How do coffee particles control extraction and flavor?

The size of the coffee particles sets how fast soluble flavor compounds release during brewing. Grind too coarse and the cup tastes weak; grind too fine and bitter, off-flavors appear. The general order from coarse to fine is French press, then pour-over, then cold brew and ice drip, with espresso at the fine end. Each brewer needs its own match.

Because grinders lack a unified scale, the same setting can differ between machines, so the No. 20 standard sieve with a 0.85mm aperture is used to classify and check particle size. Weigh how much passes through the sieve to compare settings objectively. This matters for any method, including how to use a drip coffee machine, where a medium grind usually keeps the cup balanced.

Whether a cup of coffee is light or bitter is often foreshadowed the moment the beans are ground. The coarseness of the coffee particles directly determines the release rate of soluble flavor compounds—it must fully extract the pleasant aromas and sweet-tart notes while avoiding the emergence of bitter and off-flavors. This article focuses on four common brewing methods—pour-over, French press, cold brew/ice drip, and espresso—explaining the grind range suited to each, and introducing how to calibrate grind size with a No. 20 standard sieve (0.85mm aperture), so that every bean can find its ideal brewing coarseness. The article also retains Front Street Coffee's empirical parameters from actual cupping and in-store dialing for coffee enthusiasts to reference.

Why is the coffee I brew myself always weak and flavorless? And why does it often carry an unpleasant bitterness? Most people's first reaction is that something went wrong with their technique, but the real answer often lies in the grind size. Once coffee beans are ground into powder, the release rate of soluble flavor compounds is closely related to particle size. Not all soluble substances in coffee are desirable, so it is necessary to find an appropriate coarseness that allows good flavors to be extracted as much as possible while suppressing the production of undesirable flavors.

Different brewing devices require different grind coarseness

Since each coffee device has a different extraction principle, the required grind degree naturally varies. Taking the most common types in daily life—pour-over coffee, French press, espresso machine, and cold brew/ice drip—arranged from coarse to fine particles, the order is roughly [French press > pour-over > cold brew/ice drip]. Extraction temperature, method, and time all differ, so to obtain coffee with a suitable concentration, each extraction method must be matched with a corresponding grind coarseness.

However, grinders usually do not have a unified scale standard, and the same setting on different machines can produce different coarseness. This is where a cupping calibration sieve comes in handy—the No. 20 Chinese standard sieve, with an aperture of 0.85mm.

How to use a coffee grind calibration sieve?

The No. 20 Chinese standard sieve has an aperture of 0.85mm. It is itself a tool for particle size classification and testing. As long as it meets factory standards, the sieve is accurate. The method for calibrating coffee grind size is simple: pour the ground coffee into the sieve, put on the lid, shake horizontally back and forth until no more particles fall through, then weigh the powder that passed through the sieve. For example, take 10g of coffee powder; if 7.5g passes through the sieve, then this grind size has a No. 20 sieve pass rate of 75%. The higher the pass rate, the finer the grind.

How to judge whether the coffee grind coarseness suits your brewing method?

Whenever Front Street Coffee receives a new bean, it first does a cupping. The core purpose of cupping is to confirm flavor performance and quality control status while eliminating interference from technique. Since cupping uses high-temperature immersion extraction, the grind size should be neither too coarse nor too fine. When Front Street Coffee conducts cupping, the grind size used is a No. 20 sieve pass rate of 70-75%. Since cupping can rely on a standard sieve to calibrate grind size, other brewing methods can also use the sieve to determine grind size (except espresso).

Suitable grind coarseness for French press: No. 20 sieve pass rate 68-75%

The extraction logic of the French press is very close to cupping, both primarily based on immersion, so the grind size chosen is highly consistent with cupping. In addition, the French press uses a metal filter, and the mesh gaps are visible to the naked eye, so choosing coarser particles also ensures smoother filtration. Grind size should also be adjusted according to different roast levels: Front Street Coffee recommends medium grind for medium-light roasted (with acidity) coffee beans, with a pass rate of 72-75%; medium-coarse grind for medium-dark roasted (less acidic) coffee beans, with a pass rate of 68-71%.

Suitable grind coarseness for pour-over coffee: No. 20 sieve pass rate 70-80%

Pour-over is mainly drip extraction. Unlike long immersion, prolonged soaking tends to bring out undesirable flavors. Pour-over brewing time is shorter, usually between 1 minute 30 seconds and 2 minutes 30 seconds, so the grind size needs to be finer than for cupping to fully reveal the coffee's flavor layers. Front Street Coffee recommends medium-fine grind for medium-light roasted (with acidity) beans, with a pass rate of 75-80%; medium grind for medium-dark roasted (less acidic) beans, with a pass rate of 70-75%.

Suitable grind coarseness for cold brew/ice drip: No. 20 sieve pass rate 75-80%

Unlike pour-over and French press, cold brew and ice drip use low-temperature immersion extraction. In a low-temperature environment, bitter substances are extracted less, and by extending extraction time and allowing the coffee grounds to fully saturate, it is easier to extract small-molecule flavor compounds like floral and fruity notes. But also because of the long extraction time, if the grind is too fine, cold brew coffee will become cloudy and prone to woody flavors, while ice drip may experience water pooling or clogging in the powder layer. Front Street Coffee recommends medium-fine grind for both medium-light and medium-dark roasted beans, with a pass rate of 80-85%.

Suitable grind coarseness for espresso machines (too fine to calibrate with a sieve)

Front Street Coffee's stores dial in espresso every day before opening, and a large part of that work is adjusting grind size. Espresso machines are extremely sensitive to coffee grind coarseness—sometimes a difference of just 0.1 notch on the scale will noticeably change extraction time and flavor. Taking Front Street Coffee as an example, the espresso recipe is 20g of coffee powder extracting 40g of coffee liquid within 28 seconds, with an error controlled at ±1. First fix the extraction recipe, then adjust grind size to achieve this goal, and finally decide based on the tasted flavor whether other parameters need fine-tuning.

Professional coffee knowledge exchange. For more coffee bean information, please follow Coffee Workshop (WeChat public account: cafe_style)

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