What is the principle behind magical filter paper? What are the characteristics of non-woven coffee filter paper? What is non-woven fabric?

Introduction to the Magical No-Bypass Filter Paper

Recently, a friend brought FrontStreet Coffee a special filter paper to review. He mentioned it was a magical no-bypass water filter paper that, before we started extracting coffee, would not allow any liquid to seep through regardless of what we poured into it. Only when coffee grounds were added and hot water came into contact with them, transforming into coffee liquid, would it begin to permeate through.

This immediately piqued FrontStreet Coffee's interest, so today we're going to test just how magical this filter paper truly is!

Examining the Special No-Bypass Filter Paper

From the packaging introduction, FrontStreet Coffee discovered that this is a non-woven filter paper, but both in appearance and texture, it differs significantly from conventional non-woven filter papers. As we all know, non-woven filter papers are made from special plastics. Because they don't require spinning and weaving processes, they also have the alternative name of "non-woven fabric." Since the gaps in non-woven filter papers are larger than those in regular wood pulp filter papers, not only coffee liquid but also coffee oils and fine particles can pass through, enhancing the aroma and body of the coffee. However, this also makes their texture relatively rough.

This special non-woven filter paper, however, looks much closer to wood pulp filter paper, and its texture isn't rough at all—on the contrary, it's quite smooth with a slight velvety feel. For details, see the image below: from left to right are wood pulp filter paper, the special non-woven filter paper, and conventional non-woven filter paper.

Testing the Filter Paper's Unique Properties

So FrontStreet Coffee began testing, placing the filter paper in the filter cup and pouring in room temperature water, hot water, and coffee liquid respectively.

The results showed that when pouring room temperature water, indeed no liquid could permeate through the filter paper. The water inside the filter paper behaved like oil in a non-stick pan, completely repelled. However, when FrontStreet Coffee later used hot water and coffee liquid, some liquid did permeate through the filter paper. Although the permeation speed was very slow, it wasn't completely repelled like when pouring room temperature water. FrontStreet Coffee then conducted extraction tests, beginning to brew coffee. As soon as the coffee grounds and hot water came into contact in the filter paper, coffee liquid immediately began to release, flowing out at a relatively fast speed—completely different from the flow rate when just pouring water.

After brewing finished, we could clearly see on the filter paper that only the parts that had contact with coffee grounds were wetted by coffee liquid. The parts above the coffee grounds, which hadn't been in direct contact, remained dry (even though water was intentionally poured over them during brewing). This demonstrates that this filter paper can indeed achieve bypass-free extraction (provided the coffee bed wall wasn't broken down).

The Science Behind the Magic: Lotus Leaf Biomimicry

This is indeed quite a magical tool, and its ability to perform this way is mainly attributed to the filter paper's special structural design—the lotus leaf biomimetic structure. As we all know, lotus leaves are hydrophobic because their surface is covered with many micro- and nano-scale particles, with air filling the gaps between particles, forming a nano-scale air film. At the same time, their surface is also covered with a waxy layer. It's the combination of these two factors that allows lotus leaves to remain untouched by water, with water droplets only able to roll on their surface. The filter paper is manufactured using the same principle, giving it the same hydrophobic properties.

However, this structure isn't invincible—if we use additional fine solids to intervene and polish it, disrupting its micro-nano structure, the hydrophobicity will be reduced. And the addition of coffee grounds can achieve this purpose! Through the combination of coffee grounds and water, the tumbling during brewing breaks down the filter paper's hydrophobicity, allowing coffee liquid to permeate through.

In addition, high humidity environments and high-acidity liquids can also break down this structure. That's why when we tested with hot water and coffee liquid above, some liquid permeated through the filter paper. However, their "destructive power" wasn't as strong, so the permeation speed was very slow.

Alright! Now, FrontStreet Coffee will explore the differences in coffee brewed with this filter paper compared to regular filter paper and conventional non-woven filter paper, as well as their flow rates!

Brewing Experiment and Results

In this session, FrontStreet Coffee will brew three pots of coffee, using regular wood pulp filter paper, non-woven filter paper, and this special non-woven filter paper respectively. Since the latter two have the advantage of allowing oils to pass through, FrontStreet Coffee will use the darkest roasted coffee beans for this comparison—Sumatra Golden Mandheling.

All brewing parameters were identical, as follows:

• Coffee dosage: 15g
• Grind size: EK43 setting 11, with 75% retention on a #20 sieve (coarse sugar grind)
• Coffee-to-water ratio: 1:15
• Brewing water temperature: 88°C
• Brewing method: Three-stage pouring
• Filter cup used: Kono

We'll skip the brewing process and go straight to the results!

As you can see, when brewing dark roasted beans, the flow rate of this special non-woven filter paper isn't as fast as conventional non-woven filter paper, being closer to wood pulp filter paper. Therefore, when using it to brew dark roast coffee, we can apply the same parameters as usual. The conventional non-woven filter paper, however, showed under-extraction due to its faster flow rate. We would need to adjust the coffee grind finer to extract a proper cup of coffee (this is just a parameter issue, not a flaw in the filter paper—conventional non-woven filter papers also come in slow-flow versions).

Then, because this special non-woven filter paper has moderate gaps—neither as small as wood pulp filter paper nor as large as conventional non-woven filter paper—it can filter out oils while not allowing fine particles through. This enhances the coffee's aroma while maintaining cleanliness (conventional non-woven filter papers allow some fine particles to pass through). Therefore, it's more like a filter paper that combines the characteristics of both (wood pulp filter paper and conventional non-woven filter paper).

Advantages and Disadvantages

However, it has two drawbacks: first, it's not inexpensive—priced 2-3 times higher than the previous two types. It might be fine if you buy it just to try out, but if you want to use it in regular practice, you'll need to consider whether your wallet is thick enough (though perhaps this isn't a drawback? ). Second, because the liquid flow channels are restricted, when we brew light roast coffee, the flow is already slow due to the high-density coffee bed, and adding the filter paper's own restrictions will make the flow even slower. If we adjust the grind to increase flow rate, we risk under-extraction, making it somewhat unfriendly for beginners.

Those are the only two drawbacks—other aspects are quite good!

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473