What are the Benefits of Flannel Filter Coffee? Why Pour-Over Coffee Flannel Filter Methods Have Been Phased Out

The Coffee Oils Controversy

Recently, a customer was enjoying a cup of Mandheling coffee and remarked, "This Mandheling is so clean, and it lacks the crema. The mouthfeel is somewhat lacking." He then recalled the Mandheling he tasted during his travels in Japan, with its reflective layer of crema on the surface and such a rich mouthfeel...

Filter Materials and Coffee Oils

In reality, whether you can extract coffee oils has little to do with technique and is mainly related to the filtering material. Nowadays, pour-over coffee typically uses paper filters as the filtering medium. Paper filters have extremely strong filtering capabilities, able to remove all solid particles and most oils. Therefore, coffee brewed with paper filters comes out exceptionally clean.

If you want to retain coffee oils, you need materials with less filtering power, such as flannel or metal mesh. Due to the larger gaps in metal mesh, not only can oils pass through, but some fine coffee grounds can also pass through, which is why relatively few people prefer using metal mesh as a filtering material.

Flannel, on the other hand, has fiber gaps that are just right. Flannel is a type of fabric with one side being cotton and the other being fleece. The greatest characteristic of this filter cloth is that it can filter out all solid coffee grounds while allowing coffee oils to pass through. Therefore, brewing coffee with a flannel filter can effectively preserve the coffee's oils. This layer of coffee oils makes the coffee smoother, fuller, and more mellow in the mouth.

The History of Flannel Filtering

The use of flannel for filtering coffee dates back to 18th century Europe. At that time, boiled coffee was popular, which involved putting coffee grounds into a pot and boiling them with water. After brewing, flannel filter cloth was used to strain out the grounds. Later, with the emergence of pour-over coffee, this method was introduced to Japan.

The Japanese discovered that using flannel, compared to the paper filters available at the time, produced cleaner coffee with a richer mouthfeel. Additionally, it could be cleaned and reused, making the cost per cup lower. At one time, flannel coffee was popular throughout East Asia. Even today, many coffee shops in Japan still insist on using flannel for their coffee. Nowadays, flannel has been almost entirely replaced by paper filters, and very few coffee shops use flannel to brew coffee, which brings us to the limitations of flannel.

Flannel's Limitations with Light Roasts

Flannel is not very suitable for brewing light roast coffee. Compared to paper filters, flannel's gaps are much larger, so its flow rate is significantly faster than paper filters. Furthermore, flannel filter cloth allows coffee liquid to pass through from all sides, meaning that when the water level is higher, the flow rate becomes even faster.

Therefore, baristas who use flannel to brew coffee typically use a full dose of coffee grounds, first moistening them with drops or a small stream of water, then pouring with a small stream of water in the center circle to avoid water flowing away from the sides.

The biggest difference between paper filters and flannel is that paper filters allow water to remain longer, creating an immersion extraction. Flannel, with its weaker water retention capacity, relies entirely on continuous filtration extraction. When brewing dark roast coffee, using a slow-paced, long extraction method can dissolve more complete flavors from the coffee, resulting in rich sweetness and bitterness.

When using flannel to brew light roast coffee, if you still use a slow-paced, long extraction method, the coffee extraction may be complete, but it will suppress the bright acidity of light roast coffee, creating heavy, thick flavors like black tea or brown sugar.

Even if you adjust the grind size to slow down the flow rate and use the same brewing method as with paper filters, the final flavor profile of the coffee will still lean toward tea-like, dull acidity, and poor clarity. In the wave of light roast coffee popularity, flannel's advantages are difficult to demonstrate, instead exposing its weaknesses.

Additional Challenges with Flannel

Different Brewing Techniques

Following the previous point, flannel brewing methods differ significantly from paper filter and cone brewing methods. To brew well with flannel, one generally needs to relearn and understand the proper use of flannel. Flannel brewing is quite experience-dependent and difficult to quantify with data. For most baristas who start with data-driven learning, this undoubtedly increases the learning curve.

Storage Difficulties

Although flannel filters are relatively expensive, they can be reused through proper storage. However, storing flannel properly is quite challenging. First, flannel cannot be dried, because the process of wetting and then drying will damage the fiber structure.

Therefore, after using a flannel filter cloth, it needs to be thoroughly cleaned, then placed in clean water, sealed, and refrigerated to prevent bacterial growth.

However, as the number of uses increases (typically starting from the third use), the filter will accumulate coffee stains, gradually turning yellow and darker. Consequently, issues with hygiene and flavor cross-contamination can easily arise in subsequent use.

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