So you have experimented with your brewer, grinder, water, beans, kettle, recipes, maybe a scale - now filters? As if there were not enough pieces to the home barista puzzle already. But bear with me. Unlike photo filters that change the outer appearance but don’t alter anything real, coffee filters are designed to impact the essence in your cup.
How much? In ten+ years of operating a Slow Bar, we’ve worked with pretty much all filters known to man. Here's some learnings.
A bit of history: The main motivation for filter invention is obvious: no one truly enjoys gritty grounds between their teeth. So in 1908 a practical woman by the name of Melitta Bentz decided to look for something that would decrease the amount of grounds in her cup. Like many great inventions, filters started with a simple, personal problem. There had been experiments with punctured metal cylinders before Melitta’s time, so she started with that - but her spark of genius was the thought of adding an extra paper layer.
The Melitta Filter went on to conquer the world of coffee. It’s a global brand today, and still owned by the same family in Dresden, Germany.
Today, the global coffee filter industry is growing by about 5% year over year. Revenue has grown from roughly $480 million to $600 million between 2018 and 2023. The two biggest markets are North America and Europe.
In the 107 years since its inception, filter design has evolved. In recent years mostly throughout the gadget driven world of specialty coffee. We see filter types supporting what we know about extraction, and based on different brewer shapes, sizes and materials.
What A Filter Influences
How much coffee oil can pass into the cup (it contributes to mouthfeel)
How many fines are passed into the cup (they contribute to texture)
How fast water moves through the filter (in combination with the brewer design)
Main Differences Between Filters
Material
Paper from Wood Fiber
Abaca / Hemp Fiber
Upcycled materials (Coffee grounds)
Bamboo
Ceramic
Metal
Cloth / Fabric
Resin / Plastic
Paper filters made from wood fiber are the most used due to their convenience. As far as flavor goes, a paper filter gives you the most options to experiment. However, reusable filters are becoming more popular, which is great news since it's supporting new innovations that combine sustainability and useability.
I will write about reusable filter materials in more depth in a future post.
For this one we focus on traditional wood fiber paper, Bamboo and Abaca (a fiber harvested from hemp). Abaca has gained popularity with companies producing specialty coffee filters. Depending on the source, Abaca can be a sustainable material. It also provides a specific texture that helps direct and speed up water flow. You can see this reflected in the price of these filters; Abaca and other plant cellulose filters run about $0.40 pp versus $0.10 pp for regular wood fiber paper.
Design
Size
Shape
Thickness
Porosity
Finish / coating
For brewers like Chemex or Orea, filter size and shape are specifically designed for the brewer and you will have little luck fitting those into different brewers.
However, most other cone shaped filters come in three basic sizes: 1 - 2 cup, 2 - 4 cup and 1 - 4 cup (Hario), which makes them versatile. Larger ones are available, mostly for automatic drip coffee machines, like 6 - 10 cups Melitta options.
This vague range from the manufacturers side is on purpose, because cup sizes differ from market to market. Most manufacturers calculate with a cup size of 8 ounces (180g/ml), which reflects more the European and Specialty Coffee standard.
Nevertheless, the biggest brands that sell pour over filters (see list below) fit different brewers. The only difference lies in how high the paper reaches.
If you often switch between making one cup for yourself and two+ for others, or you usually drink larger cups, going with a 2 - 4 cup filter will work for all of it.
Shape
The most common filter shapes are Cone round (pointed tip), Flat-Bottom or Basket, and Cone with a flat bottom (think classic Melitta). Lesser used shapes are Foldable Sheets and Disks. They all were originally designed for particular brewers and machines. The more brewers hit market, the more confusing the filter situation becomes.
But - if you have a cone shaped brewer, or one with a flat round bottom, you have flavor and filter flexibility.
Thickness
Here is where it gets interesting for extraction! There are no two identical paper filters on the market as far as thickness and porosity goes.
Thickness ranges from 120 μm for an Aeropress disk filter to 242 μm for a Hario tabbless filter (see table below). μm stands for micron or micrometer. For comparison, a human hair is about 100 μm thick.
The total paper thickness impacts how easily water travels through the filter and how much coffee oil stays behind, versus making it into your cup. The thicker your filter paper, the less body your coffee will have (oils add mouthfeel). Thicker paper can however produce a nicely balanced cup due to the reduced speed with which the water travels through (= longer brew time).
The thinner your filter paper is, the faster water can travel and the more oils make it into the cup. There is no good or bad in this, it all comes down to what kind of coffee you like (see quick brew chart below).
Thickness Examples
Porosity
In coffee, there are many pieces that act together to create the whole taste experience. Filter thickness and porosity are such a pair.
Think of thickness as blinders and porosity as the space in between. Depending on how wide you open the blinds more or less light comes in.
To produce a filter, individual strands of material are more or less tightly knitted together. The way in which they are arranged (i.e. straight, crisscrossed or random) creates thinner areas in between. The distribution and number of these “voids” creates the structure and overall porosity of the filter.
The individual strands a filter is made of range from 10 - 20 μm for paper. These pores are small enough to keep grit in the filter, but large enough for flavor, caffeine molecules and other compounds to pass through.
The larger the pores the more oil and fines pass into your cup. Cloth filters are an example of this, where individual strands can be up to 100 μm. These types of filters are woven, not pressed, so that porosity is overall much higher.
For paper, the thicker and less porous, the more tea-like your coffee becomes.
A good example here is the Chemex filter.
The paper is thicker than writing paper, with only slightly higher porosity.
This, in combination with the no-bypass design of the Chemex, makes brews more delicate. It also means that elegant floral, fruity and subtle sweet notes shine.
The filter paper and its very narrow cone shape tend to add to the overall brew time by restricting water flow. To balance flavor, texture and depth in a Chemex you need to adjust technique and grind size. But overall, a thick paper filter with low porosity makes sense when you are into complex, washed coffees that don’t play well with cream or sugar.
Porosity Examples
Finish: Crepe versus Smooth
Many widely available cone or flat bottom filters on the market have a medium thickness and porosity that lend themselves to popular devices like V60 or Kalita Wave, as well as middle of the road coffees.
But here is one more factor I want to mention for those who want to go deeper down the rabbit hole: how a filter is finished, or coated.
A filter can have full or partial porosity. Partial means that one side of the filter is smooth, holding more oils back, whereas the other side is structured (good for medium roasts). Full means that the filter is fully porous and waterflow is encouraged (good for smooth darker roasts).
A third version are filters that have full porosity only on top and are half porous towards the bottom (getting a bit nerdy here). This creates an effect where small fines that would normally float and get into your cup, are being drawn to the porous (crepe-y) sides of the filter, getting trapped, while keeping a medium amount of oils in the grounds. The result is a smoother cup.
Companies that specialize in filter design (see list below) usually offer in-depth information about finishes on their websites.
Special Features
Coating and special structuring are admittedly a bit “out there” for the normal coffee lover. But it can’t be denied that specialized patterns and structures, designed to work with one particular brewer, can indeed have a measurable positive effect on extraction. Sibarist is one example of a company celebrating the science of filters. Their products are designed and use materials that promote a specific water bypass and flow rate.
Which Filter Type Works Well For Which Coffee?
High thickness / Low Porosity / Smooth Finish:
Light Roasts
Washed Coffees
Co-fermented Coffees (added fruits/pulp during processing to create new flavor profiles and add fruit aroma)
Carbonic maceration (coffee cherries fermented in carbon-dioxide rich tanks during processing, creating a boozy or wine-y character)
In short, coffees that are delicate and floral, complex, and sweet.
Thicker filters also help reduce the often overpowering boozy-ness in highly fermented coffees without taking the interesting notes away.
Medium thickness / Medium to low Porosity / Partly coated Filters:
Medium roasts
Natural processed Coffees
Honey processed Coffees
Washed Coffees with sweetness and nut - caramel forward profiles
In short: Middle of the road, solid and smooth coffees that are naturally sweet, or processed that way. Medium to low acidity and flavors like plum or dark cherry, versus bright citrus.
Low to medium thickness / Medium to High Porosity / Fully Porous:
Darker roasts
All processes, minus carbonic maceration
Robust flavor types
In short: Medium-dark to dark roasted coffees with a smooth finish and full body, as well as deep flavors like dark chocolate, burnt caramel or molasses and dried fruits. These coffees benefit from a good, even and slightly faster flow rate in order for body and sweetness to develop, while keeping bitters at bay.
Good to know when you select a filter for your brewer:
You will more easily find information on paper thickness than on porosity. This is because thickness can be expressed in microns, no matter what type of filter you choose. Porosity on the other hand describes the percentage of space (pores) within the paper structure of the filter. This falls usually between 70 - 80%. The differences in design, material and manufacturing are vast. So even though porosity can be measured in various ways this is most often done in labs.
For end consumers, porosity is usually expressed as low, medium or high, rather than by a fixed number. To not overcomplicate, it is easiest to go by thickness when you start and simply feel the paper. That way you can spot differences in coating and roughness.
Filter types based on Thickness:
Low Thickness:
Aeropress: 120 ± 22 μm
Cafec: 150 ± 21 μm
Chemex unbleached: 167 ± 23 μm
Medium Thickness:
Hario unbleached: 203 ± 21 μm
Hario tabbed: 206 ± 21 μm
Cafec: 207 ± 21 μm
High Thickness:
Chemex bleached: 210 ± 22 μm
Hario tabbless: 242 ± 22 μm
Cafec*: 220 & 280 ± 21 μm
*Note: If you visit Cafec's website, they use the term density instead of porosity. The words have opposite meanings, but describe the same state. High porosity in this article spells low density on their site.
Easy ways to experiment:
Brew the same coffee with different filters
Brew a cup with two of the same filters layered on top of each other
Cut the bottom half of a filter off and create a double layer just for the lower part of the filter
Note the differences in brew time and flavor!
Where we go from here:
The way we process, roast and drink coffee has changed dramatically over the past decades, and it differs from country to country.
One future focus that most can agree upon is on producing less waste, and figuring out how to brew altered and completely new varieties of coffee, as climate and other environmental conditions change.
My expectation is that filters, brewing methods and techniques will keep adapting according to new flavor profiles and levels of quality. Lot’s of testing ground ahead!
For more resources on manufacturers and supplier lists etc. please consider joining our community Newsletter below where we share all things specialty coffee in more depth!