Why/how does filter paper block/trap coffee oils?

In summary, paper filters block cafestol and kahweol, which are both functionalized polycyclic molecules. These molecules have a molar mass around 315, which makes them too large to pass through a cloth filter. However, oil and water are two liquids that are immiscible, so they will not mix together. This prevents the cafestol and kahweol from getting into the brewed coffee.
  • #1
The Bill
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TL;DR Summary
What is it about filter paper that keeps coffee oils out of the brewed coffee?
What mechanism or mechanisms cause filter paper to block coffee oils? As I understand it, these "oils" are mostly cafestol and kahweol, which are both functionalized polycyclic molecules with a molar mass around 315.

Cloth filters do not prevent these oils from getting into the brewed coffee, at least not nearly as much.
 
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  • #2
I think that the primary purpose of the filters is obviously to block the grounds while passing the coffee, but then again, I'm not a very sophisticated coffe drinker (albeit an avid one).
 
  • #3
Filters for lab use frequently have recommended uses, in part based upon what can go through the filter with minimal binding to the filter material, regardless of their particle size.

You don't want to use a filter to filter your favorite protein through a filter that will bind proteins, for example.
It will remove your desired filtrate and more rapidly clog your filter.

The same considerations should apply to filtering coffee, but usually without the detailed scientific description of the filter's properties.
 
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  • #4
Well, the impression I get from listening to the specialty coffee community is that paper filtered coffee has much less of the coffee oils in it. Cloth filtered coffee has oils in it, as does metal filtered coffee like espresso and French press coffee.

I haven't yet seen mention of a type of paper filter for coffee that doesn't do anything to keep oils out of the final product.
 
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  • #5
It could just be a surface tension effect. The pores of a paper filter are usually much smaller than cloth. I know that oil filters will clog if water tries to pass.
 
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  • #6
My solution is to use a metal filter and never clean it. Once the equilibrium amount of oils has built up, oil adsorption is no longer a problem. BTW, I'm a single gentleman and we have been know to dispense with the formalities of cleaning.
 
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  • #7
I'm not looking for a workaround. I asked about the science of how this works the way it does with paper filters because that's what I want to know.
 
  • #8
Funny thing about filter paper. If it is wetted first with oil it will resist the water passing. If you wet it first with water it will resist the oil passing.
 
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  • #9
chemisttree said:
Funny thing about filter paper. If it is wetted first with oil it will resist the water passing. If you wet it first with water it will resist the oil passing.
Oil and water are two liquids that are immiscible – they will not mix together. Liquids tend to be immiscible when the force of attraction between the molecules of the same liquid is greater than the force of attraction between the two different liquids.

https://letstalkscience.ca/educational-resources/hands-on-activities/what-immiscibility

http://www.google.com/search?&q=immiscible

Cheers,
Tom
 
  • #10
Yes, that’s true Tom.
 
  • #11
chemisttree said:
Funny thing about filter paper. If it is wetted first with oil it will resist the water passing. If you wet it first with water it will resist the oil passing.
So, is there something other than "pore size" that makes filter paper so different from cloth in the way you're referring to here?
 
  • #12
I don’t believe so.
 
  • #13
chemisttree said:
I don’t believe so.
So, if you were to make a prediction based on your understanding: Given two filters of the same diameter used in the same design apparatus to filter the same sort of coffee, etc. etc.: Let's let it be given that the setup has one filter is made of cotton fabric and the other is made of the same type of paper fibers used in a common coffee filter paper, but with a large pore size between the fibers matching the pore size in the cotton filter.

Given all that, would you predict those two to have similar amounts of oils in the final product? Would you consider that to be a reasonable hypothesis, based on your experience?

I haven't worked with many of the filter media common in chem labs since the late 90s. I'm not personally familiar at all with any recent developments in lab grade filter media.
 
  • #14
Tom.G said:
Oil and water are two liquids that are immiscible – they will not mix together.
I promise I'll try to look this up tomorrow, but I believe in case of coffee if there are actual oils mixed in a fresh brew, then it's an emulsion.
Which may be an explanation for the efficiency of filtering too.
 
  • #15
The vast majority of the cafestol and kahweol recovered from a brew is found in the retained grounds. So it may simply be a matter of filtration efficiency being much higher in a paper filtered coffee. The brew methods that produce the highest amounts are unfiltered (e.g. Turkish). Metal filtered coffee (e.g. espresso) falls in between. The grounds themselves act as a filter but in the case of metal filtered coffees the hole size is still large enough to permit a significant amount of undissolved solids -- presumably containing lipids -- into the beverage.
 
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  • #16
The Bill said:
Summary:: What is it about filter paper that keeps coffee oils out of the brewed coffee?

What mechanism or mechanisms cause filter paper to block coffee oils? As I understand it, these "oils" are mostly cafestol and kahweol, which are both functionalized polycyclic molecules with a molar mass around 315.

Cloth filters do not prevent these oils from getting into the brewed coffee, at least not nearly as much.
I believe it is simply an issue of surface area. I’m assuming the paper filters have much more surface area and exponentially smaller pore size. The more delicate the material, the more it will absorb. I believe this is also the case with carbon block for water filters for example.
 
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  • #17
The Bill said:
As I understand it, these "oils" are mostly cafestol and kahweol, which are both functionalized polycyclic molecules with a molar mass around 315.
My understanding is that the largest component in the lipid fraction of brewed coffee is triglycerides.
 
  • #18
Depending on the kind of bean, either triglycerides or alcohol esters have the highest level within the lipid content. This is according to a NIH article.
 
  • #19
Also, keep in mind that the reason why cold brew tastes so good is because of two reasons. Hot water is not used because it is the heat which releases the oils from the grounds, and the oils are where the acid is concentrated. Secondly, after water is poured onto the grounds, the grounds are wrapped in cloth overnight to absorb even more oils. Then for the actual “brew”, tepid water is poured through the grounds for the last time. The result is a virtually oil free liquid, hence smooth tasting, acid reduced, cup of coffee.
 
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  • #21
I didn’t know that. Maybe it could be the ALCOHOL esters contributing to cirrhosis.
 
  • #22
The Bill said:
As I understand it, these "oils" are mostly cafestol and kahweol
The matters of 'coffee' seems to be very diverse, and it's really hard to dig through all the different approaches (beliefs, preferences, paywalls and even: instant coffee and biofuels ?:) ) but for me it seems that the mentioned 'oils' are just the ones accused for the most biological activity, and not the most frequent present by mass percentage.

Anyway, it seems to be a fact (fact, up to the worth of some googlework) that these 'oils' in a brew comes as emulsion, and that allows to take things a lot more focused, more industrial area: emulsions and filtering.

When it's about emulsions and filters, the effectiveness depends on the fibers: surface activity/affinity.

So, regarding the original question: if paper coffee filters are more effective than cloth filters then that's likely because their affinity for oils is higher.
As far as I could go it's hydrophobic and oleophilic what would be good keywords for more digging.

Hope that helps.
 
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  • #23
At brewing temperatures, both are solids. They melt at 370F. While they may dissolve in oils, they also have hydroxyl groups (along with substantial polynuclear rings) which may provide some water solubility. As such, the paper vs. cloth filter media have some differential effects partially due to the different mechanical efficiency of the selected filter media. Both cloth and paper filters can be manufactured in many ways, each having varying degrees of efficiencies. General statements may be made differentiating the two but it would take clear definitions to clarify efficiency.

Some considerations:
1) As solids, they are both subject to mechanical filtration.
2) As being relatively nonpolar, they will tend to be absorbed onto oils. With the oils bound into the filtered grounds, most of these will remain in the solid bulk.
3) Some will pass through the filter mechanically due to small particle size and the rest will pass through due to the small amount dissolved in the water.

Neither of these are acids. They are polyols with a cyclic ether.
https://en.wikipedia.org/wiki/Kahweol
 
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  • #24
rayj said:
At brewing temperatures, both are solids. They melt at 370F. While they may dissolve in oils, they also have hydroxyl groups (along with substantial polynuclear rings) which may provide some water solubility. As such, the paper vs. cloth filter media have some differential effects partially due to the different mechanical efficiency of the selected filter media. Both cloth and paper filters can be manufactured in many ways, each having varying degrees of efficiencies. General statements may be made differentiating the two but it would take clear definitions to clarify efficiency.

Some considerations:
1) As solids, they are both subject to mechanical filtration.
2) As being relatively nonpolar, they will tend to be absorbed onto oils. With the oils bound into the filtered grounds, most of these will remain in the solid bulk.
3) Some will pass through the filter mechanically due to small particle size and the rest will pass through due to the small amount dissolved in the water.

Neither of these are acids. They are polyols with a cyclic ether.
https://en.wikipedia.org/wiki/Kahweol
When you say “both” and “neither”, I’m not sure to what items you are referring. According to healthline.com, not only is coffee acidic, but it contains nine major acids. Additionally, from the literature available, it seems that these acids are concentrated in the oil.
 
  • #25
I'm curious if it's possible to make a paper filter for coffee that makes coffee that tastes like cloth filtered coffee. Preferably without the cost of materials and production going up by an astronomical amount.
 
  • #26
What material is the cloth filter made of? Cotton? Nylon? Aramid?
 
  • #27
The Bill said:
make a paper filter for coffee that makes coffee that tastes like cloth filtered coffee
I have a feeling that once you get that it'll be exactly like a cloth filtered coffee, without the benefits of the paper filtered stuff... But anyway, please keep in mind that it's not only about filtering, but about food-rated filtering.
 
  • #28
moriah said:
When you say “both” and “neither”, I’m not sure to what items you are referring. According to healthline.com, not only is coffee acidic, but it contains nine major acids. Additionally, from the literature available, it seems that these acids are concentrated in the oil.
moriah said:
When you say “both” and “neither”, I’m not sure to what items you are referring. According to healthline.com, not only is coffee acidic, but it contains nine major acids. Additionally, from the literature available, it seems that these acids are concentrated in the oil.
moriah
In item 1), "both" is the adjective of the phrase "As solids". Solids reference the initial statement of composition "cafestol and kahweol" as being oils.

Yes, healthline.com states that coffee is acidic. Consider the characteristics of acidic food items such as vinegar and lemons. Both are sour; sour is the commonality of acids.

The 'opposite' of sour is bitter which is a property of alkaloids such as caffeine. Depending upon the type of bean and the preparation method, there is 2 to 6 times as much caffeine as acids in coffee.
https://pubmed.ncbi.nlm.nih.gov/25014672/

Note that each molecule of caffeine has three centers of alkalinity, where the CGA in coffee has one. Chemically, we may expect coffee to tend to bitterness over sour.

While I do not drink coffee regularly, I find it bitter and not sour.

It is important to review several, independent sources of information and assess the differences to help determine the most likely representation of reality.

Coffee is complex. Filtering is complex. Show the relationships, assess what influences the property being questioned. Nothing is 'known' exactly. Everything is a likelihood. What is the most likely and it is still a guess, but a more informed guess.
 
  • #29
Try making cold brew with cheese cloth. After it is “brewed”, heat the liquid you’ve produced. Because coffee is too acidic for me, I find that even brewing the traditional way with hot water and paper filter, still yields too much acid for my taste. Anyway, because there is 24 hour process involved in cold brew, the cheesecloth absorbs a very large amount of the unwanted substances we’ve been discussing. Like anything worthwhile, it takes time to make.
 
  • #30
moriah said:
Try making cold brew with cheese cloth. After it is “brewed”, heat the liquid you’ve produced. Because coffee is too acidic for me, I find that even brewing the traditional way with hot water and paper filter, still yields too much acid for my taste. Anyway, because there is 24 hour process involved in cold brew, the cheesecloth absorbs a very large amount of the unwanted substances we’ve been discussing. Like anything worthwhile, it takes time to make.
 
  • #31
When you taste 'normal' brewed coffee, do you find either a sour or a bitter taste? How about for the cold brew?

If neither, how would you characterize the taste?
 
  • #32
Yes, most coffee has acidic flavor. Cold brew is what they use for iced coffee. It has a smooth, non-caustic taste. I would liken it to an espresso drink like a latte. There must be something in the way that Starbuck’s for instance, roasts it’s beans specifically for espresso. It’s much smoother than the drip coffee which is brewed in an urn.
 
  • #33
Rive said:
I have a feeling that once you get that it'll be exactly like a cloth filtered coffee, without the benefits of the paper filtered stuff... But anyway, please keep in mind that it's not only about filtering, but about food-rated filtering.
Yes, that's the exact point I'm working toward with this whole thread. I certainly wouldn't want to work with a filter material that has the properties I want on paper (lol) without being made with known food-safe materials and processes.

And the point is exactly that I'd like the ability to make coffee that tastes like and has the mouthfeel of cloth filtered with the same workflow as paper filtered.

It's not that I strictly prefer cloth filtered coffee over paper filtered, I like both for different reasons in different situations. And I'd like to be able to get the cloth filtered experience without the whole rigamarole of using my cloth filters.
moriah said:
Try making cold brew with cheese cloth. After it is “brewed”, heat the liquid you’ve produced. Because coffee is too acidic for me, I find that even brewing the traditional way with hot water and paper filter, still yields too much acid for my taste. Anyway, because there is 24 hour process involved in cold brew, the cheesecloth absorbs a very large amount of the unwanted substances we’ve been discussing. Like anything worthwhile, it takes time to make.

Cold brew is a whole different beast, to me. Warmed up or not. I'm not saying it's bad or that I don't like it, but it's an orthogonal option to the cloth/paper axis I'm about in this thread. If I do cold brew it'll be because of the ways in which it's uniquely different from other brewing methods.
 
  • #34
The Bill said:
Yes, that's the exact point I'm working toward with this whole thread. I certainly wouldn't want to work with a filter material that has the properties I want on paper (lol) without being made with known food-safe materials and processes.

And the point is exactly that I'd like the ability to make coffee that tastes like and has the mouthfeel of cloth filtered with the same workflow as paper filtered.

It's not that I strictly prefer cloth filtered coffee over paper filtered, I like both for different reasons in different situations. And I'd like to be able to get the cloth filtered experience without the whole rigamarole of using my cloth filters.

Cold brew is a whole different beast, to me. Warmed up or not. I'm not saying it's bad or that I don't like it, but it's an orthogonal option to the cloth/paper axis I'm about in this thread. If I do cold brew it'll be because of the ways in which it's uniquely different from other brewing methods.
The Bill said:
Yes, that's the exact point I'm working toward with this whole thread. I certainly wouldn't want to work with a filter material that has the properties I want on paper (lol) without being made with known food-safe materials and processes.

And the point is exactly that I'd like the ability to make coffee that tastes like and has the mouthfeel of cloth filtered with the same workflow as paper filtered.

It's not that I strictly prefer cloth filtered coffee over paper filtered, I like both for different reasons in different situations. And I'd like to be able to get the cloth filtered experience without the whole rigamarole of using my cloth filters.

Cold brew is a whole different beast, to me. Warmed up or not. I'm not saying it's bad or that I don't like it, but it's an orthogonal option to the cloth/paper axis I'm about in this thread. If I do cold brew it'll be because of the ways in which it's uniquely different from other
The Bill said:
Yes, that's the exact point I'm working toward with this whole thread. I certainly wouldn't want to work with a filter material that has the properties I want on paper (lol) without being made with known food-safe materials and processes.

And the point is exactly that I'd like the ability to make coffee that tastes like and has the mouthfeel of cloth filtered with the same workflow as paper filtered.

It's not that I strictly prefer cloth filtered coffee over paper filtered, I like both for different reasons in different situations. And I'd like to be able to get the cloth filtered experience without the whole rigamarole of using my cloth filters.

Cold brew is a whole different beast, to me. Warmed up or not. I'm not saying it's bad or that I don't like it, but it's an orthogonal option to the cloth/paper axis I'm about in this thread. If I do cold brew it'll be because of the ways in which it's uniquely different from other brewing methods.
If you like the taste of cloth filtered coffee, I can’t see how you can maintain that flavor while using another medium. The only solution I can figure is if you somehow tweek the process of brewing itself without changing the medium. Perhaps you can use several layers of cloth instead of one.
 
  • #35
You could always use no filter medium and completely remove that issue.
  1. Brew your coffee with the grounds suspended in a container of heated water for some period of time.
  2. Let the grounds settle out (or centrifuge them if you are in a hurry.
  3. Pour off the supernatant (the coffee), leaving the grounds behind in the original container.
  4. Enjoy.
 

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