How Do Coffee Particles Decide the Right Grind Size?

Grind size is the main variable that decides how a cup tastes. Coarse coffee particles release flavor slowly, so too-coarse grounds taste weak; too-fine grounds pull out bitter, muddled flavors. The grind ranges rank from coarse to fine as French press, pour-over, cold brew or iced drip, then espresso machine.

A cupping standard, measured as the pass-through rate of a No. 20 sieve, serves as the unified ruler for these ranges. Roast level and bean density also shift the result, so the same setting can behave differently between beans. A dialed-in how does espresso machine work routine tracks dose, yield, and time rather than grinding by feel.

When brewing a good cup of coffee, grind size is an unavoidable key variable. If the particles are too coarse, flavor release is insufficient; if ground too fine, it easily brings out bitter and muddled off-flavors. But just how coarse counts as coarse, and how fine counts as fine? And how should you convert between different brewers? This article uses the industry-recognized cupping standard as its baseline, with the No. 20 sieve pass-through rate as a unified ruler, to give reference grind ranges one by one for French press, pour-over, cold brew/iced drip, and espresso machines, explains how roast level and bean density affect grinding results, and finally includes Front Street Coffee's approach to dialing in espresso extraction, helping you turn grind size from "by feel" into "by data."

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No matter which brewing tool you choose, the first step is always grinding coffee beans into grounds, and the point of this is to accelerate the release of flavor compounds. However, not all the components that can be dissolved out of coffee are pleasing. To extract as much of the good-tasting part as possible while preventing undesirable flavors from being pulled out, you need to nail down the right degree of extraction—and the coarseness of the coffee particles is precisely the core variable in this.

The coffee grind size corresponding to different brewing devices varies

Because the extraction principles of various devices differ, their requirements for grind size also differ. Taking the pour-over, French press, espresso machine, and cold brew/iced drip that we encounter most often in daily life, they can be ranked from coarse to fine as: [French press > pour-over coffee > cold brew/iced drip > espresso machine].

Although we roughly know which extraction method needs a coarser grind and which needs a finer grind, it is hard to state the specific values—just how coarse "coarse" actually is, just how fine "fine" goes, and what exactly this "relatively" is being compared to.

A reliable reference baseline

Although coffee brewing standards each have their own approach, there is one standard widely recognized in the industry, and that is cupping! Cupping was originally used to evaluate the quality of green coffee beans, and this method also has something worth borrowing at the extraction level. The grind size used in cupping is a No. 20 sieve pass-through rate of 70–75%.

[Science note: The aperture of the No. 20 Chinese standard sieve is 0.85 mm. It is a tool used to classify and test the particle size of substances. As long as it meets factory standards, the sieve is accurate. The method for calibrating coffee grind size is also very simple: pour the ground coffee into the sieve, put on the lid, shake horizontally until no more particles fall through, then weigh the grounds that passed through the sieve to determine the coarseness level. For example, take 20 g of coffee grounds; if 15.2 g passes through the sieve, then this grind size is a No. 20 sieve pass-through rate of 76%. The higher the pass-through rate, the finer the grind.]

Since cupping can use a standard sieve to calibrate and determine grind size, the grind sizes corresponding to the brewing devices we use daily can likewise be clearly listed with specific data.

French press (No. 20 sieve pass-through rate 68–75%)

The extraction logic of the French press is very close to cupping, mainly based on immersion, so the grind level it uses is highly consistent with cupping. Choosing relatively coarse particles has another consideration: the French press relies on a metal filter for filtration, and the mesh gaps are visible to the naked eye, so grinding coarser allows filtration to be completed better. Beans of different roast levels also differ in coarseness: medium-light roasted coffee beans can be ground finer (pass-through rate 72–75%), while medium-dark roasted coffee beans are better ground coarser (pass-through rate 68–71%).

Pour-over coffee (No. 20 sieve pass-through rate 70–80%)

Pour-over is mainly a drip filtration method. Unlike immersion, its brewing time is short, roughly between 1 minute 30 seconds and 2 minutes 30 seconds, so it is not easy to drag out off-flavors. Precisely because of this, pour-over requires a finer grind than cupping in order to fully express the coffee's flavor. Likewise, different roast levels require different coarseness. Medium-light roasted coffee is suitable for a finer grind (pass-through rate 75–80%), while medium-dark roasted coffee beans should be ground coarser (pass-through rate 70–75%).

Cold brew/iced drip coffee (No. 20 sieve pass-through rate 80–85%)

Both cold brew and iced drip use cold water for extraction. Water's penetrating ability is weaker, and extraction efficiency is quite low. Therefore, the coffee must be ground finer—but remember, finer is not always better: grinding too fine will make cold brew cloudy and also increase filtration difficulty; it will also cause water to pool in the coffee bed of iced drip, preventing water from passing through smoothly. Therefore, a grind size with a No. 20 sieve pass-through rate of 80–85% is more appropriate. If you want it richer, choose a pass-through rate of 85%; if you want it lighter and more refreshing, choose a pass-through rate of 80%.

Note: Due to differences in coffee bean density and roast level, even if you use the same grinder at the same setting to grind two beans with large density differences, the resulting particle coarseness may not be the same. For example, when grinding Front Street Coffee Yirgacheffe coffee beans using EK-43s at setting 10, the corresponding sieve pass-through rate is 80%; while when grinding Front Street Coffee Colombia Pink Bourbon, also using setting 10, the sieve pass-through rate is only 75%. So when you feel the grind size seems off, it is best to use the same bean to confirm the grind size.

Espresso machine

The grind size used by espresso machines is extremely fine, and using a sieve to sift it is not realistic. Judging espresso grind size mainly relies on extraction tests. Before opening for business every day, coffee shops must dial in their espresso, and a large part of that work is adjusting grind size. Coffee machines are extremely sensitive to the coarseness of coffee grounds; even if the grind setting differs by only 0.1 step, the extraction time and flavor will show noticeable changes.

Therefore, determining the grind size for an espresso machine is premised on having a stable espresso extraction recipe. Take Front Street Coffee as an example: its espresso extraction recipe is 20 g of coffee grounds extracting 40 g of coffee liquid within 28 seconds (with an allowable error of plus or minus 1). First fix this recipe, then adjust the grind size to achieve it, and afterward decide based on the flavor you taste whether fine-tuning the parameters is needed.

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