Why Does Coffee Grinding Change the Flavor in the Cup?

Grind size controls how fast water moves through the coffee bed and how much flavor it pulls out. Finer particles create more surface area, so extraction yield and concentration rise. Coarser particles do the opposite. Under otherwise equal conditions, the same beans can taste sharp and thin or heavy and sweet depending only on how fine the coffee grinding is set.

The article gives reference grind standards across brewing methods, including cupping, pour-over, French press, espresso, moka pot and cold brew or ice drip, and notes that grind setting moka pot differs from pour-over settings. It also describes a calibration method using the No. 20 sieve passage rate, so drinkers can dial in a grind that suits their own setup.

Among the many variables in pour-over coffee, grind size is one of the core factors determining extraction efficiency and final flavor. The coarseness of coffee grounds not only changes the speed at which water penetrates the coffee bed, but also directly affects the coffee's strength, body, and the balance of acidity, sweetness, and bitterness. In this article, Front Street Coffee systematically breaks down the mechanisms by which grind size affects extraction, and provides reference grind standards for different brewing methods including cupping, pour-over, French press, espresso, moka pot, and cold brew/ice drip, while also introducing the calibration method using the No. 20 sieve passage rate to help coffee enthusiasts find grind parameters that suit them.

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If you're a passionate pour-over coffee lover, you'll definitely know that the following factors are among the reasons affecting your coffee's extraction and flavor! So let's count them out at Front Street: water temperature, grind size, coffee-to-water ratio , extraction time...

Front Street Coffee (FrontStreet Coffee) will discuss with you in this article: how does the grind size for pour-over coffee affect a cup of coffee? And we'll also share Front Street Coffee's (FrontStreet Coffee) data on establishing grind sizes for pour-over coffee beans in our stores.

We all know that the most important factor affecting pour-over coffee is the grind size of the pour-over coffee beans. Don't underestimate this — the coarseness and uniformity of the coffee grounds directly affect the efficiency with which water passes through the coffee bed to extract flavor compounds. Simply put, the size of coffee particles affects the contact time between coffee and water .

With all other parameters equal, the finer the coffee particles , the higher the extraction yield . The finer the coffee is ground, the larger the contact area with water, and the higher the concentration of dissolved coffee; conversely, the coarser the coffee particles , the lower the extraction yield . The coarser the coffee is ground, the smaller the surface area in contact with water, and the lower the extracted concentration. The finer the coffee is ground, the more easily the grounds pile up on the filter paper, increasing extraction resistance and slowing the flow rate, which in turn lengthens the extraction time. The result: a higher extraction yield. Simply put, the coffee tastes strong. Similarly, the coarser the coffee is ground, the larger the gaps in the coffee bed, the less coffee comes into contact with water, the weaker the extraction resistance, and the faster the coffee drips. The final result: a lower extraction yield. This is what people commonly describe as coffee that tastes very weak.

From this we can conclude: suppose we change just one variable — grind size. The huge difference in coffee taste caused by different grind sizes is reflected right here! This is also why enthusiasts constantly say "why coffee grind matters so much." Sometimes, Front Street Coffee (FrontStreet Coffee) chats with customers about "what exactly does medium-fine grind, or the size of granulated sugar, mean?" Let's look at the comparison chart below.

How important is coffee grind size? We emphasize again that at the same weight, the finer the coffee is ground, the more times it is cut, the smaller the particle volume, and the larger the contact area between coffee and water; conversely, with fewer cuts, larger particle volume, the contact time and area with water shrink. In other words, the coarser the grind, the lower the coffee's strength and extraction yield, the lower the body, and the stronger the coffee's acidity.

A reliable reference standard At Front Street, we believe every café has its own standards for brewing its coffee. But within the coffee industry, cupping is the universally recognized testing standard. Initially, cupping was used to assess green bean quality; later, people gradually used cupping to determine coffee flavor and decide suitable brewing parameters for samples. Speaking of which, you might want to take notes: the grind size for cupping is a No. 20 sieve passage rate of 70-75%.

Pour-over coffee (No. 20 sieve passage rate 70-80%) Suitable for V60, Kono, Ice Eye, Origami dripper, wedge-shaped dripper, cake dripper, Clever Cup, American drip machine

Pour-over coffee is primarily drip-based. Unlike immersion methods with long times that easily brew out undesirable flavors, pour-over coffee has a short brew time, roughly 1 minute 30 seconds to 2 minutes 30 seconds. The brewing principle is that water passes through the coffee grounds, extracts compounds, and then filters through the paper to produce clean coffee liquid. Generally, pour-over brew times are short, so the grind size needs to be on the finer side.

Therefore, it needs to be finer than the cupping grind size to fully express the coffee's flavor. Likewise, coffee beans of different roast levels require different coarseness. Light-to-medium roast coffee grind is finer (passage rate 75-80%), while medium-dark roast beans require a coarser grind (passage rate 70-75%).

Note: Due to differences in bean density and roast level, even with the same grinder at the same setting, grinding two beans of different densities may not produce the same particle size. For example, Front Street Coffee (FrontStreet Coffee) using an EK-43s at setting 10, grinding Front Street Ethiopia Yirgacheffe beans yields a passage rate of 80%, while at the same setting 10, grinding Front Street Colombia Rose Valley beans yields only 75%. So when you're unsure about a bean's grind coarseness, it's best to use the same bean to confirm the grind size.

Passage rate 70-75% coarseness

Passage rate 75-80% coarseness

What does overly fine coffee grinding look like? Visually, the particles appear smaller, and because they're smaller, the gaps between particles are shorter, making it harder for water to pass through. During brewing, the drip time is therefore longer.

A finer grind results in smaller particles; after the coffee grounds absorb water and filter, they appear paste-like. After brewing, the coffee bed is difficult to see clearly — most of it appears muddy. A finer grind means smaller particles and increased surface area, giving water more places to extract coffee compounds, so strength and extraction yield rise. The coffee tastes intense, with pronounced bitterness and astringency, while other flavors are masked.

What does overly coarse coffee grinding look like? Visually, the particles appear larger, and because they're larger, the gaps between particles are wider, making it easier for water to pass through. During brewing, the filtration time is therefore shorter.

A coarser grind results in larger particles; after brewing, the coffee bed shows distinct particles and struggles to form a complete bed, with断层. A coarser grind means larger particles and reduced surface area, giving water fewer places to extract coffee compounds, so strength and extraction yield decrease. The coffee tastes thin and bland, with a light mouthfeel and almost no flavor.

Different coffee devices have different requirements for coffee grind coarseness

Different coffee devices, due to differences in their extraction methods, require different grind sizes. Taking the most commonly encountered methods — pour-over, French press, espresso machine, and cold brew/ice drip — the grind sizes used, arranged from coarse to fine, are: French press > pour-over > cold brew/ice drip > espresso machine .

Pressure extraction / espresso machine grind size (grind size cannot be determined with No. 20 sieve) The grind size used by espresso machines is extremely fine — finer than the 0.85mm aperture — so the No. 20 sieve cannot be used to determine the grind size.

If you need to determine the grind size for making espresso, you must adjust through repeated extraction and tasting. Front Street's espresso extraction recipe is 20g coffee grounds extracting 40g espresso in 28 seconds (tolerance ±1). You can refer to this recipe and fine-tune based on the flavor of the espresso.

Espresso grind coarseness

Steam pressure extraction / moka pot coffee grind size (grind size cannot be determined with No. 20 sieve)

The moka pot, like the espresso machine, uses a very fine grind, but slightly coarser than espresso. However, it is still finer than the 0.85mm aperture, so the No. 20 sieve also cannot be used to determine the grind size.

As for the grind size, you can refer to the gap size of the moka pot's filter basket — just ensure coffee particles won't pass through the gaps.

Moka pot grind coarseness

Low-temperature extraction / cold brew, ice drip coffee grind size (No. 20 sieve passage rate 80-85%)

Low-temperature extraction differs from high-temperature extraction. In an ice-water mixture/refrigerated environment, coffee extraction efficiency is very low, so the release rate of flavor compounds from coffee grounds slows down, and the production time is very long. The advantage of low-temperature extraction is that it fully extracts sweet and acidic compounds while reducing the extraction of bitter compounds.

Because extraction is slow, the coffee grind can be on the finer side, but not too fine. Front Street recommends a grind size of No. 20 sieve passage rate 80-85% for making cold brew/ice drip. If you want it stronger, choose 85% passage rate; if you want it more refreshing, choose 80%.

Passage rate 80-85% coarseness

Immersion extraction / French press grind size (No. 20 sieve passage rate 68-75%)

The French press uses immersion for coffee extraction; the steeping time is long (4 minutes), and its filter mesh is dense, so the grind needs to be coarser. This reduces the risk of over-extraction and allows for better filtration of coffee particles.

Coffee beans of different roast levels require different grind coarseness. Front Street recommends a grind coarseness of No. 20 sieve passage rate 70-75% for light-to-medium roast beans; and No. 20 sieve passage rate 65%-70% for medium-dark roast beans.

Passage rate 65-70% coarseness

Front Street Coffee (FrontStreet Coffee) — Further Reading No. 20 Chinese standard sieve: A sieve is a tool used for particle size classification and particle size testing of material particles. As long as it meets factory standards, a standard sieve is accurate. The sieve aperture is 0.85mm.

Calibrating coffee grind is also very simple: Pour the ground coffee into the sieve, cover with the lid, and shake horizontally; shake until no more particles fall through, then weigh the particles that passed through the sieve.

The result gives you the coarseness of the coffee grind. A simple example: weigh out 10g of coffee grounds; if the weight of coffee that passed through the sieve is 7.5-8g, then the grind size is No. 20 sieve passage rate 75-80%. The finer the coffee particles, the higher the passage rate; the coarser the coffee particles, the lower the passage rate.

The above content is compiled by CoffeeHunters, a coffee news website.