Why Does the Liquid in the Filter Cone Become Transparent During Extraction? How to Prevent Pour-Over Coffee Blockage?

Yesterday while FrontStreet Coffee was browsing online, we came across an interesting question. The original post can be summarized as follows: during the brewing process, the liquid in the filter cup should be in a state covered by foam with low transparency, as shown below:

However, sometimes during brewing, we end up with a transparent liquid state with no obstructions and high visibility, as shown below:

So what's happening here? Some "experienced" friends might immediately recognize the issue. That's right - the brew is likely blocked! This situation indicates that during prolonged extraction, the fine particles and foam floating on the surface have settled or dispersed to the sides without being replenished, creating the highly visible liquid state in the filter cup. This occurrence means the coffee extraction has been affected, and the final result will most likely not taste good. Therefore, if you encounter this phenomenon, FrontStreet Coffee suggests making adjustments from the following aspects:

1. Grind Size

Blockages frequently occur when brewing light roast coffee beans. Light roast beans have lower extraction efficiency, so to achieve sufficient extraction, people usually adjust the grind to be finer, which increases the amount of fine particles. Regardless of the grinder used, coffee particles will contain some fine powder - the less precise the grinder, the more fines. Excessive fine particles have a higher chance of clogging the filter paper holes during brewing, ultimately causing the coffee to become over-extracted due to excessively long extraction times.

Therefore, we can适当 coarsen the grind and increase water temperature to improve extraction efficiency! For example, when FrontStreet Coffee brews light roast beans, we use water temperature between 92°C-90°C, with an Ek43 grind setting of 10, achieving 75% pass-through rate on a #20 sieve. These parameters have a higher fault tolerance. While ensuring extraction rate, blockages occur less frequently. Alternatively, we can use a sieve to remove the fine particles causing blockages without adjusting the grind.

2. Brewing Technique

Because light roast beans have more intact fibers and greater density compared to dark roast beans, they tend to sink more easily when saturated with water during brewing. If the water flow we pour during brewing has insufficient penetration force to "lift them up," they will continue to accumulate at the bottom, causing blockages. Therefore, FrontStreet Coffee recommends increasing the water flow when brewing light roast coffee to enhance penetration power, allowing the coffee particles accumulated at the bottom to tumble and reduce the occurrence of blockages.

3. Filter Cup

Different filter cup designs can change the percolation speed of coffee liquid. For example, both V60 and Kono are conical filter cups, but when we use the same parameters and brewing methods to extract coffee, their extraction completion times are completely different. The Kono, with its small holes and no ribbing, will be much slower.

Therefore, when brewing light roast beans that are prone to blockages, if using a filter cup with slower flow rate, we need to adjust the parameters and methods used during brewing (coarsening the grind) to reduce the chance of blockages. Besides these factors affecting blockages, there's another element that can increase the transparency of liquid in the filter cup - bean freshness!

Bean Freshness

When coffee beans have been stored for a long time (over two months), and the carbon dioxide that hinders extraction has mostly dissipated, the foam produced during brewing will decrease, and the liquid visibility will be higher. Additionally, the coffee beans become easier to extract soluble substances from. If we continue to use conventional brewing methods for extraction, it will be very easy to extract negative substances that affect the coffee flavor.

Therefore, when brewing coffee beans that aren't as fresh, we can appropriately slow down the extraction efficiency. Speeding up extraction time, lowering water temperature, or coarsening the grind will all be good options.

- END -

FrontStreet Coffee

10 Bao'an Front Street, Yandun Road, Dongshankou, Yuexiu District, Guangzhou, Guangdong Province

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473