How Does Moka Pot Coffee Grind Size Affect Extraction?

Grind size decides how a coffee tastes, yet grinder scale numbers are not standardized, so the same setting can mean different coarseness on different machines. A Chinese Standard No. 20 sieve with 0.85 mm apertures measures this directly: you shake a sample through it and weigh the proportion that passes, giving a repeatable grind figure independent of any brand's scale.

Finer grinds cut the beans more, exposing greater surface area to water and raising extraction; coarser grinds lower concentration, thin the body and push acidity forward. Each brewer needs its own pass-through range, so the article lists reference figures for pour-over, French press, cold brew, espresso and moka pots across roast levels.

Grind size is the key variable that determines the direction of coffee flavor, but the scales on grinders on the market are all over the place, and the same number may correspond to wildly different coarseness levels on different devices. How fine is fine, exactly? And how do you judge the size of granulated sugar? This article starts from the impact of grind size on extraction, systematically introduces how to use the Chinese Standard No. 20 0.85mm aperture sieve to quantify coffee powder coarseness, and for common brewing methods such as pour-over, French press, cold brew, espresso machines, and moka pots, provides reference ranges for grind pass-through rates under different roast levels along with comparison methods, to help you find the grind parameters that suit your own equipment.

"How fine should pour-over coffee really be ground?" "Why does the same scale number produce completely different results from your grinder and mine?" "When people say granulated sugar consistency, do they mean fine granulated sugar, coarse granulated sugar, or yellow granulated sugar?"... If you've ever been troubled by these questions, then this article is for you. Front Street is going to help you figure out once and for all how to determine coffee grind coarseness! (Bookmark this! Bookmark it! BOOKMARK IT!!)

How important is coffee grind size?

Given the same weight of coffee beans, the finer the grind, the more times the coffee particles are cut, the greater the total surface area, and the more coffee powder surface water can contact. Conversely, the coarser the grind, the lower the coffee's concentration and extraction yield, the weaker the body, and the more prominent the acidity.

Because different coffee brewing devices have different extraction principles, their grind size requirements also vary, and the scales on grinders have no industry-wide standard. Therefore, we need a reliable testing tool—the Chinese Standard No. 20 0.85mm aperture sieve, also called the coffee bean grind size cupping calibration sieve, which Front Street usually abbreviates as the coffee powder sieving mesh.

How do you use a coffee powder sieve to determine grind coarseness?

Those reading carefully might ask: why the cupping calibration sieve specifically? Although there are many types of brewing devices on the market and everyone has their own insights on brewing parameters, in the coffee industry, cupping is the universally recognized benchmark. Initially cupping was used to evaluate green bean quality, but later people also gradually used cupping to judge coffee flavor and thereby determine suitable brewing parameters for a sample. And the grind size used in cupping is a No. 20 sieve pass-through rate of 70-75%.

The method is simple: when Front Street determines grind size, we first take 10g of coffee beans and grind them, then pour the grounds into the middle sieve layer, cover with the lid, and shake horizontally until no more coffee particles fall into the lower collection bowl. Then we weigh the coffee powder that passed through the sieve—that weight is the pass-through rate. In other words, if 7g to 7.5g out of 10g of coffee powder passes through the sieve, the grind size meets the standard of a No. 20 sieve pass-through rate of 70-75%. The finer the coffee powder, the higher the pass-through rate; the coarser, the lower the pass-through rate.

Grind Size Standards & Reference Charts for Common Brewing Devices

Drip extraction / pour-over coffee grind size (No. 20 sieve pass-through rate 68-80%)

Suitable for v60, kono, ice pupil, origami dripper, fan-shaped dripper, cake dripper, clever cup, American drip machine

Drip brewing is pour-over coffee: the principle is that water passes through the coffee bed to extract flavor compounds, then is filtered through paper to obtain a clear coffee liquid. Generally speaking, pour-over brewing time is on the shorter side, so the grind size needs to be somewhat finer.

Coffee beans of different roast levels also have different grind size requirements. Front Street's recommendation is: for medium-light to medium roast beans, the grind size corresponds to a No. 20 sieve pass-through rate of 75-80%; for medium-dark roast beans, the grind size corresponds to a No. 20 sieve pass-through rate of 70-75%.

(75-80% pass-through rate coarseness)

(70-75% pass-through rate coarseness)

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

The French press extracts coffee through immersion, with a longer steep time (about 4 minutes), and its filter mesh is also denser, so the grind size needs to be coarser. This reduces the risk of over-extraction and also allows for better filtration of coffee particles.

Coffee beans of different roast levels likewise require grind size adjustments. Front Street recommends: for medium-light to medium roast beans, the grind size is a No. 20 sieve pass-through rate of 70-75%; for medium-dark roast beans, the grind size is a No. 20 sieve pass-through rate of 65-70%.

(70-75% pass-through rate coarseness)

(65-70% pass-through rate coarseness)

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

Low-temperature extraction is completely different from high-temperature extraction. In an ice-water mixture or refrigerated environment, coffee extraction efficiency is extremely low, the release rate of flavor compounds is greatly slowed, and the production cycle is quite long. The advantage of low-temperature extraction is that it can fully extract sweet and acidic compounds while reducing the precipitation of bitter compounds.

Because extraction is slow, the grind size can be somewhat finer, but not too fine. Front Street recommends that when making cold brew or ice drip, the coffee bean grind size should be a No. 20 sieve pass-through rate of 80-85%. For a richer mouthfeel, choose 85% pass-through rate; for a lighter, more refreshing taste, choose 80% pass-through rate.

(80-85% pass-through rate coarseness)

Pressurized extraction / espresso machine grind size (grind size cannot be determined with No. 20 sieve)

The grind size used by espresso machines is extremely fine, smaller than the 0.85mm aperture, so it cannot be determined by sieving through a No. 20 sieve. Just how fine it is—refer to the image below.

(espresso grind coarseness)

To determine espresso grind size, you need repeated extraction and tasting to adjust. Front Street's espresso extraction recipe is: 20g of coffee powder extracted into 40g of coffee liquid within 28 seconds (tolerance ±1). You can refer to this recipe and then fine-tune based on the flavor performance of the espresso.

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

The moka pot is similar—the grind size used is also very fine, but slightly coarser than espresso machines. However, it is still smaller than the 0.85mm aperture, so it likewise cannot be determined by sieving through a No. 20 sieve.

Whether the grind size is appropriate can be judged by referring to the gap size of the moka pot's filter basket—just make sure the coffee particles won't pass through the gaps. For details, refer to the image below.

(moka pot grind reference)

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