How to dial in espresso coffee beans by grind size

Espresso reacts to small changes far more than pour-over does, so grind size is the main lever for dialing in a shot. Six variables drive the result: dose, brew ratio, extraction time, flow rate, extraction pressure, and extraction temperature. Adjust grind first, then time the shot and taste.

Start with a consistent dose, distribute and tamp level, then run the shot and watch the flow. If it runs too fast and tastes sour, grind finer; if it chokes and tastes bitter, grind coarser. Keep the same espresso coffee beans between adjustments, and clean the basket and grinder to avoid retained grounds skewing the next shot.

Espresso extraction is far more sensitive than pour-over, and any slight parameter deviation will be multiplied in the flavor. Based on the practical experience of Front Street Coffee, this article systematically sorts out the six core variables affecting espresso extraction—dose, brew ratio, extraction time, flow rate, extraction pressure, and extraction temperature—to help you understand how grind size should be adjusted and judged. At the same time, the article also explains in depth operational details such as weighing the dose, distributing the grounds, tamping, machine extraction, and cleaning, and analyzes easily overlooked issues such as retained grounds and dosing grinder errors. Whether you are a beginner just getting into espresso or an enthusiast hoping for consistent output, you can find practical adjustment ideas here.

Front Street Coffee (FrontStreet Coffee) has always believed that the extraction parameters of pour-over coffee have a decisive impact on the final flavor, and when applied to espresso, this impact is only more pronounced. Espresso is more demanding than pour-over in terms of concentration, extraction time, and other aspects. Even a tiny deviation will be multiplied in the flavor finally presented in the cup. Therefore, truly understanding the various extraction parameters of espresso is quite necessary.

The prerequisite for a delicious cup of coffee is, of course, good beans. Here Front Street first lists several espresso coffee beans suitable for most people, making them easier to choose:

"Front Street Specialty Blend Coffee Beans" 75 yuan/454g: made from a combination of Colombian washed coffee beans and Brazilian semi-washed coffee beans, presenting flavors of nuts, dark chocolate, and caramel.

"Front Street Classic Blend Coffee Beans" 33 yuan/100g: Brazilian semi-washed coffee beans paired with Indonesian Mandheling coffee beans and Vietnamese coffee beans, with rich crema and a mellow mouthfeel;

"Front Street Strawberry Candy Espresso" 43 yuan/100g: selected Costa Rican coffee beans, Panamanian coffee beans, and Ethiopian coffee beans, with aromas of roses, strawberry candy, and glucose, a distinct fruity sweet-and-sour character, and a pleasing taste.

First, like the extraction parameters of pour-over coffee, espresso has even higher requirements for parameter control. The following analysis will be developed separately from the dimensions of dose, brew ratio, extraction time, flow rate, extraction pressure, and extraction temperature.

Dose The dose depends on the capacity of the filter basket. Coffee machine manufacturers usually provide specifications for double filter baskets, such as 16g, 18g, 20g, 22g, and other options. These numbers are recommended capacities, and the allowable filling error should be controlled within 1g. For example, the reasonable dose range for an 18g filter basket can be 17 to 19g.

Front Street does not recommend using a dose that is much less or much more than the filter basket specification. Changes in dose directly affect the density of the coffee puck: under the same tamping force, too little coffee powder will make the puck looser, speed up the water flow, and thus cause underextraction; conversely, too much coffee powder will make the density too high, slow the flow rate, and may even make it difficult to extract coffee liquid.

Brew Ratio Espresso uses the ratio between coffee powder and espresso liquid, because it is impossible to infer exactly how much water participated in the extraction—of course, some new coffee machines install a flow meter at the water inlet to display the water volume. The earliest extraction ratio was the single espresso standard, namely 7 to 8g of coffee powder extracting 25 to 30ml of espresso liquid. The former is a unit of weight, and the latter is a unit of capacity (volume). Only under the premise of consistent density can the two be interchangeable and equivalent. But we know that the surface of the extracted espresso has golden crema, and the thickness of this crema depends on the roast level and freshness, so measuring in this way will lead to inconsistent output.

Thus the ratio method of coffee powder weight to liquid weight appeared, usually falling between 1:1.5 and 1:2.5, with 1:2 being the most common, such as 20g of coffee powder extracting 40g of coffee liquid. This ratio is affected by two factors: dose and water amount. When the ratio is low, the coffee tastes very rich and heavy, and tends to bring out the bitterness caused by overextraction; when the ratio is high, it appears weak and insipid, accompanied by the sharp acidity caused by underextraction.

Extraction Time This refers to the entire extraction time, from locking in the portafilter and pressing the extraction button to the end of extraction. There are two main factors affecting extraction time: grind size and ratio. The ratio is relatively easy to understand: the higher the ratio, the more water is needed for extraction, and the longer the time naturally becomes. Grind size determines the coarseness or fineness of the coffee powder, and the coarseness or fineness directly affects the compactness of the coffee puck—the finer the coffee powder, the denser the puck after tamping, making it difficult for water to penetrate, prolonging the time, and easily leading to overextraction. Generally speaking, the time to extract one espresso is about 20 to 30 seconds.

Flow Rate Flow rate refers to how fast or slow the coffee liquid flows down. The ideal flow rate result is what we ultimately pursue when adjusting various parameters. Normal espresso should begin to drip its first drop of coffee liquid about the fifth second after pressing the extraction button, after which the flow rate remains relatively even. The flow rate can directly reflect whether the grind size and ratio are appropriate. If it takes more than 10 seconds for the first drop to appear (except during pre-infusion), it indicates that the grind may be too fine, or the tamping may be too dense; if the flow rate is too fast or even shows spurting, it indicates that the grind may be too coarse, or channeling has occurred.

Extraction Pressure Usually the extraction pressure of a semi-automatic coffee machine is around 9 bar, which is determined by the machine's performance. Some coffee machines today already have pressure-profiling extraction functions. When the pressure is low, extraction efficiency decreases; when the pressure is high, extraction efficiency increases.

Extraction Temperature The water temperature for extracting espresso is generally controlled between 90 and 94 degrees Celsius. If the water temperature is too high, overextraction is likely, and the coffee tastes bitter; if the water temperature is too low, underextraction is likely, resulting in sharp acidity in the coffee.

So, what other details are worth paying attention to when making espresso?

The process of making espresso can be roughly divided into several steps: weighing the dose, distributing the grounds, tamping, machine extraction, and cleaning. Front Street has also emphasized before that distributing and tamping are crucial to a cup of espresso, and although the impact of the other steps is slightly less, it still cannot be ignored.

There are two points to note when weighing the dose: first, the influence of retained grounds; second, the accuracy of the dose. Carefully observe your espresso grinder. Whether it is a hopper type or a direct-output type, there is a channel between the burrs and the discharge port, where previously ground coffee powder accumulates. If too much time has passed since the last grinding, the flavor of the coffee powder in the channel is already almost gone. At this time, you should use a tool to clean out the retained powder in the channel, or start the grinder and let new powder push out the old powder and discard it, then collect the powder.

Taking the Faema 900N grinder used by Front Street Coffee (FrontStreet Coffee) as an example, the retained coffee powder in its channel can reach 2 grams. If calculated based on 20 grams of powder for a double espresso, this already accounts for one-tenth of the dose, and the impact is evident.

The other issue is the accuracy of weighing. Still taking the Faema 900N as an example, the version used by Front Street is a non-quantitative model, which needs to be assisted by a highly sensitive electronic scale. In order to produce accurately and consistently, the dose should be weighed again for each extraction. Front Street recommends controlling the maximum error within plus or minus 0.1 grams.

If you are using a quantitative grinder, this issue also cannot be ignored. At present, most quantitative grinders use timing as their principle (though there are exceptions, of course), and the problems brought by timing include inconsistent rotation speed, different hopper pressure, inconsistent coffee bean size and density, and so on, all of which can cause errors in the grinding amount.

Inconsistent rotation speed: Inconsistent rotation speed is related to voltage. The domestic voltage is 220V, with a fluctuation of plus or minus 10V. When the voltage is high, the rotation speed is fast; when the voltage is low, the rotation speed is slow.

Different hopper pressure: Each time you grind, the amount of coffee beans stored is different, which leads to inconsistent hopper pressure. Unstable hopper pressure also affects differences in the output dose.

Inconsistent coffee bean size and density: In a blend, different varieties differ in size and hardness, and the proportion of each variety differs with each grinding, which can also cause differences in dose.

During extraction, you should stay organized. From grinding the beans to collecting the powder, distributing, tamping, then locking in the portafilter and pressing the extraction button, in theory this whole set of actions should be completed continuously and should not be intermittent. Therefore, before grinding, first think clearly about what you are going to do next and what is not ready yet. If your operation is not yet proficient enough, you can practice multiple times, and practice makes perfect.

Develop a good habit of cleaning. First, a clean environment makes people feel comfortable; second, cleaning key parts directly affects the quality of the next cup of coffee, such as the retained powder in the grinder hopper mentioned above, as well as retained powder on the distribution tool and tamper. At the same time, make sure that the distribution tool, tamper, filter basket, and other utensils that come into direct contact with coffee powder remain dry (in plain terms, do not let water remain on these utensils), and rinse and clean them after each use.

After extracting an espresso, remember to clean the portafilter and group head as you go, no matter how busy you are. These seemingly insignificant coffee grounds will affect the quality of the next espresso.

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