Easily identified by their porcelain white colour, bleached filter papers are made through adding small amounts of chlorine or put through the cleaner process of oxygen-bleaching to achieve this result. The reason for this process is to eliminate any impurities within the filter paper that may interrupt the coffee brewing process, with the goal of creating a consistent, great tasting filter coffee.
Despite some initial concern at their conception that bleached filter papers have negative health impacts on coffee drinkers, it has been proven that modern examples are perfectly safe for brewing. However, this does not make them safe for the environment, as studies have revealed that once discarded, bleached filter papers will not decompose in an efficient or eco-friendly way. By adding an additional step in the production process, the pollution output of factories producing filter papers is further increased.
By contrast, unbleached filter papers that are brown in colour, require far less processing and decompose at a much faster rate, reducing their environmental impact. The downside to their use is that the flavour of pour over coffee can become less consistent, and some tasters argue it gives a defective, papery tasting note.
The counter argument for this setback is that rinsing filter papers negates the papery flavour, along with the fact that bleached filter papers have been known to have the same effect.
Despite the difference between bleached and unbleached filter papers, there are a host of other factors that play a significant role in the resulting coffee. Considering thickness greatly alters flow rate, meaning that coffee can brew too quickly if the paper is too thin, or flavour-packed oils can be retained by the paper if too thick.
Fortunately, the difference in price of filter papers is minimal, meaning the purchasing decision comes down to personal preference; environmental conscience or results.