Water as the Defining Variable in Coffee Filter Manufacturing
When manufacturing coffee filters—more precisely, when producing the paper used for filters—what is the most important factor?
The primary raw material, wood pulp, is of course important. Depending on the type of pulp, fiber length and strength vary, which in turn can influence the thickness of the filter paper and the number of effective pores within its structure. However, once one understands the actual papermaking process, a different conclusion emerges.
Beyond pulp, the single most critical factor determining paper quality is water.
In reality, the pulp used by most filter paper manufacturers is not particularly extraordinary. Marketing has often exaggerated the idea that certain “special fibers” inherently produce superior filters, but in practice, the difference is less dramatic than advertised. Water, on the other hand, plays a decisive role.
Theoretically, producing one ton of paper requires dozens of tons of water. Discarding such volumes after a single use would be highly inefficient, so water is recycled multiple times within the system. Naturally, with each cycle, the water becomes increasingly contaminated. It accumulates chemical residues, lignin degradation byproducts, hemicellulose, microorganisms, fatty acids, and numerous other dissolved or suspended substances. This process water—commonly referred to as “white water”—gradually turns cloudy and opaque.
As a result, the later stages of production may introduce undesirable odors into the paper itself. It is similar to doing laundry repeatedly without ever changing the wash water. Who would want to wear clothes cleaned in dirty water?
If a white paper coffee filter emits an odor, it is typically attributable to one of two sources: chemical residues or an earthy, musty note. The earthy smell is often associated with geosmin, a compound produced by microorganisms in contaminated water. By contrast, the natural “woody” scent of pulp is largely eliminated during the bleaching process. In fully bleached white pulp, a true wood aroma is unlikely to remain. What many people describe as a “paper smell” is, in fact, more accurately a combination of chemical treatment residues and the characteristic odor of the papermill’s process water.
The definition of a “good” filter ultimately depends on one’s priorities. Recently, I have come to believe that the ideal filter is one that reveals the pure character of the coffee without interference. A filter made from ordinary fibers but manufactured under strict water management protocols may produce a cleaner and more transparent cup than a filter marketed as premium fiber-based, yet produced under less rigorous water control.
In the end, water management may matter more than fiber prestige.