How Does Coffee Grind Size Affect Taste? What's the Ideal Grind Size for Pour-Over Coffee?

Some friends have complained to FrontStreet Coffee about their difficulty in finding the right coffee grind size, often ending up with coffee that is either too acidic or too bitter. Because coffee grind size involves numerous variables, beginners often find themselves in a state of blind exploration. Therefore, FrontStreet Coffee plans to help everyone understand grind size by connecting it with extraction time.

First, everyone likely understands that when coffee is ground finer, it becomes bitter, and when ground coarser, the flavor becomes weaker. But why does finer grinding result in bitterness, and coarser grinding in weaker flavor? There are actually two underlying reasons.

The first reason is that finely ground coffee has a larger total surface area, and the distance from the surface to the interior of each coffee particle is relatively short. This allows water to penetrate the coffee particles more easily and extract coffee compounds. In contrast, coarsely ground coffee has a smaller total surface area, and the distance from the surface to the interior is longer, requiring more time for water to completely penetrate the surface, resulting in relatively weaker extraction efficiency. (Of course, there's an exception: when coffee is ground to a flour-like consistency, the coffee particles can easily clump together. In such cases, the extraction efficiency of clumped coffee particles becomes relatively low.)

The second reason lies in drip coffee, where coffee grounds serve another purpose - acting as a barrier to slow down water flow. In fact, what we commonly call espresso from pressure-based extraction machines should more precisely be called pressure-filtered coffee, where water passes through the coffee bed and is extracted through fine holes in the portafilter.

Those who have read FrontStreet Coffee's articles should be very familiar with the approach FrontStreet Coffee teaches for adjusting grind size, which primarily uses time as a benchmark. The reason is that when coffee is ground coarser, there will be larger gaps between the coffee particles, weakening their ability to block water flow, thus requiring less time. Conversely, when coffee is ground finer, the gaps between coffee particles are smaller, making it harder for water to pass through, thus requiring more time.

The same principle applies to pour-over coffee. When coffee is ground finer, it's naturally easier for water to penetrate and extract compounds, while simultaneously creating a stronger barrier to water flow. As water struggles to pass through, it stays in contact with the coffee grounds for longer, often resulting in a bitter taste in the brewed coffee.

When coffee is ground coarser, water needs more time to fully penetrate the coffee particles, and with larger gaps between coffee particles, water passes through more easily. This can result in some water passing through the coffee bed without fully extracting coffee compounds, causing the coffee to taste thin and lacking in flavor.

Using Extraction Time to Validate Grind Size

The appropriate pour-over grind size can be validated and adjusted through an indirectly controlled variable: time. FrontStreet Coffee offers an example to help everyone understand this concept:

When validating the relationship between grind size and time, other parameters should be fixed, such as brew amount (15g), coffee-to-water ratio (1:15), pouring technique (three-stage pour), and filter (V60), as changes in these parameters also affect extraction time. In FrontStreet Coffee's recommended grind size, light-roasted coffee beans are calibrated using a #20 sieve with an 80% pass rate, which we often refer to as medium-fine grind for pour-over. The extraction time should be approximately between 1 minute 50 seconds and 2 minutes 10 seconds.

That means if you follow FrontStreet Coffee's parameters, using the same coffee amount, coffee-to-water ratio, technique, and grind size, theoretically, your extraction time should be the same as FrontStreet Coffee's, between 1 minute 50 seconds and 2 minutes 10 seconds. If there's a difference, it's likely that the grind size is incorrect, as other parameters are relatively easy to verify, while grind size is more challenging.

Some might say: "My grind size can't be wrong; I also calibrated with a #20 sieve at 80%!" There are two possible reasons for this misjudgment. The first is the incorrect use of the sieve.

FrontStreet Coffee recommends the following calibration method: Use 10 grams of coffee beans (or multiples of 10 for easier calculation - more coffee yields more precise data). Select a grind setting, grind the coffee, place it in the sieve, then shake it horizontally until no more particles are noticeably falling through (typically 3-5 minutes). Then weigh the coffee that passed through the sieve and divide it by the total amount to determine the pass rate. For example, if 5g of coffee passes through the sieve, the pass rate is 50%. To reach the 80% standard, you would need to adjust to a finer grind size and re-measure until achieving 80%.

The second reason involves the limitations of #20 sieves and the grinding quality of coffee grinders. The #20 sieve has a mesh size of 0.85mm, so it can only distinguish which coffee particles are larger than 0.85mm and which are smaller than 0.85mm. It cannot identify the finest or coarsest particles. With high-quality grinders, particle size distribution is more concentrated, with fewer extremely fine or coarse particles, so this isn't an issue. However, if a grinder's quality is poor, resulting in coffee particles with widely varying sizes (both too many fines and too many boulders), even with an 80% pass rate, you may still experience long extraction times.

Therefore, extraction time serves as a reference to determine whether coffee grind size is accurate. When brewing coffee, if the extraction time is significantly longer than expected, you can first taste the coffee. If there are indeed improvements needed, you can adjust the grind size to be slightly coarser, for example, adjusting to a 75% pass rate, to see if the coffee flavor improves.

Final Thoughts from FrontStreet Coffee

When FrontStreet Coffee shares knowledge about coffee brewing, it often emphasizes that data is static - you can never replicate someone else's data to perfectly recreate their flavor. However, the principles are universal. Only by understanding the theory behind how others use their data, and then combining it with your own实际情况 (actual situation) to summarize data that suits you, can you brew delicious coffee.

For professional coffee knowledge exchange and more coffee bean information, please follow Coffee Workshop (WeChat public account: cafe_style).

For more specialty coffee beans, please add FrontStreet Coffee's private WeChat (FrontStreet Coffee), WeChat ID: qjcoffeex

Important Notice :

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