How to Interpret the Shape of Coffee Grounds in Pour-Over Brewing? Does the Thickness of the Coffee Grounds Wall Affect Coffee Flavor?

Most coffee enthusiasts have developed the habit of observing the coffee bed after brewing. They check if they made any "mistakes" during the pouring process and examine the coffee's flavor to identify potential brewing errors.

Some coffee lovers notice that their brewed coffee always tastes rather "heavy." The coffee bed walls appear relatively thick, with most grounds gathering at the bottom. This leads them to wonder whether the thickness of the pour-over coffee bed might also affect the coffee's flavor.

What factors influence the thickness of the coffee bed?

If you're new to pour-over brewing, you might struggle with determining the appropriate water flow rate. The flow rate not only affects the final extraction time but also changes the distribution of coffee grounds in the filter. A smaller flow rate means weaker agitation of the coffee slurry, less elevation of the coffee bed, and consequently thicker bed walls, forming a slightly curved "bowl shape." Conversely, when using a large flow rate with circular pouring, the coffee bed is lifted higher by the water that hasn't yet filtered through, resulting in thinner bed walls.

Additionally, the size of your pouring circles is another factor that determines bed wall thickness. FrontStreet Coffee typically pours as close to the filter edge as possible without breaking through the coffee bed, resulting in a deeper crater with thinner bed walls. Some coffee enthusiasts prefer pouring in small circles, about the size of a coin, which can cause coffee grounds to concentrate at the bottom, forming thicker bed walls.

Furthermore, thick coffee bed walls commonly occur when brewing dark roast beans. The darker the roast, the more porous the internal structure of the coffee beans. After grinding, these grounds absorb water and expand more easily. Combined with active gas release from the particles, they attach to the filter edges, forming a thick, deep crater.

Does coffee bed thickness affect flavor?

From the perspective of flow rate, smaller flow rates result in longer pouring times and slower drainage, extending the extraction time. This makes over-extraction more likely, leading to undesirable flavors and astringency. Therefore, it's essential to control the extraction process based on timing.

From the perspective of pouring circle size, central pouring or small-circle pouring results in slightly higher actual water temperature compared to large-circle pouring (with approximately 0.5°C difference). This means that larger pouring circles cause more heat loss in the hot water, resulting in slightly lower actual extraction temperatures.

FrontStreet Coffee conducted brewing experiments using the same coffee beans with a V60 dripper. The spiral ribs of the V60 allow coffee to flow along designated paths, preventing clogging. This creates a rich layering of flavors between the coffee extracting within the filter paper and the coffee flowing down along the ribs. FrontStreet Coffee found that coffee brewed with large-circle pouring exhibited more active, light, gentle, and pleasant flavors, while small-circle pouring produced flavors that tended to be fuller, rounder, richer, and more concentrated.

So, is a thicker or thinner coffee bed better?

Since we understand that coffee bed thickness is influenced by these factors, rather than debating the merits of thick versus thin beds, FrontStreet Coffee believes it's better to focus on improving control over brewing water flow. You can adopt more stable techniques tailored to different coffee beans to enhance their flavor and mouthfeel.

For example, when FrontStreet Coffee brews light to medium roast beans (such as Yirgacheffe or Geisha), to highlight the elevated, active fruit acidity, they use a specific technique: after the bloom, the first pouring stage involves moving from the center outward in circles, ensuring all coffee grounds on the surface are thoroughly rinsed until the foam shows consistent color. The final stage involves pouring in concentric circles covering about two-thirds of the liquid surface.

When brewing medium to dark roast beans (such as Blue Mountain or Mandheling), the goal is typically to present a rich, full-bodied flavor. For this, FrontStreet Coffee chooses a KONO dripper with slower drainage and employs small-circle extraction. After the bloom, they again start from the center and slowly move outward in circles, reaching only about half the radius of the possible circle before finishing the pour. Because dark roast coffee releases more gas, even with small-circle pouring, the coffee foam will still surge forth and cover the liquid surface.

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