Why does hand-drip coffee bloom like a hamburger that rises and then collapses? Is this normal?

Blooming, a preliminary action that involves moistening the coffee grounds with a small amount of water and waiting for several tens of seconds. When the coffee grounds form a fluffy and uniform "dome" as expected, we can generally determine that the coffee beans are still fresh and in a good tasting state. If the grounds show no intention of rising at all, or even sink directly, the coffee beans have likely been stored for too long and are no longer fresh, and we might suspect that the brewed coffee will taste mediocre.

The Third Scenario: Blooming Collapse

In addition to the two outcomes mentioned above, some careful friends have informed FrontStreet Coffee that they've discovered a third scenario: after completing the water pour, although the coffee grounds briefly bubble up, they immediately begin to collapse, and the coffee bed sinks down in an instant. Is this considered a normal phenomenon?

Why Do Coffee Grounds Collapse Immediately After Expanding?

The reason blooming can form a dome is mainly due to the interconnection effect between particles as they become moistened. With the simultaneous release of gases, the entire coffee bed is pushed upward, thereby forming a loose and stable degassing structure.

Once the stable structure between the coffee particles is disrupted by "external forces," and large gaps that cannot bond together appear in certain parts of the dome, the gases lose the support of the coffee grounds and naturally collapse downward. Since the particles showed expansion after absorbing water, it indicates that these coffee grounds were once in a "degassing" state, so we can first rule out the possibility that the coffee beans are not fresh. Coffee beans with almost completely released gases will show little to no signs of rising during blooming, and their flavor will be greatly diminished.

So, what causes this "expansion followed by immediate collapse" situation? Based on FrontStreet Coffee's brewing experience, this is mainly caused by the following reasons.

Excessive Water Amount

Under normal circumstances, the saturation water absorption of coffee grounds is about twice their own weight. Therefore, whether it's the brewing tutorials we refer to daily or the extraction insights from some baristas, the blooming water amount is always twice the amount of coffee grounds, meaning 15 grams of coffee grounds corresponds to 30 grams of water. However, for newcomers who are still unfamiliar with flow control techniques, sometimes it's inevitable to accidentally pour too much water. If brewing light-roasted coffee beans with weaker water absorption, not only will more blooming liquid drip into the lower pot, but there may also be situations where the dome is "pressed" down by gravity.

Using FrontStreet Coffee's common 15-gram amount for brewing Yirgacheffe coffee as an example: a small stream of water poured in a circular pattern from the center with 30 grams of water not only moistens all the particles appropriately, but the formed dome remains stable even at 30 seconds. When using 45 grams or more of hot water for blooming, we can observe that the water level of the coffee grounds will rise, and more coffee flows into the lower pot. After all the blooming liquid has dripped into the lower pot, the previously risen hamburger-shaped dome also shows slight contraction.

Coffee Grounds Are Too Coarse

Friends familiar with pour-over parameters should know that a delicious cup of coffee cannot be achieved without uniform and moderate grinding fineness. For pour-over beginners, FrontStreet Coffee usually recommends first visually estimating sugar-sized coarseness, then determining whether fine-tuning is needed by considering whether the extraction time falls within a reasonable range (around 2 minutes), and whether to make it coarser or finer. If conditions permit, it's best to equip a #20 standard sieve with a 0.85mm diameter for screening, controlling the grinding fineness to achieve a screening rate of 70-80%.

When coffee grounds are ground too coarsely, the most obvious consequence is that water flows into the lower pot before it has time to penetrate the interior of the coffee particles, leading to under-extraction. During the blooming stage, larger coffee particles will release gases upon initial contact with water, causing the coffee bed to expand first. As hot water flows through the gaps between the large particles into the lower pot, these cracks don't have time to "bond" back together, and the dome quickly begins to contract, resulting in collapse.

Too Strong Water Pouring Force

A gentle small stream of water poured in a circular pattern from the center outward is the blooming technique most people use. This creates a dome that slowly expands from the middle to the surroundings until it fills the entire bottom of the filter cup.

However, if using a more aggressive pouring technique and focusing only on pouring in a small circle at the center, the water stream directly impacts the coffee grounds, causing the distance between particles to increase. The center can rise mainly because gases are being released, obstructing the water's descent. When all the gases have been released, the water begins to flow downward, leaving behind a hollow coffee bed that naturally tends to collapse.

Conclusion

In summary, when the coffee grounds rise and then collapse during blooming, this is clearly not a normal phenomenon. Although it cannot directly indicate that the coffee tastes wrong, it does reflect that there are problems with our parameters or techniques. We need to find the root cause by combining it with the final taste, then "prescribe the right remedy" to solve it from the details.

FrontStreet Coffee

10 Bao'an Qianjie, Yandun Road, Dongshankou, Yuexiu District, Guangzhou, Guangdong Province

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473