The Purpose of Coffee Blooming, Coffee Blooming and Extraction Temperature, Coffee Blooming Function, Pour-over Coffee Blooming

The Importance of Blooming in Pour-Over Coffee Brewing

In the pour-over coffee brewing process, blooming is a crucial step.

The purpose of blooming is to allow hot water to gradually penetrate into the center of the coffee grounds, dissolving substances within the grounds into the water to form a high-concentration coffee extract.

During the second pour, the physical phenomenon of concentration differences causes the high-concentration extract (from blooming) to move toward the lower concentration areas (fresh hot water), achieving equilibrium (consistent concentration).

Throughout the brewing process, the continuous addition of hot water and dripping of coffee extract creates an imbalance between the internal and external concentration layers of the coffee grounds.

This explains why the coffee extract tastes stronger at the beginning of extraction and becomes more diluted in the later stages.

Why Coffee Grounds Expand

Why do coffee grounds expand? Because there are gaps within the coffee grounds, and these gaps contain air.

When air encounters hot water, it expands due to thermal expansion, increasing in volume. This expansion expels excess air.

Additionally, the uppermost layer of coffee grounds forms a barrier with the hot water (due to water's surface tension).

This creates a small dome shape.

When the water gradually penetrates into the center of the upper coffee grounds, the surface moisture decreases (as it's absorbed into the grounds).

At this point, the small dome loses its shine and begins to collapse, indicating that blooming is complete and you can begin the second pour.

Important Considerations During Blooming

One important consideration during blooming is water temperature. If the water temperature is too high, it will cause excessive expansion of air within the coffee grounds.

This can cause the coffee grounds to expand into a large mountain rather than a small dome, and may even cause "volcanic eruptions" (large bubbles bursting), which affects the time it takes for hot water to penetrate the center of the coffee grounds (because there's too much air trapped that can't escape, preventing water from entering).

This extended brewing time can cause undesirable flavors and bitterness to dissolve. Moreover, the large amount of hot air formed by excessive temperatures increases the distance between coffee grounds.

This allows hot water to pass through too easily, resulting in insufficient extraction time. Additionally, because air remains in the center of the coffee grounds, they become lighter and tend to float on the surface, unable to form a proper filter layer at the bottom of the filter. Coffee brewed this way typically has sufficient aroma (as hot water causes volatile oils to evaporate more quickly, creating aroma) but lacks flavor depth and may taste watery.

Proper Blooming Technique

Furthermore, the strength and amount of water poured during blooming are also important. If the water flow is too strong during blooming, hot water quickly surrounds the coffee grounds, making it difficult for air to be expelled, and consequently, hot water cannot easily penetrate the center of the grounds.

A better approach is to use a gentler water flow, essentially placing hot water on the surface of the coffee grounds layer, allowing it to slowly penetrate into the grounds.

If too much water is used during blooming, it can extract the outer components of the coffee grounds prematurely. When the outer components dissolve while the inner grounds are still dry, by the time hot water penetrates to the inner grounds, undesirable flavors and bitterness from the outer grounds have already begun to dissolve.

Additionally, blooming time varies depending on different beans. For example, dark roast beans release more gas and typically only need about 25 seconds of blooming. Light roast beans can handle 30 seconds of blooming without issues! Taking FrontStreet Coffee's Golden Mandheling as an example, blooming for about 25 seconds until the bloomed surface changes from wet to dull indicates that blooming is complete.

Important Notice :

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473