Does Grind Size and Bean Resting Change How Long a Moka Pot Takes?

Grind size is the variable that shapes pour-over extraction most, because it sets both the contact area between water and grounds and how long the water takes to pass through the bed. A finer grind extracts faster and can turn bitter or harsh, while a coarser grind slows extraction and can leave the cup thin and sour.

Start by confirming the roast date on the bag. Beans need roughly 3 to 7 days to degas, and the usual resting window is 3 to 4 days for medium-light roasts and 4 to 5 days for medium-dark roasts. Freshly roasted espresso coffee beans still releasing carbon dioxide make extraction unstable until that rest is complete.

Grind size is the core variable you can't avoid in pour-over coffee. It simultaneously affects the contact area between water and coffee grounds and the extraction rhythm, which in turn determines the flavor direction in the cup. This article starts with coffee bean freshness and resting, explains the difference in extraction yield between fine and coarse grounds, and describes the corresponding taste performance when the grind is too fine or too coarse. It also introduces the method of calibrating grind with a 0.85mm cupping sieve, as well as Front Street Coffee's reference table of applicable equipment organized by five levels—extra fine, fine, medium-fine, medium, and coarse—to help you find the right grinding range across different roast levels and brewing tools.

Whether coffee is ground coarse or fine changes the contact area between water and coffee particles and also changes how long extraction lasts, all of which ultimately shows up in the cup. Yet grind size is precisely the part that leaves people most unsure. Below, Front Street Coffee will talk about how to determine the grind size for different coffee beans.

Step one: first confirm whether the single-origin beans or espresso blend beans in your hands are freshly roasted.

When buying single-origin coffee beans or espresso coffee beans, the packaging should ideally have both a one-way degassing valve and a clear roast date. That button-like "one-way degassing valve" on the upper part of the bag allows the carbon dioxide released by the beans to escape while preventing outside gas from flowing back into the packaging. Every bag of coffee beans produced by Front Street Coffee is freshly roasted and comes in packaging equipped with a one-way degassing valve.

After receiving the beans, first check the roast date. During roasting, the bean body accumulates a large amount of carbon dioxide, so it needs 3 to 7 days to degas on its own, which is commonly called resting. If beans that were just roasted are brewed immediately, the carbon dioxide continuously escaping during brewing will make the entire extraction very unstable. As for how long to rest them, Front Street Coffee's recommendation is: 3 to 4 days for medium-light roasts, and 4 to 5 days for medium-dark roasts.

As mentioned earlier, the most intuitive sign of whether beans are fresh is carbon dioxide release. In addition, freshness also determines how many aromatic substances remain, which flavor and aroma depend on. These smaller aromatic molecules volatilize more easily than the larger molecules that bring bitterness; the longer the beans are stored, the more carbon dioxide and aromatic substances are lost, and naturally the less there is to extract. Once beans are not fresh, no amount of grind adjustment can save them.

How exactly does grind size influence flavor?

1. At the same weight, the finer the grind, the more times the coffee grounds are cut, the larger the total surface area, and the greater the range that water can contact the coffee grounds.

2. The finer the grind, the smaller the particles, the shorter the distance for water to penetrate from the particle surface to the center, and the shorter and easier the time needed to extract the flavor substances inside.

To put it plainly: when other conditions remain unchanged, the finer the particles, the higher the extraction yield—when the grind is fine, the contact surface with water is larger, and the dissolved concentration is higher; conversely, when the grind is coarse, the contact surface area is smaller, and the extracted concentration is lower.

What happens if the grind is too fine?

Visually, the particles are smaller; and precisely because the particles are small, the gaps between them are narrower, making it harder for water to pass through, so the drip time is prolonged. A fine grind means the particle surface area becomes larger, there are more sites available for water to extract, and both concentration and extraction yield rise together. It tastes rich, with prominent bitterness and astringency, while other flavors are suppressed instead.

What happens if the grind is too coarse?

Visually, the particles are larger; when the particles are large, the spacing between them is wider, water passes through the coffee bed more easily, and the filtration time shortens accordingly. A coarse grind means the particle surface area is reduced, there are fewer extraction sites, and both concentration and extraction yield decline. It tastes weak, with a light mouthfeel, and the flavors are almost impossible to capture.

So how exactly should grind size be determined?

Front Street Coffee recommends using a cupping calibration sieve No. 20 (0.85mm mesh) to judge. Take 10g of coffee beans, grind them roughly, pour them into the sieve and sift; after sifting, see how much powder has fallen into the tray, and use the pass-through rate to calibrate the grind. Front Street Coffee's grind-size standard sieve pass-through rates are: cold brew > pour-over, siphon 80% > moka, American drip 75-80% > cupping 70-75% > French press 65-70%.

Of course, different roast levels require corresponding changes in grind size. For example, when Front Street Coffee brews light-roast beans, it uses a grind with a 0.85mm sieve pass-through rate of 80-85%; for medium-roast beans, a grind with a pass-through rate of 70%-75%; and for dark-roast beans, a grind with a pass-through rate of 65%-70%. However, everyone's preference for strength differs, so these numbers are only for reference, and in practice you can still fine-tune according to your own taste preference.

What if you don't want to buy a grind calibration sieve?

Front Street Coffee also knows this whole process is quite troublesome, so it has made a simple summary of common grind sizes for easy comparison with your brewing equipment. Front Street Coffee divides coffee ground size into five levels: extra fine, fine, medium-fine, medium, and coarse.

(From left to right: coarse, fine, extra fine)

Extra fine: used for espresso (moka pot, espresso machine).

When making espresso, be sure to tamp the coffee grounds firmly so they create resistance to the high-pressure hot water, allowing the essence of the coffee to be extracted. The more uniform and delicate the grind, the more compact the puck after tamping, and the more balanced the resistance to water flow, so that the espresso "pressed" out this way has a rich crema.

Fine: used for drip bag coffee.

This grind size is Front Street Coffee's "soul partner" for making drip bags. The entire drip bag is made of filter paper, and water flows out very quickly, unlike a pour-over dripper with a narrowed structure—for example, the commonly used three-hole dripper is actually slowing down the water flow. Therefore, drip bags need a fine grind even more to expand the extraction area and extract more substances.

Medium-fine: used for medium-light roast coffee (various pour-over drippers).

When brewing medium-light roast beans, Front Street Coffee uses medium-fine grind, roughly the size of fine granulated sugar, with a sieve pass-through rate between 75%-80%. Medium-light roast beans usually have abundant acidity, and medium-fine grinding can enhance the overall sweet-and-sour performance.

Medium: used for medium-dark roast coffee (various pour-over drippers).

When brewing medium-dark roast beans, Front Street Coffee uses medium grind, roughly the size of coarse granulated sugar, with a sieve pass-through rate between 70%-75%. Medium grind is less likely to produce very fine powder, and less likely to cause a large amount of water to accumulate and soak the coffee bed due to unstable water flow at the beginning of pouring, thereby avoiding over-extraction.

Coarse: used for French press.

The French press relies on a 4-minute steep to extract the truest flavor of the coffee. Compared with pour-over, its coffee liquid will be somewhat cloudy because the metal filter mesh has a larger pore size. There are two reasons for choosing a coarse grind: first, to let the flavor release slowly; second, so that when the filter is pressed down, the coffee grounds will not "slip" through the gaps into the coffee and affect the mouthfeel.

To learn more about specialty coffee beans, you can add the private WeChat of Front Street Coffee, WeChat ID: kaixinguoguo0925

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