What is the Grind Size for Espresso? Reference Guide for Espresso Machine Extraction Grind Sizes

Understanding Coffee Grind Size

Coffee grind size is a factor that can be quite challenging to master. Many problems encountered during brewing stem from inaccurate control of grind size. For pour-over coffee, FrontStreet Coffee recommends calibrating with a #20 (0.85mm) standard sieve, with an 80% pass-through rate (using 10g of coffee grounds, with 8g passing through) as the ideal grind size for pour-over coffee.

However, espresso grind size is extremely fine, making sieve calibration impractical. So how is espresso grind size determined?

Espresso Grind Fineness

If you visit a coffee shop, you'll notice that they typically have at least two grinders: one with a full hopper for espresso, and another for pour-over coffee. Why two separate grinders? The reason is that espresso extraction is extremely sensitive to the fineness of the coffee grounds. Even minute changes in grind size that are invisible to the naked eye will immediately show differences when extracted through an espresso machine.

Therefore, to maintain consistent espresso quality, a dedicated grinder is typically used exclusively for grinding espresso beans. Espresso grounds, whether in appearance or touch, feel like flour. To express this in data, their particle size ranges between 150-300 microns.

How to Determine Espresso Grind Size

According to the definition of espresso by the Italian Coffee Institute and WBC, a standard espresso is defined as 1 ounce (approximately 30ml) of concentrated coffee with golden crema, extracted with hot water at 90.5-96°C under 9 atmospheres of pressure within 20-30 seconds.

Although the above description doesn't explicitly specify the exact grind size, we can easily determine the appropriate grind size by understanding the relationship between extraction time and grind size.

Assuming that human factors such as distribution and tamping are not problematic, the finer the coffee particles are ground, the longer the extraction time becomes, resulting in bitter and burnt flavors, which can easily lead to over-extraction. Conversely, coarser particles result in shorter extraction times, producing more acidic flavors and potentially causing under-extraction.

Therefore, when FrontStreet Coffee faces an unfamiliar espresso bean or has changed to a new grinder, the approach to determining the grind size is as follows: First, establish the extraction recipe. FrontStreet Coffee's preset espresso extraction recipe uses 20g of coffee grounds (depending on the basket capacity) with a 1:2 coffee-to-liquid ratio. FrontStreet Coffee uses the Sunflower Warm Blend, which is roasted slightly lighter than typical espresso beans, so the 1:2 ratio helps highlight the flavor characteristics of the sherry and red cherry coffees. This yields 40g of liquid coffee (using weight measurements because they are more precise than volume measurements, as coffee crema weighs less than its volume).

For pressure and water temperature, fixed parameters are used. FrontStreet Coffee's machine pressure is set at 9 bar, with water temperature at 93°C. With these variables fixed, we only need to adjust the grind size to reach the preset time range. Some grinders have hoppers, so after each adjustment, the remaining grounds need to be cleaned out to avoid affecting the accuracy of subsequent adjustments.

When the extraction falls within our preset time range, don't get too excited yet. What we want is a delicious espresso, so this is when tasting comes in. We need to determine if there are any defective flavors such as bitterness, sharp acidity, or watery textures. Secondly, we assess whether the characteristic flavors of this particular coffee are present. If not, further adjustments are needed, and these adjustments are no longer limited to just grind size. This is because our preset brewing parameters are based on existing knowledge, and when facing an unfamiliar coffee bean, we must consider whether our preset extraction parameters are reasonable.

For example, when FrontStreet Coffee was testing a Colombian SOE coffee, after adjusting to the appropriate grind size, the extraction parameters were 20g of coffee grounds yielding 40g of liquid coffee in 26 seconds. However, a slight bitterness was detected during tasting. Through segmented testing, it was found that the bitterness came from the tail end of the extraction, so the extraction ratio was adjusted to 20g of coffee grounds yielding 35g of liquid coffee, with a time of 24 seconds.

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