How does grind size change pour-over extraction?

Grind size sets the contact area between water and grounds, which controls extraction time and the taste in the cup. Too fine a grind over-extracts and turns bitter or harsh; too coarse a grind under-extracts and tastes weak or sour. The article explains how a 0.85mm sieve calibrates pass-through rate and gives grind ranges for different roast levels.

Five levels are covered: extra fine, fine, medium-fine, medium, and coarse, so each brewing device can be matched quickly. Before dialing in, confirm the beans are freshly roasted and rested, since carbon dioxide released during roasting disturbs extraction. The guidance suggests resting 3 to 4 days for medium-light roast and 4 to 5 days for medium-dark, whether the target is pour-over or a grind setting moka pot.

Grind size is one of the most critical variables in pour-over coffee—it determines the contact area between water and coffee grounds, and also influences extraction time and the final flavor. This article will systematically sort out the logical relationship between grind size and extraction yield, tell you what kind of taste will appear in the cup when the grind is too fine or too coarse, and also introduce how to use a 0.85mm sieve to calibrate the pass-through rate, with specific grinding recommendations for beans of different roast levels. If you do not want to buy an extra sieve, the article also categorizes five levels—extra fine, fine, medium-fine, medium, and coarse—so you can quickly find the right setting for your brewing device.

For more specialty coffee knowledge, please follow: Front Street Coffee (Frontsteet Coffee) Whether coffee grounds are ground coarse or fine directly affects how much surface area of the grounds the water can touch, and also affects how long the extraction process lasts, all of which ultimately shows up in the taste in the cup. Yet setting the grind size is precisely the step that puzzles the most people. Next, Front Street will talk about how grind size should actually be determined for different coffee beans. The first step is to confirm that the single-origin beans or espresso blend beans in your hands are freshly roasted. When purchasing, check whether the packaging has a one-way exhaust valve and whether the roast date is marked. That small button-shaped hole at the top of the bag is the one-way exhaust valve. Its function is to let coffee beans release naturally produced carbon dioxide while keeping outside air out of the bag. Every bag of beans produced by Front Street Coffee (FrontStreet Coffee) uses fresh roasting plus one-way exhaust valve packaging.

After receiving the beans, you can check the roast date. During roasting, the beans accumulate a large amount of carbon dioxide, so they need 3 to 7 days to release it on their own, which is commonly called resting the beans. If you skip resting and directly brew just-roasted beans, the continuously escaping carbon dioxide will seriously interfere with the extraction rhythm and make the entire brewing process very unstable. So how long should they rest? Front Street's recommendation is: rest 3 to 4 days for medium-light roast, and 4 to 5 days for medium-dark roast.

As mentioned earlier, the freshness of beans is most intuitively reflected in carbon dioxide release. But besides carbon dioxide, freshness also determines the aromatic substances on which coffee flavor and aroma depend. These small-molecule aromatics are more volatile than the large-molecule substances that bring bitterness, so the less fresh the beans are, the less carbon dioxide and aromatics they have, and naturally the less there is that can be extracted. Once the beans are no longer fresh, no amount of grind adjustment can save them. How does grind size influence coffee flavor? 1. At the same weight, the finer the grind, the more times the coffee grounds are cut, the larger the total surface area becomes, and the more ground surface area the water can contact. 2. The finer the grind, the smaller the particles are cut, the shorter the distance from the particle surface to the particle center for water to travel, and the shorter the time needed for water to penetrate into the particle interior to complete extraction, making flavor substances easier to extract.

Simply put, when other conditions remain unchanged, the finer the particles, the higher the extraction yield. When the grounds are finely ground, the area contacting water is large, and the dissolved concentration is high; when the grounds are coarsely ground, the surface area contacting water is small, and the extracted concentration is low. What happens when the grind is too fine? Visually, the particles are smaller, and the gaps between particles are narrower, so water does not easily penetrate. As a result, during brewing the drip rate becomes slower and takes longer. Fine grinding expands the surface area of the grounds, increases the places where water can extract substances, and both concentration and extraction yield rise. It tastes intense, with prominent bitterness and astringency, while other flavors are suppressed.

What happens when the grind is too coarse? Visually, the particles are obviously larger, and the spacing between particles is wider, so water passes through the coffee bed easily, filtration is faster, and the time is shorter. Coarse grinding reduces the surface area of the grounds, decreases the places available for water to extract, and concentration and extraction yield decline accordingly. The coffee tastes thin and bland, with a light mouthfeel, and almost no flavor can be sensed.

So how do you determine grind size? Front Street recommends using a No. 20 sieve (0.85mm mesh) for calibration. Take 10g of coffee beans, grind them roughly, pour them into the sieve, sift thoroughly, observe how much ground coffee has fallen into the tray, and then adjust the grind size according to the pass-through rate. Front Street Coffee's (FrontStreet Coffee) grind coarseness standard sieve pass-through rates are as follows: cold brew > pour-over, siphon 80% > moka pot, American drip 75-80% > cupping 70-75% > French press 65-70%.

Of course, beans with different roast levels also require corresponding changes in grind size. For example, when Front Street brews light-roast beans, it uses a grind with an 0.85mm sieve pass-through rate of 80-85%; for medium-roast beans, it uses a grind with a pass-through rate of 70%-75%; and for dark-roast beans, it uses a grind with a pass-through rate of 65%-70%. However, everyone's preference for strength differs, so these values are for reference only, and you can absolutely fine-tune them according to your own taste. What if you do not want to buy a grind calibration sieve? Front Street understands that this whole process is indeed cumbersome, so it has put together a small comparison guide for coffee ground size, making it easy for everyone to find an approximate setting based on the brewing tool at hand. Front Street divides coffee ground coarseness into five levels: extra fine, fine, medium-fine, medium, and coarse.

(From left to right: coarse, fine, extra fine) Extra fine: used for espresso coffee (moka pot, espresso machine). When making espresso, be sure to tamp the coffee grounds firmly so that they create resistance to the high-pressure hot water and the essence can be extracted. The more uniform and delicate the grind, the more compact the puck after tamping, and the more even the resistance to water flow. Only then does the espresso pressed out this way have a rich crema.

Fine: used for drip bag coffee. This coarseness is Front Street's "soul partner" for making drip bags. Drip bags are entirely made of filter paper, and water flows out very quickly. Unlike pour-over, they do not have a narrowed structure—for example, the common three-hole dripper plays a role in slowing the water flow—so drip bags need finer grounds to expand the extraction area and thus dissolve more substances.

Medium-fine: used for brewing medium-light roast coffee (various pour-over drippers). Recommended: Front Street Guodingding, Front Street Huakui, Front Street Geisha, Front Street Strawberry Candy. When Front Street brews medium-light roast beans, it uses medium-fine grounds, roughly the size of fine granulated sugar, with a sieve pass-through rate between 75%-80%. Medium-light roast beans usually have rich acidity, and medium-fine grounds can enhance the overall sweet-and-sour performance.

Medium: used for brewing medium-dark roast coffee (various pour-over drippers). Recommended: Front Street Jamaica Blue Mountain, Front Street Golden Mandheling, Front Street Huilan. When Front Street brews medium-dark roast beans, it uses medium grounds, roughly the size of coarse granulated sugar, with a sieve pass-through rate between 70%-75%. Medium grounds are less likely to produce extra fine powder, and are also less likely to cause a large amount of water to accumulate in the dripper and soak the coffee bed because of unstable pouring at the beginning, thereby avoiding over-extraction.

Coarse: used for making coffee with a French press. A French press relies on a four-minute steep to extract the truest flavor of the coffee. Compared with pour-over, French press coffee liquid is more turbid because the metal filter mesh has larger holes. Therefore, the grind size should be coarse: first, the flavor can be released slowly; second, when the filter is pressed down, the coffee grounds will not squeeze out through the gaps and mix into the coffee, affecting the mouthfeel.

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