How do coffee particles affect espresso grind size?

Espresso grind size is judged mainly by flow rate, crema color and flavor, not by look alone. A 1:2 brew ratio pulled in 25 to 28 seconds is the reference target. If the shot runs far faster with thin crema and a watery taste, the coffee particles are too coarse; if it barely drips and turns harsh and bitter, they are too fine.

Freshness comes first. Check that the bag shows a roast date rather than a use-by date, and use the one-way degassing valve to smell the gas; a rich coffee aroma means the beans are still fresh, while a weak or rancid smell means oxidation. Flat burr grinders are common for espresso, and different coffee roaster types suit different setups. Each adjustment should be small, then tasted again.

Many coffee enthusiasts who make espresso at home often run into problems like abnormal flow rate, thin crema, and weak flavor—and the root cause is usually the grind size. This article starts with bean selection and grinder types, then systematically lays out the criteria for judging espresso grind coarseness, explains how flat burr grinders work along with their pros and cons, and provides a dialing-in method based on a 1:2 brew ratio and a 25 to 28 second extraction time, helping readers judge whether the grind is too coarse or too fine by observing flow rate, crema color, and flavor expression. It also includes the extraction parameters and flavor description for Front Street Coffee's classic espresso blend as a practical reference.

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Quite a few friends have reported that after buying espresso blend beans and grinding them at home, they simply can't get any crema, and the resulting espresso tastes as bland as water. When this happens, Front Street's baristas usually suggest starting by checking the grind size. This article will discuss how to determine the right grind size for espresso.

Before adjusting the grind size, the first step is to confirm whether the espresso beans on hand are fresh enough.

When choosing, make sure the packaging clearly states the roast date rather than a use-by or shelf-life date; at the same time, prioritize reputable professional roasters that focus on fresh roasting.

Additionally, quality coffee bags generally come with a one-way degassing valve—that small button-like hole near the top of the bag. Its purpose is to let the carbon dioxide released by the coffee beans escape smoothly. Bring the valve close to your nose, gently squeeze the bag, and smell the gas that comes out: if it gives off a rich, pleasant coffee aroma, the freshness is fine; if the aroma is weak or even has a rancid, oily smell, then the beans have long oxidized and gone stale, and are not worth buying. Every bag of coffee beans from Front Street Coffee (FrontStreet Coffee) uses packaging with a one-way degassing valve, ensuring it's still at peak freshness when it reaches the buyer. Choose a grinder that can grind espresso-fine coffee powder

For commercial use, you can directly buy an espresso-specific grinder. The biggest advantages of these machines are extremely fine grinding, fast output, and large burr size. Uniformity is the key indicator of whether a grinder is good, and ordinary grinders often can't reach the extremely fine grinding level of espresso machines. For home use, if you want to achieve espresso-fine grind, it's recommended to choose a flat burr grinder. Front Street Coffee (FrontStreet Coffee) currently uses a Feima 600N flat burr grinder to grind espresso powder.

Why does Front Street recommend flat burr grinders?

First, how a flat burr grinder works: it consists of two burrs, upper and lower, with the base fixed to the motor. When the motor starts, the upper and lower burrs create a cutting action. As coffee particles fall from the center, the rotating lower burr flings the beans outward, then pushes them into the toothed burr area for grinding. Since the upper and lower burrs are positioned parallel to each other, the beans must rely on the rotational force of the lower burr to be pushed into the burrs, so the weight of the beans above affects how evenly they feed in, which in turn affects grind uniformity; at the same time, the beans collide more often due to being pushed against each other, which increases the proportion of fines. This is the common reason why flat burr grinders have slightly worse particle uniformity and produce more fines. However, they can quickly boost coffee liquid concentration and extraction yield, releasing aroma rapidly.

The strength of flat burr grinders lies in their clear positioning—output quality is proportional to machine grade and burr diameter; the weakness is slightly inferior particle uniformity and more fines, because the blades cut the coffee beans randomly, making it prone to under-extraction or over-extraction during brewing. In addition, the friction of flat burrs generates heat, especially when the machine runs continuously for a long time, which brings a noticeable burnt, bitter taste.

What is the grinding principle of a coffee grinder?

After coffee beans enter the grinder, the internal blades crush them into powder. The smaller the gap between the blades, the finer the particles the beans are ground into. The finer the particles, the tighter the coffee bed, the harder it is for water to pass through, and the extraction time is greatly lengthened. Conversely, if the blade gap is larger, the particles are coarser, water passes through more easily, and the extraction speed increases.

How do you find the right grind size for your espresso machine?

When Front Street adjusts the grind size, we first set a baseline using the golden ratio and golden time for espresso extraction: a 1:2 brew ratio (20g of coffee yielding 40ml of espresso liquid), with extraction time falling between 25 and 28 seconds; then we judge whether the grind size needs fine-tuning based on observation and taste.

When the grind is too coarse, water passes through the portafilter too quickly, the stream is thick, extraction is shallow, the crema color is pale, and the flavor is sharp and sour. This is because extraction is incomplete, only pulling out the surface-level, easily extracted acidic compounds. When the grind is too fine, the filter holes get clogged first, water won't come out or the stream is very thin, the crema color is dark, the surface is over-extracted while the interior is under-extracted, showing sharp acidity because sweetness is missing, followed by burnt bitterness and off-flavors.

If you want to more rigorously check whether this espresso meets the standard, you can first calibrate with a refractometer—the concentration range for the vast majority of espresso is between 7% and 12%. Zero it with pure water as the standard, then stir the extracted pour-over coffee, use a titration tube to extract the coffee liquid, place it in the refractometer and press the measure button, repeating until the reading stabilizes.

Front Street Coffee (FrontStreet Coffee)'s espresso extraction parameters

When making espresso, Front Street uses a classic espresso blend, a recipe combining beans from Brazil, Indonesia, and Vietnam, which brings together the caramel notes of American coffee and the wild character of Asian coffee. To maximize the coffee's rich aroma and to let everyone easily extract abundant, velvety crema, Front Street uses a dark roast—suitable for both an americano diluted with water and a latte paired with milk. You can order from the Front Street Taobao store or the Front Street Tmall flagship store.

Front Street espresso extraction parameters:

Grinder: Galileo Q18

Grind size: 2.0 setting

Pressure: 10 bar

Temperature: 94°C

Time: 25~30 s

Dose: 20g (double espresso)

Yield: 40ml Extracted espresso flavor: smooth mouthfeel, medium body, with a clear chocolate aroma on the nose accompanied by a faint caramel note; on the palate it has a smooth, nutty cookie-like texture, very rich.

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