There are a variety of factors that go into making a great cup of coffee.
Which ones come to mind first?
Coffee? Water? Time? Temperature? Perhaps the brewing device?
One important factor probably gets less consideration than it deserves: the coffee filter.
Coffee filters are often considered no further than within the context of a specific brewing device. A Chemex uses a Chemex filter, a V60 uses a V60 filter, and so on – and that’s that.
Beyond simply separating the ground coffee material from the brew, the particular attributes of a coffee filter have a huge impact on the sensory experience of a brewed coffee beverage, from the color to the mouthfeel, to the balance of sweetness and acidity. This is because the design, material, and shape of your filter are determining what is and is not making it into your final brew.
In some ways, our coffee filters are the gatekeepers of tasty flavors.
If you like tasty flavors too and you brew coffee at home using coffee filters – listen up.
May we present: the KLLR Coffee Guide to Coffee Filters.
First thing’s first, what is a coffee filter?
A coffee filter is a device used for separating ground coffee material from the liquid coffee brew.
Most filters are made to fit a particular type of brewing device – i.e., made to fit the brew-baskets for specific automated brewing equipment, or designed to be compatible with particular pour-over drippers.
Choosing the appropriate type and size of filter is critical for brewing coffee properly.
Similar to how pour-over drippers are constructed out of a variety of materials, so are coffee filters. The most common materials coffee filters are made out of are paper, metal, and cloth.
How do these different materials affect the functionality of filtering coffee?
Paper filters hit the scene around the turn of the 20th century when Melitta Bentz, a housewife from Dresden, Germany, got fed up with constantly dealing with coffee grounds in her morning cup.
In desperation, she attempted using a variety of materials to filter the grounds from the brew.
Ultimately, she cut a piece from her son’s blotter paper, shaped it over her brewer, and – eureka! – the paper filter came to be.
On July 8, 1908, the paper coffee filter and accompanying brew cone were patented as a “Filter Top Device lined with Filter Paper.”
Today, paper coffee filters are the most commonly available type of coffee filter, available at essentially any grocery store and even many gas stations and are used for both automated brewing equipment and manual pour-over brewing applications.
To Bleach or Not to Bleach
The great debate within coffee filers is whether bleached or unbleached filters are preferable.
Many filter brands feature both (Melitta, for example, offers their filters in bleached, natural brown, and bamboo).
When thinking of paper, many of us picture white paper, such as printer paper or perhaps notebook paper. The fact is, whether a coffee filter or the page of a notebook, paper is naturally brown and most of it is subsequently bleached white using either chlorine or oxygen-based processes.
Bleached filters are often recommended and often the choice of cafes thanks to the fact that they contribute substantially less “paper” flavor to the brew. Oftentimes with some brown, or natural, filters – even with a rinse - the brew ends up featuring a paper flavor as a result of paper particulates from the filter media passing into the brew.
That said, natural filters had their own edge in that they are more environmentally friendly.
A 2012 study published in “Environmental Engineering and Management Journal,” found that discharge from chlorine-bleaching was “the most significant environmental issue” in pulp and paper mills.
Oxygen-bleaching, in contrast, requires less processing and, as a result, is better for the environment.
Most major filter manufacturers list what method of bleaching was used for their filters on the packaging.
Whether bleached or natural, it is advised to give your paper filters a rinse with hot brewing water before brewing your coffee.
This serves two purposes in that 1) it rinses the filter, reducing the likelihood of paper flavor and 2) it pre-heats your brewing device, reducing the amount of heat it may absorb from your brew slurry.
Steps to Rinsing a Paper Coffee Filter
- Position filter in brewing device as if ready to brew.
- Thoroughly rinse filter with hot brewing water until fully saturated.
- Discard rinse water.
- Dose your coffee and begin to brew!
Note: Not all paper filters are created equally. A high-quality natural filter may contribute less paper flavor to your brew than a low-quality bleached filter.
If, after rinsing, you still taste paper in your brew, try rinsing twice. If you rinse twice and still taste paper: try a different brand of filter.
Fun Fact: Paper filters can be composed right along with your coffee grounds. They decompose relatively quickly, especially when buried within the grounds rather than left at the top to dry out.
Paper filters can come in different shapes to accommodate different styles of brewing equipment.
The two most common shapes are flat-bottomed filters with accordioned edges, and cone shaped filters.
Flat-Bottom Filters are designed with the theory that a bed of coffee that is more even in depth will allow for roughly equal quantities of water to evenly pass through all of the grounds, thus, extracting more evening.
Most flat-bottomed brewing devices drain through several small holes at a relatively slow rate and require a coarser grind than many conical brewers.
Cone shaped brewers are designed with the idea that as brewing water passes down through the bed of coffee, it increasingly contains more content as it flows downward, or a decreasing concentration gradient (the difference in concentration of coffee compounds within the grounds vs. within the brew water), thus causing the water to extract less from coffee grounds lower in the bed. The cone shape ensures that more water flows through the coffee toward the bottom of the cone than toward the top to compensate for this change in concentration gradient.
Neither of these designs is inherently better or worse. Like many things in coffee, it ultimately comes down to preference.
What is known, however, is that the difference between these two design styles is perceptible in brewed coffee.
Sensory scientists at UC Davis Coffee Center recently partnered with Breville, whose Precision Brewer is capable of brewing with either a cone shaped or flat-bottomed filter basket and filter and found that their panel of professional tasters were able to taste distinct differences in coffees brewed with cone shaped baskets vs. flat bottomed ones.
Researchers understand that changes in filter shape will influence the way that water flows through the coffee grounds, thus, affecting how the coffee compounds are extracted from the coffee grounds and manipulated by the brew water. The details of this process, however, and how they lead to these impacts in flavor, are still being investigated.
Brewer-Specific Paper Filters
Many brewing devices have their own proprietary filters that they are intended to be paired with (with most having off-brand substitutions as well). These filters are often quite different from one another and can lead to additional differences in the characteristics between different brew methods.
Let’s use Chemex filters vs. Hario V60 filters as an example.
Filters for the Chemex brewer are cone shaped. They are up to 30% heavier than other brands. This means that they remove much finer ground coffee particles and more fats and oils than many other paper filters on the market.
This is why the Chemex produces a particularly clean cup.
Hario V60 filters are also cone shaped. They’ve been known to be on the thinner side, resulting in a more full body than some other paper-filtered brews. More recently, these filters have changed, becoming slightly thicker and reducing the body that so many have come to appreciate from V60 brews.
There are off-brand filters that will more closely replicate the old profile.
When shopping for filters, you may notice that many of them come in different sizes. These filter sizes correspond to the various sizes the pour-over drippers are offered in.
Be sure to know the size of your pour-over dripper when selecting filters.
Paper filters are the most prominent filters you’ll likely encounter so they got the lion’s share of this blog, but they aren’t the only type of coffee filter out there.
The best-known metal filters can be found in French presses and espresso portafilters (we often think of espresso as unfiltered but think about it, a portafilter basket really meets all the qualifications of a filter) but metal filters are available for the Aeropress, Chemex, and a wide variety of automated brewers.
Brews made using metal filters will feature a totally different cup profile than those created using paper filters. Metal filters have larger pores and therefore do not block as much of the coffee’s fats, oils, and ultra-fine ground coffee particles.
Maybe people that prefer their coffee “strong” prefer metal filters because of the resulting heavy mouthfeel that they can provide.
Metal filters, unlike paper filters, can be used over and over again, however, they do need to be cleaned with care. Immediately after each brew, they should be rinsed free of grounds, thoroughly rinsed and dried. Once a week, clean the filter, French press, etc. with a coffee cleaner such as Urnex Cafiza.
Perhaps the world’s oldest method of filtering brewed coffee is filtering with cloth. Like paper, cloth filters are very effective at keeping your brew free of grounds but similar to a metal filter, they let through more of the remaining fats and oils and so have a heavier body than you may expect from coffee brewed using a paper filter.
Cloth filters, like metal filters, can be used multiple times, although, they do have limits (after a couple dozen brews, they may begin to contribute unwanted flavors to your brew, but they can be used safely for much longer), and they require much more care. Between each brew, cloth filters must be thoroughly cleaned with brew-temperature water and then, if used frequently, the filters should be kept wet while storing for best results (i.e., a mason jar of water with several drops of bleach – rinse thoroughly before using).
Try Them All!
Like most aspects of brewing coffee, the best way to really learn the differences between the different types of coffee filters discussed in this blog is to try them for yourself. If you have the opportunity, try a variety of the different filters available for your favorite brewing methods and see how it changes the characteristics of your brews to determine what you like best!