Pour-Over Coffee Grind Size Reference & Adjustment Methods for Coffee Grinder Settings

Understanding Coffee Grinding: Techniques and Burr Types

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Regardless of the coffee extraction method, grinding is always a necessary step. Different extraction methods require different grind sizes, with the most obvious difference being between coffee grounds used for espresso machines versus those used for pour-over methods. So how do we determine what grind size is needed for different coffee preparation methods?

FrontStreet Coffee's Grind Size Theory

No grinder can achieve absolutely uniform grinding; in a single grinding session, there will always be coarse particles, fine particles, and even extremely fine particles. This is difficult to distinguish with the naked eye. Therefore, FrontStreet Coffee uses sieves to assist in determining the grind size.

For pour-over methods, FrontStreet Coffee uses the National Standard No. 20 sieve for calibration. The No. 20 sieve has a pore diameter of 0.85mm, meaning coffee particles larger than 0.85mm cannot pass through.

FrontStreet Coffee's Grind Size Standard Sieve Pass Rates:

Cold Drip > Pour-over, Syphon 80% > American Drip 75-80% > Cupping 70-75% > French Press 65-70%

This method provides a more intuitive representation of the required grind size values. FrontStreet Coffee uses a grind size with an 80% pass rate through the No. 20 sieve for brewing light-roasted coffee, while a 65%-70% pass rate is used for medium-dark roasted coffee.

How to Adjust a Grinder?

First, let's understand the types of burrs in coffee grinders, which can be categorized as flat burrs, conical burrs, and ghost teeth.

Flat Burrs

Flat burr grinders consist of upper and lower burrs, with the base fixed to the motor. When the motor starts, the rotation of the upper and lower burrs creates a cutting action.

When coffee beans fall from the center, the rotating lower burr pushes the beans to the periphery, advancing them into the teeth section for grinding.

Since the upper and lower burrs of flat burrs are arranged parallel, coffee beans need to rely on the force from the rotating lower burr to advance into the burrs. Therefore, the weight of the coffee beans placed on top will affect the uniformity of beans entering the burrs, which in turn affects grinding uniformity. Additionally, the pushing motion increases collisions between coffee beans, leading to a higher proportion of fine particles. This is why flat burr grinders typically have slightly less uniform particle size and more fine particles.

Coffee particles ground by flat burrs appear flaky, and this shape increases the surface area of the cell walls. Therefore, using flat burrs can increase coffee concentration and extraction rate in a short time, significantly enhancing coffee aroma quickly. At the same time, because of their flat, elongated shape and smaller volume, when extraction time is prolonged, the woody parts of the particles will absorb excessive water, leading to increased bitterness and astringency.

Conical Burrs

Conical burr grinders have a cone-shaped burr at the bottom, working with an outer ring burr for grinding. After coffee beans fall from above, they are pulled downward by the rotation of the cone-shaped burr, creating the grinding action. Because of this top-to-bottom movement, particles don't need to be pushed out, reducing the number of collisions between particles compared to flat burrs. Therefore, conical burrs produce fewer fine particles than flat burrs, and coffee grinding uniformity is significantly improved.

Particles ground by conical burrs are more granular, resulting in longer water absorption paths. The interior takes longer to contact water, so conical burr particles release fewer soluble substances in the initial stages, leading to lower concentration in a short time. At the same time, because of their granular shape, even with longer extraction times, the woody parts absorb less water, making them less likely to produce bitterness and astringency.

Ghost Tooth Burrs

Ghost tooth burrs grind coffee beans into particles primarily through a grinding motion, resulting in shapes that closely resemble spheres. However, because they can grind a single coffee bean into several small spherical particles, the edge waste (fine particles) produced from grinding these spheres also increases. But the overall difference between large particles is minimal. Suitable for pour-over grinding.

For new grinders or those that have been disassembled for cleaning and reassembly, the relationship between grind size and scale settings is not fixed. For example, FrontStreet Coffee's daily use grinder, Forte-BG, had a 6S scale setting corresponding to an 80% pass rate through the No. 20 standard sieve before cleaning. After cleaning and reassembly, the 6S scale setting corresponded to a 75% pass rate. Therefore, whether new or old, grinders need to be calibrated periodically.

Adjusting New Grinders

FrontStreet Coffee uses a certain brand of grinder for demonstration. This grinder has 10 settings, meaning there are 10 grind settings to choose from. First, select a finer setting and a coarser setting to determine the range.

First, setting 2 was selected for grinding adjustment:

10 grams of grounds all passed through, with a 100% pass rate. It feels as fine as flour to the touch, similar to espresso grounds. Some might ask, why not use setting 1? Because when adjusted to setting 1, obvious burr collision sounds could be heard, indicating it was already completely tightened, so the editor chose setting 2 for testing.

Next was setting 10: 10 grams of grounds with 2.8 grams passing through, a 28% pass rate.

Therefore, this grinder has a wide range of values. The wider the range and the fewer settings between, the fewer grind size options available (lower precision).

Next, we selected the middle setting 5 for adjustment: 10 grams of grounds with 6.8 grams passing through, a 68% pass rate.

This is quite close to the 80% grind size we use, so setting 4 was used for adjustment: 10 grams of grounds with 7.8 grams passing through, a 78% pass rate. Because the grinding difference between each setting is quite large, setting 4 is the closest to our required grind size, so setting 4 can be considered the grind size for pour-over products.

Generally, when adjusting grinder grind size, we first look at the sieve pass rates for the finest and coarsest grinds, then take a middle value for fine-tuning. If you don't have sieves at home, the only way is through the most intuitive method—tasting the flavor of the brewed coffee to make adjustments!

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Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473