Why doesn't the coffee bed form a "hamburger" shape during pour-over blooming? Detailed guide to blooming water pouring techniques

When brewing freshly roasted coffee, observing the coffee grounds expand and form a round dome as they release gas when encountering hot water is one of the great pleasures for many pour-over enthusiasts. But when the coffee bed doesn't rise during the blooming stage, or even "sinks" downward, we might wonder if something went wrong and whether this cup of coffee will taste good.

Why Does Coffee Form a "Dome" During Blooming?

During the roasting process, the roaster provides a large amount of thermal energy to the coffee beans, causing the internal structure of the beans to continuously expand. This further opens the pores in the cell walls of the raw beans, storing a large amount of carbon dioxide. As roasting completes and the coffee beans return to room temperature, these carbon dioxide gases begin to gradually release.

The most important purpose of blooming is to help the coffee grounds release most of the carbon dioxide appropriately while "awakening" the soluble substances in the coffee, allowing for better extraction of various aromatic flavors in subsequent brewing. The "dome" we see is the process of gas release from within the coffee grounds - the higher and longer the dome persists, the more intense the gas release.

What Causes the Lack of Dome Formation During Blooming?

1. Coffee beans are not fresh

From an extraction perspective, the carbon dioxide content in coffee beans has both advantages and disadvantages. During daily storage, the abundant gases contained within unground beans can hinder the volatilization of flavor compounds. However, during brewing, these gases that "scatter randomly" when encountering water can obstruct our ability to extract various aromatic components. This is where blooming becomes a crucial extraction aid.

Under normal circumstances, properly stored coffee beans will have released most of their carbon dioxide within forty to fifty days after roasting. When the gases are gone, no "dome" will form during blooming, and the aromatic substances will have lost their resistance, dissipating along with the gases. The resulting brewed coffee will be significantly diminished in quality.

2. Grind is too coarse

When the grind is too coarse, the gaps between particles will increase. Under the influence of gravity, the poured hot water will flow into the lower pot before it can fully penetrate the interior of the coffee grounds. The particles cannot receive support from water, and gas will escape along the broken gaps, causing the entire coffee bed to collapse.

This situation typically occurs when switching to new beans. For example, if the previous grind setting was suitable for medium-dark roast coffee, and later you switch to anaerobic fermented beans (which are much fluffier than traditionally processed beans of similar roast degree), the overly coarse grind will prevent dome formation during blooming. If the coffee you brew also lacks a dome, tastes "watery," and has an extraction time of less than 1 minute and 55 seconds, FrontStreet Coffee suggests slightly adjusting the grind to be finer (like raw sugar) to balance the extraction rate.

3. Not all coffee grounds are fully saturated

Some friends pay too much attention to the amount and timing of water during blooming, but their water control skills need improvement. After pouring the initial blooming water amount, some particles remain dry. This causes the raised coffee bed to lean to one side, making it difficult to form a "stable dome." The blooming becomes incomplete, and the resulting coffee is likely to have uneven extraction. If you truly cannot fully saturate all coffee grounds within 2 times the coffee weight, then add a little more water (about 5 grams) to ensure all coffee grounds are soaked and release gas.

4. Too much water poured or too much force applied

When developing brewing recipes, we typically adopt a blooming formula of "2 times the coffee weight in water for 30 seconds," which is also a relatively safe method for brewing unfamiliar beans. However, when we pick up the pour-over kettle, our control over water flow sometimes deviates from the plan. The most common situation is accidentally pouring too much water. Since coffee grounds can only absorb about twice their weight in blooming liquid, excess water will flow along the filter cup edges into the lower pot due to gravity, causing the dome to collapse.

FrontStreet Coffee has experimentally compared this - as long as the water amount is well-controlled during blooming and the coffee bed is evenly saturated, the direction of circular pouring and water flow size don't have a significant impact on extraction results. However, if the pouring force is too strong and the water column directly impacts local coffee bed particles, gas release will be uneven - more on one side and less on the other. The coffee bed cannot form a stable supporting surface and naturally collapses.

Therefore, to achieve an ideal blooming dome, FrontStreet Coffee suggests using a small amount of water (for 15 grams of coffee, control blooming water within 35 grams) and pouring evenly and gently in circular motions from the center outward. This allows the coffee grounds to be evenly saturated, forming a rounded "dome" shape.

5. Roast is too light, resulting in不明显 dome formation

Very lightly roasted coffee beans, due to their shorter time out of the roaster, have hard bean texture and lower gas content. Therefore, during the blooming stage, they won't show significant expansion, performing similarly to stale coffee beans. The golden foam that appears during subsequent water pouring will be thin. However, this doesn't affect their flavor. Some light roast coffee beans show similar phenomena - during blooming, the coffee dome is not obvious, with only slight swelling, which is also a normal phenomenon.

Important Notice :

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