How to Determine Coffee Grind Size? Can Coffee Grounds Be Brewed Directly?

When FrontStreet Coffee explains pour-over coffee, we always mention several important factors that affect coffee extraction or flavor, including water temperature, grind size, and coffee-to-water ratio. Among these, the grind degree determines the size and uniformity of coffee particles, directly affecting the efficiency of water flow extracting flavor compounds from the coffee grounds. So in daily brewing, how should we determine the appropriate grind size for different coffee beans? In this article, FrontStreet Coffee will explain how to adjust the grind coarseness for pour-over coffee.

The Impact of Grind Coarseness on Coffee Extraction

Through various brewing experiments, FrontStreet Coffee has demonstrated that the finer the grind, the more easily the coffee grounds accumulate on the filter paper, creating greater extraction resistance. This results in slower flow rate and longer extraction time. The extraction rate of coffee compounds is higher, producing a more intense brewed coffee. Similarly, the coarser the grind, the larger the gaps between particles, meaning less coffee comes into contact with hot water, resulting in weaker extraction resistance. Coffee drips through faster, the extraction rate is lower, and the coffee flavor is milder. So what are the characteristics during the brewing process when coffee beans are ground too fine versus too coarse?

What Happens When Pour-Over Coffee Beans Are Ground Too Fine?

From the appearance of the coffee particles, the particle size is smaller. Because the particles are smaller, the spacing between particles is shorter, making it more difficult for water to pass through them, resulting in longer drip times during brewing. The finer grind creates smaller particles, and when the coffee grounds get wet and filter, they present a paste-like consistency. After brewing, it's difficult to see individual coffee particles in the coffee bed, with most showing an obviously pasty state.

What Happens When Pour-Over Coffee Beans Are Ground Too Coarse?

From the appearance of the particles, the particle size is larger. Because the particles are larger, the spacing between particles is greater, making it easier for water to pass through the coffee grounds, resulting in shorter filtration times during brewing. The coarser grind creates larger particles, and after brewing, individual coffee particles are clearly visible in the coffee bed. It's difficult to form a complete coffee bed, and there are gaps or fractures.

The Impact of Grind Size on Coffee Extraction

The grind degree means not only the size and shape of coffee after grinding but also the surface area. The finer the coffee is ground, the larger the surface area, and the increased contact area between water and coffee allows for extracting more compounds. The increased surface area also provides more places for carbon dioxide inside the coffee beans to be released.

How We Adjust Pour-Over Coffee Grind Size

When grinding coffee daily, the difference between the largest and smallest particle values in seemingly uniform coffee grounds is at least 0.6mm. Generally, we call coffee particles larger than 0.85mm "coarse grounds," while particles smaller than 0.25mm are called "very fine grounds." If these two types of grounds account for more than 40% of your total grounds, they are not suitable for pour-over coffee. Don't understand? No problem! FrontStreet Coffee recommends everyone purchase a 0.85mm aperture test sieve.

How to Use a Sieve to Determine Coffee Grind Size?

Weigh 10g of coffee beans, adjust to an approximate grind size and grind into coffee powder, then pour into the sieve for screening. Weigh the screened coffee grounds (make sure to sieve until no more coffee powder can pass through). A pass rate of 75%-80% (10g of grounds yielding 7.5-8g through the sieve) is the most suitable grind size for light to medium roast coffee beans. A pass rate of 65%-70% (10g of grounds yielding 6.5-7.0g through the sieve) is the most suitable grind size for medium to dark roast. If you exceed the appropriate pass rate, adjust the grind to be coarser. If you don't reach the appropriate pass rate, adjust the grind to be finer.

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