Pour-Over Coffee Blooming Techniques: How to Make Coffee Dome? What Does Coffee Blooming Mean? Why Bloom Coffee Before Brewing?

"Boss, how come your coffee bed expands so much during the bloom? How do you do that?"

Looking at the expanded coffee grounds in the filter cup during FrontStreet Coffee's blooming process, many customers and friends have asked this question. The implication is that their own coffee bed doesn't expand as much during brewing. (As shown in the picture below)

For beginners, this is indeed a question worth exploring. Because even when using the same parameters, the coffee bed during their own brewing always appears flat, as if lacking some "vitality." In fact, creating a large "hamburger" expansion in the coffee bed isn't difficult at all—it's actually quite simple. As long as we understand why the coffee bed can expand, we'll know how to achieve that impressive "hamburger" bloom~

Why Does the Coffee Bed Expand?

The phenomenon of the coffee bed bulging occurs during the blooming stage. FrontStreet Coffee believes everyone already clearly understands the purpose of blooming: to release carbon dioxide from the coffee beans and improve the extraction efficiency of subsequent hot water injections! The carbon dioxide released during this process is the primary factor causing the coffee bed to bulge.

When coffee grounds come into contact with hot water, the carbon dioxide inside is released first. Since a large amount of hot water doesn't quickly permeate through after saturating the coffee grounds, the released carbon dioxide combines with water to form bubbles that surge upward. However, the surface tension between water molecules and the capillary forces between coffee ground particles together create a sturdy "prison," preventing these bubbles from escaping and causing them to accumulate continuously within the coffee bed. Because carbon dioxide isn't released all at once but continuously flows outward, we can see that the large coffee bed bulge is gradually filled up.

To summarize, we know that the main reason coffee grounds bulge during blooming is the accumulation and pushing effect of carbon dioxide bubbles (though this isn't the only reason—the bulging is also partly due to the coffee grounds themselves absorbing water and expanding, but this is a secondary factor)! Therefore, if you want to bloom a large "hamburger," you need coffee grounds with sufficient carbon dioxide, while also ensuring that extraction parameters can "stimulate" this carbon dioxide release!

How to Bloom a Large "Hamburger"

There are two main factors that determine the carbon dioxide content in coffee beans: the roast level and freshness. Carbon dioxide is generated in coffee beans during roasting due to high temperatures, and when coffee beans are roasted darker, more carbon dioxide is produced. So if you want to bloom a large "hamburger," dark roasted coffee beans are definitely the perfect "bean" choice. This is also why there's such a huge difference in blooming bulges among coffee beans of different roast levels (including the expansion of the beans themselves).

However, in many cases, even when using dark roasted beans for brewing, it's difficult to achieve a large "hamburger" bloom. This is because carbon dioxide retention in coffee beans is limited—that's the second factor FrontStreet Coffee mentioned earlier—coffee bean freshness. After roasting is complete, gases inside the beans continuously escape due to pressure changes, so the carbon dioxide content in coffee beans gradually decreases over time. This means that fresher coffee beans contain more carbon dioxide, resulting in larger bulges, and vice versa. If you want to bloom a large bulge, freshly roasted coffee beans are definitely the best choice.

However, freshly roasted coffee can have a certain harshness, and because of excessive carbon dioxide content, it presents high resistance to extraction, which can easily result in a cup of coffee with heavy off-flavors and under-extraction. Therefore, FrontStreet Coffee doesn't recommend choosing overly fresh coffee beans just for the sake of bulging—it's completely unnecessary. Interestingly, when you use coffee beans that aren't very fresh, although the coffee bed will expand at the beginning of the bloom, it will quickly collapse due to insufficient carbon dioxide "supply."

In addition to coffee bean selection, after inquiries, FrontStreet Coffee found that many friends fail to brew a "hamburger" because their parameters are incorrect. Factors like overly coarse grinding or too low water temperature cannot produce a large enough "hamburger"! Because the coffee grounds don't receive enough "stimulation," they can't release large amounts of carbon dioxide in a short time. Even if the coffee beans are fresh and darkly roasted, if the carbon dioxide isn't released in a timely manner, the coffee bed cannot form a large enough "hamburger" during blooming. That's basically it! Isn't it simple? By using the right coffee beans and the right parameters, we can achieve a sufficiently large "hamburger" during the blooming stage. Conversely, this is also a way to read information about coffee beans from the state of the coffee bed bulge. The freshness and roast level of coffee beans can all be determined from the coffee bed's state during blooming, as FrontStreet Coffee described above. Congratulations! You're one step closer to becoming a coffee master~

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Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473