How to Determine if Filter Paper is Aligned with the Dripper? Why Should Filter Paper Be Wet with Water to Adhere Closely When Brewing Coffee?

For most people, wetting the filter paper is the default first step before brewing coffee. There are two main purposes: first, to ensure the filter paper adheres properly, and second, to wash away dust particles adsorbed on the paper. If using hot water, it can also preheat the equipment. In most tutorials, besides guiding us on how to make the filter paper fit snugly against the filter cup, there's usually some emphasis on the importance of proper adhesion for coffee extraction. However, few mention how much the degree of filter paper adhesion actually affects the final taste of coffee.

FrontStreet Coffee will conduct two rounds of experiments today, using filter papers with different degrees of adhesion to brew coffee, then taste and compare them one by one to see how the final flavor performances differ.

Experiment Setup

The filter cups used are the commonly available V60 and KONO. For coffee beans, we selected representative fruity acid and nutty types respectively. The specific brewing parameters are as follows:

V60 Group

• Coffee beans: Guatemala·Flower Goddess
• Bean amount: 15g
• Water ratio: 1:15
• Grind size: EK43s setting 10
• Water temperature: 90°C
• Pouring method: Three-stage pour

KONO Group

• Coffee beans: Brazil·Red Bourbon
• Bean amount: 15g
• Water ratio: 1:15
• Grind size: EK43s setting 10.5
• Water temperature: 87°C
• Pouring method: Three-stage pour

As the focus of this experiment, FrontStreet Coffee divided the filter paper adhesion into three groups: The first group has the filter paper perfectly fitted to the filter cup with no air bubbles in between; the second group has the filter paper placed off-center, resulting in half adhered and half hollow; the third group has the filter paper completely not adhered, with hollow spaces or large air bubbles on both sides.

V60 Group Comparison

The brewing times for the three pots of coffee were 1 minute 54 seconds, 2 minutes 4 seconds, and 2 minutes 12 seconds respectively. The TDS values measured with a concentration meter were 1.12%, 1.19%, and 1.26% in order.

Flavor performance: The three pots of washed Flower Goddess brewed with V60 showed basically consistent flavor profiles, all displaying light floral notes, lemon acidity, yellow stone fruits, almonds, and green tea tones. Using the first pot as a reference, the latter two pots with non-adhered filter paper had greater body weight, with both acidity and bitterness being more pronounced. Particularly, the third pot with completely non-adhered filter paper showed slight astringency in the aftertaste.

KONO Group Comparison

The extraction times for the three pots of pour-over were 2 minutes 7 seconds, 1 minute 54 seconds, and 1 minute 46 seconds respectively. The TDS values measured with a concentration meter were 1.13%, 1.06%, and 0.98% respectively.

Flavor performance: Compared to the previous group of fruity acidic coffee, the three pots of Brazilian Cerrado brewed with KONO showed distinct differences in flavor upon entry. The first pour-over had aromas of creamy chocolate, caramel biscuits, and Pu'er tea, with overall balanced mouthfeel and strong sweet aftertaste. In contrast, the second pot had only faint chocolate notes, with weaker roasted flavors and a slightly watery feel. The final pot had almost no aroma, with a rough mouthfeel dominated by burnt bitterness. FrontStreet Coffee suspects this was due to under-extraction of the coffee.

Analysis and Conclusion

At this point, attentive readers can probably draw a conclusion: when the filter paper doesn't adhere to the filter cup, regardless of whether using the fast-flowing V60 or the slower-flowing KONO, it actually changes the water drainage speed within the coffee bed, while simultaneously affecting the final extraction rate and concentration. Although the general flavor direction of the coffee doesn't change, the taste experience will be different.

Many people know that the V60's multiple spiral rib design helps coffee particles absorb water and expand, while allowing water flow to compress the coffee bed, creating richer layering. In the first group of experiments, FrontStreet Coffee observed that when the filter paper doesn't adhere to the filter cup, the coffee grounds will be in a "one-sided" state - one side pressed against the filter cup edge, while the other side is "exposed" to the air.

Although there were no problems during the initial bloom stage, as the water level gradually rose, large bubbles continuously emerged from the parts where the filter paper wasn't adhering. This is because without the rib support, it couldn't clear pathways through the coffee bed, so water flowed toward other adhered areas, resulting in uneven extraction. Also because water flow encountered obstacles, extraction time was forced to extend, making the coffee prone to over-extraction.

Compared to V60, the KONO filter cup has smooth inner wall curves. This design ensures that after wetting, the filter paper adheres tightly to the filter cup edge. Additionally, the entire filter cup only has flow-guiding ribs on the bottom quarter of its height, thus restricting upward airflow movement. Water can only pass through the bottom into the server below. This design not only allows sufficient contact time between coffee grounds and water but also creates better immersion effects during extraction. When brewing dark roast coffee, it can better express rounded and full-bodied characteristics.

Therefore, when using KONO to brew coffee, we should try to ensure the filter paper adheres properly before adding coffee grounds and pouring water. Otherwise, during the extraction process, a "channel" will quietly form somewhere in the filter cup, allowing water to flow directly through the hollow areas, resulting in under-extraction. The coffee's mouthfeel will become thin and rough.

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473