How Does Grind Size Change the Way an Espresso Machine Works?

Espresso grind size is adjusted by moving the grinder dial in small steps and then pulling a shot to check the flow rate. Espresso grounds should feel finer than fine salt, close to flour. Grinding slightly finer adds resistance and risks over-extraction, while slightly coarser grounds let water pass too fast and cause under-extraction, so the dial is corrected by taste and flow, not by eye.

Because pressurized, short-time extraction magnifies both strengths and flaws, particle size and uniformity matter more than in pour-over or cold brew. A sieve cannot judge espresso grounds, so the practical method is to watch the flow rate and taste each shot, then move the dial a few tenths of a notch at a time until the flavor lands in range.

In the process of making espresso, the coarseness of the grind is one of the core variables that determines the success or failure of extraction. Compared with pour-over or cold brew, espresso grounds are closer to the feel of fine salt or even flour, and a tiny deviation on the dial can cause abnormal flow and push the flavor toward either under-extraction or over-extraction. This article systematically sorts out the logic for setting the grind dial on a semi-automatic espresso machine from the angles of grind assessment, coffee bean selection, flow rate correction, and flavor fine-tuning, and shares Front Street Coffee's adjustment experience in practice, to help you consistently produce an ideal shot of espresso at home.

Most people who make coffee understand that how coarse or fine the grounds are ground directly affects the final taste. As long as the grind size is wrong, or the particle size is uneven, that cup of coffee will most likely fall into the pit of under-extraction or over-extraction. Compared with methods like pour-over and cold brew, espresso demands a much higher degree of grind fineness, and adjustments must also be more precise, so that the flavor of the espresso can land in the ideal range.

How fine should espresso grounds actually be ground?

When talking about pour-over coarseness, Front Street Coffee habitually uses the Chinese No. 20 standard sieve as a reference, checking how much coffee powder passes through a mesh surface with a fixed aperture to judge whether the particle size is appropriate. But espresso follows the path of pressurized, short-time extraction, and all flavor expressions are magnified—the strengths as well as the flaws—so the requirements for grinding are especially strict. Its particles are finer than fine salt, and the coarseness and uniformity cannot be distinguished by the naked eye at all, so measuring with a sieve is also impractical.

If the grounds are ground slightly finer, the resistance of water passing through the coffee bed increases, easily causing over-extraction; conversely, if the grounds are slightly coarser, water passes through too smoothly, leading to under-extraction. And what causes this deviation may be just a difference of a few tenths of a notch. Therefore, in actual operation we usually observe the flow rate and taste of the espresso while extracting, using that to judge whether the current coarseness falls within a suitable range.

Choose the right coffee beans

In fact, when making a cup of espresso, besides getting all the parameters right, Front Street Coffee believes that choosing the right beans is equally key—after all, the beans are the foundation that determines whether this cup of coffee tastes good.

If you want to make espresso at home at coffee shop level, you can try Front Street Coffee Classic Espresso Blend. This bean blends the characteristics of three origins—Brazil, Indonesia, and Vietnam—combining the caramel sweetness of American beans with the wild character of Asian beans. In order to maximize the richness as much as possible and let everyone easily extract a thick, dense crema, Front Street Coffee used a deep roast. Whether diluted with water to make an Americano or added to milk to make a latte, it is quite suitable, and you can order it from the Front Street Coffee Taobao store or the Front Street Coffee Tmall flagship store.

If you prefer espresso with fruity notes, then medium-roast beans should be your main choice. Here we recommend Front Street Coffee Strawberry Candy espresso beans, available directly from the Taobao or Tmall stores. This bean is based on Front Street Coffee Costa Rica Tarrazu, known for its honey processing, paired with Ethiopia, the birthplace of coffee, and then combined with Colombian beans. The resulting espresso is not harsh on the palate, and under machine extraction it has good crema and a dense texture while also bringing out a sweet-and-sour sensation similar to strawberry gummy candy.

How do you first define a suitable grind size range?

When you get a bag of beans you have never worked with before and want to brew a good-tasting cup, the first step is to lock in the grind size. If the grinder has not been used before and you are not sure which notch to start from, you can first use a small amount of beans to test grind in a few different notch ranges. When the grounds feel like flour to the touch, soft and without any granular feel when pinched by hand, it is about right.

Next, you can apply the common espresso formula to extract. Front Street Coffee suggests a coffee-to-liquid ratio of 1:2, that is, 1 gram of coffee yields about 2 grams of coffee liquid, with the time controlled at 25 to 30 seconds. For example, if Front Street Coffee uses a 20-gram capacity portafilter basket, then dose 20 grams of coffee and extract 40 grams of liquid. If the time is under 20 seconds, the flow rate is too fast; if it exceeds 35 seconds, the flow rate is too slow.

A fast flow rate means the time for water to pass through the coffee bed is too short, and the coffee often tastes weak or sour, so the grind needs to be adjusted finer. Adjusting the dial mainly relies on accumulated daily experience. If the gap from the target time is within 5 seconds, you can move 0.2 notch each time; if the gap is relatively large, feel free to be bolder and adjust by 0.5 to 1 notch. Even if it suddenly goes from too long to too short, you can use that to lock in an approximate notch range and then gradually narrow it down. By the same logic, a flow rate that is too slow means the grounds are too fine, water struggles to pass through the coffee bed, and the taste easily becomes bitter, so you need to adjust coarser.

How do you find the truly correct grind setting?

The formula mentioned above by Front Street Coffee is only meant to help everyone quickly define a usable grind range; it does not mean that the espresso extracted this way will necessarily taste good. Ultimately, you still need to combine the characteristics of the beans themselves with the actual taste to judge whether the extraction is qualified.

If the espresso tastes distinctly burnt and bitter, but the strength is still fairly moderate, then it may be that the time is too long and too many bitter substances have been released, so you can adjust the grind slightly coarser. If the crema on top of the coffee liquid is pale in color and thin in texture, it may be that the tail end of extraction has gone too far, so you can reduce the liquid weight, that is, extract less. It is recommended to raise the coffee-to-liquid ratio to between 1:1.5 and 1:1.7. When the espresso has fairly rich flavor but a relatively short finish, then you can extract a little more and try adjusting the ratio to 1:2.5.

In the end, the extraction formula is only a reference. If you are rigidly bound by it, it instead becomes very difficult to dial in good flavor, and in the end you can only repeatedly adjust the grind and waste beans for nothing. The time also does not have to be strictly kept at 25 to 30 seconds; sometimes 36 seconds or 24 seconds is the state in which this bean tastes best. When Front Street Coffee makes coffee, all parameter adjustments are built on daily experience. If your household output is not large and it is relatively hard to grasp, Front Street Coffee suggests recording the parameters and flavor each time, and summarizing more of the correspondence between extraction conditions and taste performance, so that adjustments become faster and some unnecessary loss can be avoided.

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