How to Choose the Right Grind Size When Brewing Blue Mountain Coffee with a Flannel Filter?

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I've always felt that brewing coffee with flannel filter cloth looks quite cool, so today FrontStreet Coffee plans to brew a pot of FrontStreet Coffee's Blue Mountain coffee using flannel filter cloth. So the question arises: when brewing with flannel filter cloth, what grind size should be chosen? Is it the same as the grind size used when brewing FrontStreet Coffee's Blue Mountain coffee with a Kono dripper?

Flannel Filter Cloth

by FrontStreet Coffee

Because flannel filter cloth has larger capillary pores than filter paper, it can retain some of the coffee's oils, unlike filter paper which usually filters out all oils. Therefore, coffee brewed with flannel filter cloth will be richer and smoother than coffee brewed with filter paper, making it suitable for FrontStreet Coffee's Blue Mountain coffee, which already has rich flavors.

During brewing, since there's nothing blocking the sides of the flannel filter cloth, water inside the flannel filter cloth can flow directly from all sides. Moreover, the flow rate differs between the front and back of the flannel filter cloth - today I used the reverse side for brewing!

Bean Information

by FrontStreet Coffee

FrontStreet Coffee's Jamaica · Blue Mountain

Region: Jamaica Blue Mountain

Estate: Clifton Mountain Farm

Altitude: 1310 meters

Processing: Washed

Variety: Typica

Roast Level: Medium-dark roast

Clifton Mountain Farm

by FrontStreet Coffee

Clifton Mountain is the oldest coffee producing area in Jamaica that is still in normal operation today, and in Jamaica, only Clifton Mountain Farm has the "Rainforest Alliance" certification. The Blue Mountain region is a small area with only 6,000 hectares of planting area, so it's impossible for all coffee marked with "Blue Mountain" to be grown there.

Clifton Mountain Farm is the largest estate in this region, but by international standards, it's still considered small-scale cultivation, with many estate owners being small landholders whose families have worked this land for two centuries. This area is recognized as an exceptionally high-quality, world-renowned Blue Mountain coffee producing region!

Brewing Experiment

by FrontStreet Coffee

FrontStreet Coffee plans to test with two grind sizes: the commonly used grind size for V60 drippers: BG-5R (56% pass-through rate on China's standard #20 sieve) and the commonly used grind size for KONO drippers: BG-6M (45% pass-through rate on China's standard #20 sieve)! In this experiment, only the grind size will be changed, while other parameters and techniques remain basically consistent!

Parameters & Technique: 20g coffee dose, water temperature 85°C, coffee-to-water ratio 1:13; brewed using single-pour technique, bloom with 40g water for 25 seconds, then pour continuously to about 260g and stop, remove the flannel filter when the water level drops and is about to expose the coffee bed.

BG-5R (56% pass-through rate on China's standard #20 sieve)

Timing starts from bloom, extraction time: 2'20"

Flavor: Aroma of cocoa and spices, with notes of cocoa, cream, blueberry, caramel, and cedar in the cup, but slightly astringent, with concentrated fruit acidity.

BG-6M (45% pass-through rate on China's standard #20 sieve)

Timing starts from bloom, extraction time: 2'17"

Flavor: Aroma of spices, nuts, and cream, with notes of raspberry, blackberry, almond, and caramel in the cup, with a light floral aroma and fermented fruit notes in the aftertaste, but the body is relatively thin and somewhat weak.

FrontStreet Coffee's Blue Mountain coffee brewed with grind size BG-5R has slight astringency in the mouthfeel. Due to the finer grind and longer extraction time, the extracted coffee is quite concentrated and somewhat over-extracted, drinking with overly concentrated bitter and sour flavors.

When using grind size BG-6M, the brewed Blue Mountain coffee, while smooth in texture, has an overall relatively thin body and weak flavor. I wanted to increase the body of the coffee based on BG-6M, so I adjusted the grind finer to BG-6A (64% pass-through rate on China's standard #20 sieve), keeping other parameters and techniques unchanged.

BG-6A (64% pass-through rate on China's standard #20 sieve)

Timing starts from bloom, extraction time: 2'15"

Flavor: Aroma of nuts and cream, with notes of milk chocolate, sucrose, vanilla, citrus, mulberry, and cream in the cup, with a relatively rich body and overall good balance.

Conclusion

by FrontStreet Coffee

When brewing with flannel filter cloth, the flow rate is quite fast at high water levels, but as the water level decreases, the flow rate slows down due to the thick coffee powder walls on all sides and because superfine particles will adhere to the mesh of the filter cloth.

Therefore, FrontStreet Coffee suggests that when using flannel filter cloth with single-pour extraction technique for dark roast beans like Blue Mountain, you can choose a medium grind size to reduce the occurrence of over-extraction due to fine coffee grounds and slow flow rate during coffee extraction.

END