Filters are generally made out of stainless steel, aluminum or paper (though coffee drinkers looking to add some bling to their kitchen can opt for a gold filter). The main difference between metal and paper filters is that the latter dramatically reduces the amount of small bits of ground of coffee, called fines, that end up in your cup. The more fines, the thicker the body or mouthfeel of the coffee. The fines also contribute some extra bitterness to the flavor, which is one of the reasons why French Press coffees often have more of a bite than an automatic coffee filter brew.
The paper filter also removes the oils contained within the coffee. When you order an espresso you may notice a few drops of oil on the top of your cup. Similarly, dark roasting coffee brings out these oils during the roasting process itself leading to an oily sheen on the beans (be careful though as that same oily sheen on medium roasted coffee is an indication of staleness!). Coffee oils contain flavor and aromatic compounds that improve taste. However, is it necessary for these oils to be present in your cup of coffee or does the brewing process extract all of the necessary compounds and infuse them in to the water directly? A quick google search did not yield any conclusive results, so we decided to do a taste test to find out.
We brewed two cups of coffee using the exact same ratio of coffee to water (our standard 16 grams to 170 mL with a two minute steep time) in our current brewing method of choice – the Aeropress. For the first cup, we used the standard paper filters that come with the Aeropress. In the second cup, we used our recently acquired stainless steel filter made by Able Brewing in the US.
The results? As expected, the body of the stainless filter coffee was much more pronounced compared to the paper filter, with a slightly syrupy mouthfeel. However, the stainless filter coffee was also a clear winner in the flavor category as well. While both coffees were excellent, the stainless filter reduced the acidity slightly while enhancing the chocolate flavors in the finish to make a rather striking cup. The paper filter coffee tasted almost too clean and balanced when compared side by side. While we can think of coffees where this balancing effect would be welcome, for this particular coffee – the pulp sun dried Arabica from Kalladavepura Estate – we preferred the boldness of the metal filter imparted in the cup.
Although we tested these filters using the Aeropress, filters used on coffee machines or any other brewing equipment similarly affect the taste of coffee. In fact, with equipments like coffee machines, you have a much wider variety of filters that you can opt for from bleached white or natural paper filters to cloth, steel and gold filters.