Should You Use Hot Water or Room Temperature Water to Wet Your Filter Paper?

Most coffee enthusiasts wet their filter paper before brewing. This practice primarily ensures the filter paper fits snugly against the filter cup, preventing hot water from bypassing the coffee grounds and seeping directly into the lower pot. Additionally, it reduces the amount of coffee liquid absorbed by the filter paper during the blooming stage, and addresses the now rarely mentioned issue of removing any paper taste.

For those who habitually wet their filter paper, a common question arises: should you use hot water or room temperature water for this process?

This question emerges because many brewing devices do indeed transform coffee when heated. For example, heated espresso machine portafilters extract espresso with richer aromas, and preheated cups or pots slow down the cooling rate of coffee. However, logically speaking, if wetting filter paper with hot water were to cause changes in coffee flavor, these changes wouldn't originate from the paper itself, but rather from the filter cup that the paper adheres to.

Water temperature can only affect the filter paper in terms of removing taste; it's the "filter cup" that influences coffee flavor changes due to temperature variations. The filter paper merely serves as a medium establishing this relationship. Today, let's conduct several experiments to observe what differences emerge when using water at different temperatures to wet the filter paper!

Experimental Comparison by FrontStreet Coffee

FrontStreet Coffee will conduct this experiment using filter cups made from three different materials: resin, ceramic, and copper. Each group will use either room temperature water or hot water above 90°C to wet the filter paper, examining the differences in the extracted coffee liquid.

Brewing Parameters

This experiment uses a light-medium roast Ethiopian Santa Vani coffee bean, with 15g of coffee, a 1:15 coffee-to-water ratio (225ml of water), water temperature at 92°C, EK43 grind setting 10, and a three-pour brewing method.

1. Resin Filter Cup

Room temperature group: Coffee liquid temperature at 65°C, concentration at 14.9%.
Hot water group: Coffee liquid temperature at 67°C, concentration at 14.7%.

2. Ceramic Filter Cup

Room temperature group: Coffee liquid temperature at 66°C, concentration at 14%.
Hot water group: Coffee liquid temperature at 71°C, concentration at 14.4%.

3. Copper Filter Cup

Room temperature group: Coffee liquid temperature at 66°C, concentration at 14.3%.
Hot water group: Coffee liquid temperature at 70°C, concentration at 14.5%.

Flavor Evaluation

In terms of flavor, all groups showed surprisingly consistent notes: pineapple, mango, and citrus. However, coffee brewed with room temperature water exhibited sweeter flavors, while coffee brewed with hot water displayed more vibrant acidity.

Reasons for the Differences

When you use hot water to wet the filter paper, as mentioned above, the filter cup directly absorbs heat and increases in temperature. During the brewing process, this preheated filter cup not only avoids absorbing heat from the blooming water but also increases the extraction rate to some extent.

Acidic compounds are the first to be extracted from coffee. When you increase extraction intensity in the early stages, acidity naturally becomes more pronounced, which explains why the hot water group exhibited more noticeable acidity.

The room temperature group showed the opposite effect. Since hot water wasn't used to wet the filter paper, both the filter cup and serving pot remained at room temperature. During the blooming stage, the room temperature filter cup absorbed some heat from the blooming water, resulting in slightly lower extraction intensity and consequently less pronounced acidity.

As the temperature gradually increased, both sweet and acidic compounds were progressively extracted. Because the entire process maintained balanced extraction, you ended up with coffee that had both pleasant acidity and sweetness, making it seem comparatively sweeter than the hot water group.

In conclusion, the temperature of water used for wetting filter paper does indeed affect extraction rates to some extent. As for which temperature to choose, FrontStreet Coffee won't make a specific recommendation. Friends can decide based on personal taste preferences. Although the impact may be subtle, flexible application of this technique can help you brew your desired coffee flavors~

FrontStreet Coffee
No. 10, Bao'an Qianjie, Yandun Road, Dongshankou, Yuexiu District, Guangzhou, Guangdong Province

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