three filters, the flow rate is so slow that the water overflows the top of the filter. That gives you weak ‘chunky style’ coffee, with lots of ground up bean bits in your cup.

I have empirical evidence. :wink:

A few years ago I worked with a woman who insisted on using two filters. (Sometimes she actually used three.) She said it made the coffee ‘smoother’. The coffee grounds were measured by the dispenser. The coffee that used two filters was definitely weaker than the coffee made with one filter. Sex in a canoe.

I hate to disagree with Why Not but the coffee was not only weaker to my taste, but also to the taste of others in the office.

Maybe you can get a six dollar hydrometer from a homebrewing supply shop and measure the specific gravity of each coffee. I’ve got one but don’t drink coffee.
(Actually, I think I’ve got two - I’ll check when I get home from work. If so I can send you one).

Of course specific gravity isn’t going to tell you anything about caffeine content, acidity, bitterness, etc.

I would expect the effect of double filters to be less oils and less suspended solids, so it might have a weaker taste. But I would expect it to be more acidic and more caffeinated, so it would be “stronger” in that sense.

The coffee pot we use at my office has a “strength adjustment” to make stronger/weaker brew. It takes longer to make a pot when set to the “stronger” end of the scale. FWIW.

On a Mr. Coffee machine I had, accidentally using 2 filters caused the basket to overflow. It hasn’t happened with my Queasy Nart yet, so I don’t know about its flow rate. Different filter styles, too.

Those who favor the gold foil filter basket claim the paper filter removes the aromatic oils. It’s possible that double filters would give you even less aroma from your coffee.

I’d have to go with WhyNot on this one.
The only thing a coffee filter does is keeps the grounds out of your coffee and controls the speed at which the hot water passes through. Pass it through slower and you get stronger coffee.

If a filter actually made coffee weaker then in theory you could pour yourself a cup of weaker coffee by pouring it through a filter first. I don’t believe this to be the case.

Hampshire: Nevertheless the coffee I made reference to was noticeably lighter and tasted much weaker vs. coffee made with only one filter. Same amount of coffee grounds, same Bunn coffee machine.

Yup: Brew Temperature. If the coffee pot spits out really hot water, and the grounds holder is a good insulator, you might get stronger coffee by using two filters. It probably varies from machine to machine, but my experience is that two filters always gives weaker coffee. Sticking in another filter messes with the time/temperature profile, and hence the extraction kinetics.

Whenever I’ve used two filters, usually unnoticed until the problem shows up, the machine overflows and makes a huge mess. Apparently, in normal operation the water comes in faster than it goes out, so the water will rise to cover the grounds. In a delicate balance that won’t normally overflow. But the second filter slows the draining too much and the grounds cup can’t hold it all.
The same problem happens when you run out of filters and try to substitute a paper towel.

As do I. :wink:

I like strong coffee. In order to make it strong and not go through as much, I used to always use 2 filters - the coffee percolated through the grounds much more slowly, and I got my strong coffee.

Regardless of the coffee’s strength, using a second filter will remove particulates from the brewed coffee. This is a good thing, from what I’ve read (a quick Google search found nothing, however). Gold mesh filters let through a LOT of particles, in my experience.

If the coffee maker is automatic, it adds water to the filter assembly at a constant rate independent of the water level in the filters. So, residence time won’t change much, but the water level in the filters will be higher with more filters, I think.

In a very unscientific test, my coworker flipped a coin, and based on that result used two filters without telling me. I correctly guessed that he used two filters. I know this doesn’t mean much, just FYI.

It might be only a bitterness aftertaste component of the flavor that is weaker with the two filters.