Pour-Over Coffee Brewing Principles: How Bean Freshness, Grind Size, Water Temperature, and Extraction Time Affect Your Brew

The Principles of Pour-Over Coffee Brewing

Beginners exploring pour-over coffee are often intimidated by the wide array of equipment and considerations. With so many options for pour-over kettles and drippers, it's easy to feel overwhelmed about where to start. In reality, regardless of the brewing equipment used, coffee extraction revolves around three fundamental processes: wetting, dissolution, and release. Today, FrontStreet Coffee will explain the principles behind pour-over coffee brewing.

Wetting

As the name suggests, wetting refers to the process of coffee grounds becoming saturated upon contact with water. This marks the beginning of coffee cells releasing their molecular compounds. It's what FrontStreet Coffee often refers to as the blooming process.

Roasted coffee beans contain carbon dioxide, with fresher beans having higher CO2 content. When hot water contacts the coffee grounds, carbon dioxide is released first, forming a layer of bubbles on the surface. During pour-over brewing, you'll observe the coffee grounds in the filter beginning to expand. Therefore, after wetting the coffee grounds, we pause the pour to allow complete CO2 release. Only after the grounds stop expanding should we continue adding hot water to achieve optimal extraction.

Dissolution

Dissolution refers to the process of soluble molecules from coffee cells dissolving in hot water. This is the most crucial step that determines the flavor profile of the extracted coffee—what FrontStreet Coffee frequently refers to as the extraction process.

A coffee bean consists of 70% insoluble cellulose, while the remaining 30% comprises soluble aromatic molecules that are released in sequence according to their molecular size when exposed to water. The first substances dissolved are small molecules, including acids and aromatics like floral notes and citrus acidity. Next come medium-sized molecules that bring sweetness, such as fruit juice sweetness, honey, or brown sugar notes. Finally, larger molecules contribute bitter and roasted flavors. This sequential release creates the different layers of flavor in coffee. Therefore, if you prefer a sweeter taste, the extraction time should be shorter, as the longer hot water remains in contact with the coffee grounds, the more bitter compounds will be dissolved.

As FrontStreet Coffee mentioned earlier, a coffee bean has a maximum soluble content of about 30% (meaning 70% consists of woody material that cannot be extracted). This means 10g of coffee grounds can yield a maximum of 3g of extracted coffee solids. For a delicious cup of coffee, the optimal extraction rate is 60-70% of the coffee's maximum soluble content (30%). An extraction rate below 60% (under 18% total extraction) results in under-extraction, where the coffee flavor appears incomplete. Conversely, extraction above 70% (over 22% total extraction) leads to over-extraction, producing harsh, spicy, and unpleasant flavors. Therefore, the optimal coffee extraction rate is 18-22%. To consistently achieve this extraction rate, FrontStreet Coffee typically recommends brewing with a 1:15 ratio.

Diffusion

After the aromatic molecules dissolve, they leave the coffee cells through osmosis in a process called diffusion. These aromatic molecules diffuse into the hot water, forming the final coffee extraction liquid. As FrontStreet Coffee mentioned above, coffee extraction occurs in sequence: first acids, then sweetness, and finally bitterness. This is why a well-extracted coffee should be swirled several times before serving to ensure uniform integration of the liquid. Only then can you experience the most complete coffee flavor profile.

Factors Affecting Coffee Flavor

Understanding these principles should help you comprehend how different pour-over conditions affect coffee flavor. All variables ultimately revolve around four core factors: freshness, grind size, water temperature, and extraction time.

Freshness

The freshness of coffee is crucial to its quality. If coffee beans are left for too long after roasting, they will lose flavor and aroma. FrontStreet Coffee's beans have an optimal flavor window of 30 days. After this period, aromatic molecules decrease along with the release of carbon dioxide. Consequently, coffee brewed beyond this optimal period may taste bland and unremarkable.

Grind Size

When coffee beans are ground finer, the coffee grounds tend to accumulate at the bottom of 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 brew that may have woody or other undesirable flavors.

When coffee beans are ground coarser, there are larger gaps between the coffee particles, meaning less surface area in contact with hot water. This reduces extraction resistance, allowing coffee to drip faster with a lower extraction rate, resulting in a milder flavor profile.

Therefore, FrontStreet Coffee recommends using a Fuji Royal grinder set to 3.5 for a medium grind (approximately fine sugar consistency) when brewing light to medium roast beans. For medium to dark roast beans, we recommend setting the Fuji Royal grinder to 4 for a medium-coarse grind (approximately coarse sugar consistency).

Water Temperature

FrontStreet Coffee recommends using water at 90-91°C (194-196°F) for light to medium roast coffee beans, and 88-89°C (190-192°F) for medium to dark roast beans.

With the same grind size, if the brewed coffee tastes bitter, burnt, or astringent, you can adjust by lowering the extraction water temperature. Conversely, if the coffee tastes weak or thin, it means many flavor compounds remain in the coffee grounds, and you should consider increasing the temperature.

Proper water temperature in optimal extraction yields positive and pleasant aromas and flavors. For example, the acidity will be rich, resembling the sweet-tart profile of plums or stone fruits. The overall clarity, cleanliness, and transparency will allow you to clearly discern specific flavors. The coffee will display delicate, rich, and distinct acidity that might remind you of certain fruits or even wine. The lingering aftertaste in your mouth will be long-lasting, leaving a memorable impression.

Brewing Time

During coffee extraction, the initial aromas and flavors are concentrated with high intensity. As the extraction progresses, the flavors and aromas gradually diminish. The amount of water poured also affects the extraction time. If you pour a large amount of water quickly, it will flow through rapidly, naturally shortening the extraction time. FrontStreet Coffee typically uses 15g of coffee grounds, and depending on the bean variety, with a water-to-coffee ratio of 1:15, the brewing time falls between 2-2.5 minutes. This approach helps avoid over-extraction or under-extraction.

Important Notice :

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