Should You Sieve Out Fine Particles When Brewing Pour-Over Coffee? What Size of Coffee Grounds Are Considered Extra Fine? What Is the Role of Fine Particles?

It's only when brewing becomes blocked that people recall the fear of being dominated by fine particles!

"Flow restriction" has become a well-known technique for avoiding bitterness, and this is closely related to fine particles. When fine particles cause blockage during brewing, if flow restriction isn't applied in time, negative flavors like bitterness, astringency, and burnt notes will rush in, becoming debuffs for the coffee! This creates a certain impact on the drinker's taste buds and spirit. So often, after multiple disturbances from fine particles, some friends begin to practice the habit of filtering out fine particles before brewing.

However, FrontStreet Coffee doesn't recommend unconditionally filtering out all fine particles in every situation. Although fine particles can cause blockages during brewing, this is only probabilistic. In the vast majority of cases, they actually provide positive enhancements to the coffee!

What Exactly Are Fine Particles?

Generally, the particle size of ground coffee we use mostly falls within the range of 0.6-0.8mm, which is a normal grinding value. The coffee particles smaller than 0.25mm produced during grinding are what we call fine particles. These fine particles are similar to flour - if they don't clump together, they're easily overlooked by the naked eye.

How Exactly Are Fine Particles Produced?

Fine particles are mainly generated from collisions when coffee beans are ground. We can imagine it like this: when a piece of glass falls from a high place to the ground, besides large fragments, there are also many tiny fragments - the same principle applies to coffee beans! Coffee beans have different brittleness after roasting due to differences in density and roast level. The darker the roast, the higher the brittleness, and beans with higher brittleness are more likely to produce extremely fine particles because, like glass, they're more likely to shatter from impact. This is why they often require coarser grinding - not just because they're easily extracted, but also to reduce the amount of fine particles.

In addition to bean brittleness, the quality of the grinder is also a key factor determining the amount of fine particles produced. No matter which coffee blogger you ask, when ranking the importance of factors for brewing a good cup of coffee, besides the beans themselves, the grinder is the most crucial. Higher quality grinders produce more uniform particles and therefore fewer fine particles, and vice versa. But it's important to know that even high-quality grinders still produce fine particles because, as mentioned above, their production is affected by the brittleness of coffee beans. No matter the price or quality of the grinder, the ground coffee will never be absolutely uniform. The difference in grinder quality lies in the uniformity of the grind and the burrs used (for details, you can refer to FrontStreet Coffee's previous articles).

Why Can't All Fine Particles Be Removed?

Because the presence of fine particles allows coffee to have richer layers! As we all know, to make a delicious coffee with rich layers, the first thing we need to achieve is uniform extraction. However, the uniform extraction mentioned here might be different from what you imagine, because what most people associate with uniform extraction is that every coffee particle achieves the same extraction rate, when in fact, this is not the case.

As mentioned earlier, the particles ground by a grinder are not absolutely uniform - there are large ones and small ones. Therefore, when facing the same extraction efficiency, they release flavor compounds in different proportions. Coarser particles will be extracted less, while finer particles will be extracted more!

The three flavors of sour, sweet, and bitter have different major release points due to differences in molecular size. Sour and sweet substances are released in large amounts in the early stages, while bitter substances release slightly later (though all release throughout the entire process!). Because of this, affected by particle size, each coffee particle releases flavor proportions differently. Under-extracted particles release more sour and sweet substances, while over-extracted particles release more bitter substances. It is precisely these different quantities of substances that together create a cup of coffee with rich layers. However, if we filter out all fine particles, although each coffee might achieve very uniform extraction, it also means it lacks certain bitter substances. Without these bitter substances, it won't have overly rich layers, after all, sour, sweet, and bitter are mutually balancing elements.

Therefore, FrontStreet Coffee doesn't recommend filtering out fine particles all the time, as this would reduce the layered quality of the coffee. Only when the grinder quality is inadequate, leading to excessive fine particles (exceeding 10% of the total coffee amount) and causing drainage blockage or muddy coffee beds, should we filter out these fine particles~

- END -

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473