Some coffees clog the coffee filter -- Why or how?

In summary, the resident expert's wife has given up even refrigerating coffee, as the humidity is high enough for condensate to collect on the bean. The fine grind of African beans makes the brew time very long.
  • #1
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TL;DR Summary
Some coffee ground beans when brewing make the flow-through of the filter so slow, like the filter paper is being clogged. Usually this is with African origin coffees. I am curious as to why or how.
The summary describes the situation. Most coffee ground beans let the hot water go through the filter paper more or less slowly maybe taking a few minutes to brew a serving of coffee through the coffee filter paper. Some other beans, usually of African origin, take much longer to brew. The flow-through is more than just a few minutes - often more like 30 to 50 minutes to brew 9 or 10 fluid ounces of the brew, like the paper is clogged. The resulting brewed coffee are usually very good or excellent , but just that the brew time is so long. I am interested in how or why.

I felt like asking about this after the topic of posts in
Chemistry news on
  • #2
Here is what I know from personal experiment. You can't use a "blender" style electric coffee mill for espresso without clogging the filter. These grinders produce a large range of particle size and a fine grind will contain some hyperfine powder. Instead a burr grinder with carefully spaced counterrotating burrs are used to produce a uniform albeit very fine grind. The mixed size grind packs into the filter with the small and large particles clumpimg together in a mass just like aggregate in concrete: very strong and nearly waterproof. The uniform powder from the burr will form a puck that is porous like sintered metaland let the espresso through.
I would guess the African beans produce a similarly disadvantageous grind for you. Maybe it is the roast or the oil content?.
I take my coffee seriously.
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  • #3
The resident expert here, my wife, says:

"It must be ground too fine, I've never heard of that problem with African coffees. I often get beans from Ethiopia or Kenya and never had a problem."

She grinds them at time-of-use, very noisy!
  • #4
hutchpad and Tom G
Let me reemphasize, it is usually some AFRICAN coffees, which when ground and brewed seem to usually make the brew time very long.

For some additional practices, let me say I roast the beans myself; always do a light-roast; do the grinding the same way each time using one of the small typical electric coffee grinders that you can get from drug store, Target, Walmart, Albertsons, or typical common retail place. Nothing fancy about the grinder. Always do the grinding in the same machine; always a light roast level. Origins from South America, Central America, Indonesia, brew times in the range from about 10 to 20 minutes. Origins from Africa, brew times between 45 and 50 minutes or so.
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  • #5
My guess would be different cultivars may have beans that behave slightly differently during grinding (which doesn't make what @hutchphd wrote wrong - problem can be related to the combination of beans/grinder) - and I wouldn't be surprised if most of the Africa used other cultivars than the other parts of the world.

And Ethiopia and Kenya are definitely in Africa.
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  • #6
  • #7
Could be appropriate if you live in a desert.

Resident Expert (wife) has given up even refrigerating coffee. Being a few blocks from the Pacific Ocean, the humidity is high enough for condensate to collect on the bean... which makes cleaning the grinder more of a chore.

This is beginning to sound like asking people "How to boil an egg?"
Ask ten people and you will get 15 different answers!

(OK, I'll stop now.)
  • #8
1. Beans from Africa have a different size distribution after grinding than beans from elsewhere.
2. African beans’ grounds swell differently during brewing than beans from elsewhere.
3. African beans’ grounds have a different zeta potential during the brewing process that prevents or will supress particle aggregation. Particles remain finer and tend to block filters.

We need a laser scattering test to measure
1). Particle size distribution of the finest fraction(s)
2) how particles swell during brewing (another laser scattering experiment)
3) zeta potential of particles
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  • #9
Somehow, I expect the number of significant figures in the price of those machines approaches the number of particles coming out of the coffee grinder!

I think I would rather get a head start by rigging the alarm clock to start the coffee grinder while I'm waking up. :wink:
  • #10
Yeah, but if you had one at work…..
I sure miss my lab.
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  • #11
Tom.G said:
start the coffee grinder while I'm waking up

gmax137 said:
Years ago I worked with a guy from Sri Lanka. He had contempt for the coffee in the break room. Told me how his mother would wake up early to roast the bean and prepare "real coffee."
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  • #12
Not clear where the quote from gmax137 came from in post #11, but some people not only in Sri Lanka, have become aware of the advantages of roasting and brewing good quality coffee; especially for how the roasting and brewing can be controlled to give a very very good flavor of coffee beverage.
  • #13
symbolipoint said:
Not clear where the quote from gmax137 came from in post #11
I didn't know why I got an "Alert" for this thread, until I saw the Quote in #11. The quote is from the "How do you like your coffee thread. You can see where quotes come from by clicking on the little Up Arrow in the "Name said:" box

  • #14
Thanks for the information about the link to other quotes. I really never noticed that icon until you explained it. This is helpful, but...

Now hopefully back to the main topic.
  • #15
  • #16
Keith_McClary said:
So I might infer that many african coffees are dense, and grinding them (if light roasts) makes them shatter, and so produce much finer ground particles, therefore clogging the filter paper more?

Maybe too your description of the flavors are what I remember, but it's been a while. I've b een avoiding african coffees because of how long brewing takes. ( I will have to try again. )

Related to Some coffees clog the coffee filter -- Why or how?

1. Why do some coffees clog the coffee filter?

Some coffees have a finer grind or higher oil content, which can cause them to clog the coffee filter. This can also be due to the type of coffee beans used or the brewing method.

2. How can I prevent my coffee from clogging the filter?

To prevent your coffee from clogging the filter, you can try using a coarser grind, using a different type of coffee bean, or adjusting your brewing method. You can also try using a paper filter instead of a metal one.

3. Can the type of coffee maker affect clogging of the filter?

Yes, the type of coffee maker can affect the clogging of the filter. Some coffee makers have smaller filters or slower brewing methods, which can result in clogs more easily. French presses and pour-over methods are less likely to have clogging issues.

4. Is clogging of the filter harmful to my coffee maker?

Clogging of the filter can potentially harm your coffee maker if it causes the machine to overheat or if it leads to a buildup of residue. It is important to regularly clean and maintain your coffee maker to prevent any damage.

5. Can I reuse a clogged filter for my next cup of coffee?

It is not recommended to reuse a clogged filter for your next cup of coffee. The clog can affect the flavor and quality of your coffee, and it is also unhygienic to reuse a dirty filter. It is best to use a fresh filter for each cup of coffee.

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