When talking about filters, there are typically five main material types that are used: paper, metal, plastic, cloth, and glass. These filters can be applied in different shapes based on the machine or medium you’re using for coffee production. They all affect the final body and aroma of the coffee.
The Five Types of Coffee Filter Material
1. Paper Filters (Pour Over, Chemex, Aeropress, V60, Bee Hive)
Paper filters are the most common material used for filtering coffee. They work by removing most particulates from the final brew. They also tend to absorb some of the oils and aromatics from the coffee.
Bleached (White) vs Unbleached (Brown) Paper Filters
Paper filters can be broken down further into bleached and natural varieties. Paper is naturally brown and is bleached white. If a filter is brown, there is a good chance it’s unbleached and natural.
The natural filters impart a taste similar to wet cardboard, especially if you opt for a cheaper brand. It’s best practice to first completely wet the filter and allow water to pass through. Then dump the filtered water. This gets rid of this initial cardboard taste.
Filters are also bleached with chlorine and oxygen. So if you buy a filter that’s white, it’s likely bleached. Though only a miniscule amount of bleach is used in this process and won’t leech into your coffee. Oxygen is seen as the more natural option and are usually more high quality.
Overall, brown filters are better for the environment as they are less processed.
How is Viscosity Affected?
Color of the filter plays a minor role in the impact of filtration. The main thing we need to determine is how fast or slow the water is flowing through the filter and the impact it has on the extraction of the coffee.
You can determine this easily by doing a dry run with water. The rate at which the water flows through the filter will give you a good idea of how much resistance the filter has. If the flow rate is slow then the filter has more resistance to the particles. This means that it likely is preventing oils from passing through into the carafe.
This testing also allows us to determine how coarse or fine the grind needs to be. If the flow rate is slow then the grind needs to be more coarse. This will allow for ample time for the water to interact with the coffee grinds before it’s filtered.
Body of the Cup
Body is the way the coffee feels in the mouth (texture or oiliness). Generally, the more translucent the filter is the more body the you’ll have. You can also look at it in terms of weight. The heavier the filter, the lighter body in the brew. The lighter the filter, the more body in the brew.
2. Metal Filters (Espresso, Moka Pot, Siphon, Styles of Aeropress, Percolators, French Press)
There are typically two styles of metal filters. The first uses holes or slits to filter the coffee. The second is a wire mesh that will trap particulates from passing through. Both are made of of materials like stainless steel in order to prevent a metallic taste from being imparted on the coffee.
Metal Slits or Holes
This filter type is usually integrated into the pot itself. They are common in Moka pots, percolators, and Neapolitan flip pots. This type of filter allows all the oils and aromatics through as well as some finer solids into the brew.
This filter works similarly to how your screen door prevents bugs from getting in. The difference is that the filter is much finer and will trap most of the particulates. This type of filter is common in French Presses.
3. Cloth Filters (Siphon Brewers, Vacuums, Drip)
Cloth filters aren’t very popular these days, especially in the western part of the world. They work in a similar manner to a paper filter but they are able to be cleaned and re-used.
The cloth filter will offer some oils but not nearly as many as a metal filter can. As you can imagine, cloth based filters nature is to absorb anything they come into contact with. They are sort of a middle ground between paper and metal in terms of body and aromatic properties that can shine through. The amount of body highly depends on the type of material the cloth is made.
It’s important to note that these filters can stain quite easily. They need to be cleaned thoroughly to prevent the older oils and sediments from transferring into newer brews.
4. Plastic Filters (Cheap drip machines and french presses)
Plastic filters are often found in cheaply made drip brew machines. They can either be permanent or nylon mesh. Often these types of filters don’t last long. The number of websites that offer replacement “permanent” filters for these machines confirms this sentiment.
They are also noted for imparting unpleasant taste to the coffee. I’ve seen far less complaints of nylon mesh filters though. These are usually found in budget friendly french presses as opposed to metal mesh.
5. Glass Filters (Siphon/Vacuum)
Glass is quite common with vacuum pots, especially Cona models. The filter is positioned in the downspout of the vacuum’s upper bowl. They look similar to something Harry Potter would wield if he was a coffee brewing wizard.
The result is a heavier bodied cup. The body is similar to what a metal filter would provide but it’s definitely not as clean as a paper filter.
However, cleanup is a breeze as the material is glass.
All of these filters serve the purpose of filtering coffee grounds from the final brew. All of them have their distinct advantages and disadvantages. Most people will be familiar with the paper option but the others are interesting to look at and see how they affect the body and aromatic properties of coffee.