Analysis of Slow Pour-Over Coffee Flow Rate: What to Do When Coffee Won't Drain Properly?

Pour-over coffee, as a representative of drip extraction, can be seen as a process where water is first poured into coffee grounds, allowing it to flow through the coffee bed and drip into the server below. With the assistance of a digital scale, we can effectively control the pouring time, but the total time for water to flow into the server is influenced by factors such as coffee grind size, water absorption of the particles, pouring technique, and dripper structure (filter paper material). Therefore, it's impossible to precisely control the total duration of coffee drip extraction.

For many beginners, time is the most accessible standard for testing flow rate. When all the target water has been poured and the coffee liquid in the dripper drips completely into the server within the expected 2 minutes, it indicates that various brewing parameters are within a reasonable range. However, if the duration significantly exceeds (30 seconds to 1 minute) or falls far short of 2 minutes, it means there might be an issue in some aspect that needs to be identified and addressed promptly.

Among all the extraction time questions that FrontStreet Coffee has answered, the most common situation is where the flow rate slows down too much in the final stage, forcing the extraction time to extend. We typically describe this as the coffee "pooling" or "waterlogging" at the end. So what's the solution?

Severe Pooling: Does It Affect Coffee Taste?

Regardless of the method we use to make coffee, the extraction principles are similar. For immersion brewing methods, short extraction times result in coffee that is weak and flavorless, while long extraction times lead to coffee that is strong, bitter, and astringent—examples include cold brew and French press. Similarly, the longer the drip time for pour-over coffee, the more contact time between coffee and water, releasing more soluble flavor compounds. Consequently, the probability of over-extraction also increases.

When pooling occurs in the final stage, if we observe the coffee bed carefully, we'll notice that the foam on the surface is very thin, appearing light yellowish-white, and sometimes there's no foam at all, just water accumulated in the dripper. This phenomenon indicates that most coffee grounds have settled at the bottom, blocking the water's passage. By the time it slowly enters the server, it has likely extracted too many soluble substances from the coffee. These late-releasing large molecules are predominantly bitter and unpleasant, resulting in coffee that doesn't taste good.

Why Does the Water in the Final Stage Drains So Slowly?

As mentioned earlier, coffee grounds are the key factor blocking water flow. The finer the grind, the greater the resistance and the slower the flow rate. Generally, coffee grounds used for pour-over are about the size of sugar granules. If sifted through a #20 sieve, the appropriate grind size would have about 70-80% of the grounds passing through. However, grinding can never be perfectly uniform—in other words, coffee grounds will inevitably contain a mixture of coarser and finer particles.

Typically, severe pooling in the final stage (when coffee liquid hasn't completely dripped through after 2 minutes and 20 seconds) is caused by poor grinding quality from the grinder, producing too many extremely fine particles. During the circular pouring process, water acts as a fluid that moves the coffee grounds. Following the stirring path, smaller fine particles will be the first to "get stuck" in the filter holes at the bottom, obstructing the penetration of hot water.

If brewing light-roasted, fruit-acidic coffee beans, first, the bean structure is more compact with weaker water absorption. Second, the higher bean density makes them more likely to sink to the bottom first, resulting in blockage and accumulation.

Beyond the impact of grinding, pouring technique can also cause water blockage in the final stage. Some people are accustomed to pouring in very large circles when brewing. This technique allows the water level to rise gradually in the early stages, but in the later stages, the water flow from large circles tends to "hit" the filter paper, washing down the previously accumulated powder walls on the dripper sides all at once to the bottom, causing blockage.

Similarly, regarding coffee bed management issues, if the initial pouring is too gentle and doesn't properly stir and raise the coffee bed, causing it to accumulate at the conical angle, then by the third pouring stage, even with a large water flow from a raised spout, it's difficult to "rescue" the low coffee bed. The coffee liquid can only drip down along the dripper by gravity.

After understanding the principles, we need to identify the specific problems.

Finding the "Culprit" Causing Pooling

Whether you're brewing dark or light roast beans, if the final coffee bed looks like a wet slurry as shown in the picture below, the time often exceeds 2 minutes, and the coffee has a dull, muddy taste, then it indicates that your grinding equipment is producing too many fine particles. To solve this type of problem, the most effective approach is to directly switch to a grinder with better grinding quality. After all, grinding burrs with higher precision can significantly reduce the troubles caused by extremely fine particles.

Without changing equipment, FrontStreet Coffee suggests trying to adjust the grind to be coarser first. With overall coarser particles, the corresponding fine particles will also be appropriately reduced. Additionally, switching to a dripper with faster flow rate can effectively solve the problem of slow drainage, such as the Hario V60 or the Ice瞳 B75 that FrontStreet Coffee commonly uses.

If we only experience slow flow rates when brewing light-roasted beans and want to avoid the negative flavors caused by prolonged "waterlogging," we might consider adjusting our technique.

Take FrontStreet Coffee's commonly used three-stage pouring method as an example. After blooming, first pour with a vertical large water flow from the center, maintaining a circular pattern about the size of a coin. You can see foam continuously emerging from the center, and as the water level rises, the coffee grounds are gradually pushed to the edges, forming a powder wall about 2/3 high. The final stage uses a small water flow, still maintaining a small circular range. This allows for more uniform contact between coffee and water while avoiding the coffee grounds at the edge of the dripper being washed down.

- END -

FrontStreet Coffee

No. 10, Bao'an Qianjie, 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