Espresso Grind Size Characteristics and Calibration: Reference Values for Coffee Machine Grind Settings

The Importance of Grind Size in Coffee Extraction

Regardless of which extraction method is used for coffee, finding the right grind size is a crucial step. The coarseness of the grind directly affects extraction stability and flavor expression. Espresso, being extracted under high temperature and pressure, demands even finer precision in coffee grinding.

The Principles of Espresso Extraction

Before espresso emerged, coffee was brewed through immersion methods, requiring slow extraction that meant waiting several minutes for a single cup. Espresso was invented in the early 19th century when Italians conceived of using steam pressure to force high-temperature, high-pressure water through a coffee puck to accelerate the traditional drip extraction rate. Through continuous improvements and innovations, this led to the semi-automatic and fully automatic espresso machines commonly seen today.

When using an espresso machine for extraction, soluble flavor compounds must be released into hot water within mere tens of seconds. This requires more thorough contact between coffee and water, meaning the grind must be extremely fine and uniform. Because espresso uses pressurized, short-time extraction, it also means it amplifies all characteristics—positive flavors are enhanced, but so are defects. This makes the requirements for grinding even more demanding.

Grind Size Requirements for Espresso Machines

If a coffee shop's menu includes both espresso and pour-over coffee, it will typically have at least two different grinders. The grinder used for espresso produces coffee powder as fine as powdered sugar, with particle size between 150-300 microns. The coarseness and uniformity cannot be observed with the naked eye, but we can determine the correct grind size by observing the coffee-water extraction state.

If the grind is slightly too fine, water passes through the coffee bed more slowly, leading to over-extraction. If the grind is slightly too coarse, water passes through the coffee bed too easily, causing under-extraction. Such deviations might result from a difference of just 0.1 grind settings. Therefore, we typically observe the flow rate and taste the espresso during brewing to determine if it's within the appropriate range and make adjustments accordingly.

How to Adjust Espresso Grind Size in Daily Practice

When we get a new bag of coffee beans and want to brew delicious coffee, the first thing to do is determine the grind size. If we haven't used our grinding equipment before and don't know how to determine the appropriate setting range, we can start by testing small amounts of coffee beans at different setting intervals. When the ground coffee feels like flour to the touch, you can feel it with your hand—soft and without roughness.

At this point, we can apply the common espresso formula for extraction. FrontStreet Coffee suggests using a liquid-to-coffee ratio of 1:2, meaning extracting about 2 grams of coffee liquid from 1 gram of coffee grounds, with a time between 20-30 seconds. For example, FrontStreet Coffee uses a 20-gram portafilter basket, meaning 20 grams of coffee grounds to extract 40 grams of coffee liquid. If the time is less than 20 seconds, the flow rate is too fast; when extraction exceeds 30 seconds, the flow rate is too slow. Fast flow means water spends too little time passing through the coffee grounds, and the coffee often tastes weak or overly acidic, requiring a finer grind. Similarly, too slow flow indicates the coffee is ground too finely, making it difficult for water to pass through the coffee bed, and the coffee easily becomes bitter, requiring a coarser grind.

Adjusting grind settings typically relies on accumulated daily experience. If you're within 5 seconds of the target time, you can adjust by 0.2 settings each time. If the time difference is too large, you can be bolder, adjusting by 0.5-1 settings. Even if you go from extraction time being too long to too short, you can lock in this grind setting range and gradually fine-tune to the target value.

The formula mentioned above by FrontStreet Coffee is just to help us quickly find the appropriate grinding range—it doesn't necessarily mean the extracted espresso will taste good. Ultimately, we still need to consider the coffee beans' characteristics and flavor, using our experience to determine whether the extraction is qualified. If you're a barista, FrontStreet Coffee believes you'll quickly grasp the patterns through multiple practical sessions at the café. If you're just making coffee at home during leisure time, you may need long-term learning and accumulation, with more recording and summarizing, which will help us more quickly adjust to brew delicious coffee.

If the espresso has a noticeable burnt, bitter taste but moderate concentration, it might be due to excessive extraction time releasing too many bitter compounds. You can slightly adjust the grind to be coarser. If the crema layer on top of the coffee liquid appears pale and thin, it might be due to excessive tail-end extraction. You can reduce the coffee liquid weight, meaning extract less, and suggest increasing the coffee-to-liquid ratio to between 1:1.5-1:1.7. When the espresso flavor is rich but the aftertaste is short, you can appropriately extract more coffee liquid, trying to adjust the ratio to 1:2.5.

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