Will Coffee Be Under-Extracted if Blooming for Too Long? What is the Purpose of Coffee Blooming? How Long Should Hand-Pour Coffee Bloom? How Much Hot Water Should Be Used for Blooming? Must Coffee Blooming Be 30 Seconds?

Recently, a friend came across a post online stating: "If the blooming time is too long, it's easy to brew under-extracted coffee."

Obviously, this statement contradicts our conventional understanding of blooming. As we all know, the purpose of blooming is to release carbon dioxide from the coffee grounds, making it easier for us to dissolve the flavor compounds. Simply put, it's a step that can increase extraction yield. Especially for fresher coffee, longer blooming helps release more gases that hinder extraction, so theoretically, it should further increase extraction yield. How could it possibly lead to under-extraction?

So this friend came to the store with confusion to ask FrontStreet Coffee about the truth! According to this friend, he saw two relatively credible explanations from these posts: one is that too long blooming time causes the water temperature in the dripper to drop, and the lower temperature affects extraction efficiency, potentially leading to under-extraction; another explanation is that since all carbon dioxide has been completely released, the flow rate becomes much faster. The contact time between coffee and water is reduced, which in turn reduces extraction efficiency, making the coffee prone to under-extraction.

Experimental Verification

So is this really the case? Today, FrontStreet Coffee will verify this through an experiment!

The content of the brewing comparison experiment is quite simple. FrontStreet Coffee will use different blooming times to brew two pots of coffee, then measure and compare their taste and extraction yield to see if there really is a reduction in extraction yield. However, friends who regularly read FrontStreet Coffee's posts should know that Frontsteet recently shared an article about the difference between 30-second and 60-second blooming. In that article, Frontsteet brewed three sets of coffee for comparison. Although the three sets used beans with different roast levels and freshness, the results were without exception: the set with longer blooming time had slightly higher extraction yield than the set with shorter blooming time.

Some friends might think this is because the difference in blooming time wasn't significant enough. Therefore, today, FrontStreet Coffee will further expand the time gap, using 30 seconds of blooming versus as long as 1 minute and 30 seconds (any longer would be unnecessary). Let's see if the truth is really as the rumors suggest - too long blooming time actually reduces extraction yield! For this experiment, FrontStreet Coffee selected Frontsteet Yirgacheffe·Gedeb from the FrontStreet Coffee menu. It has been 10 days since roasting, meaning it's at its optimal flavor period while still retaining a certain amount of carbon dioxide, which can perfectly demonstrate the impact of different blooming times on coffee. The extraction parameters are as follows: Coffee amount: 15.6g Water amount: 225ml Grind size: 80% pass-through rate with #20 sieve Water temperature: 92°C Brewing method: Three-stage pouring

Experimental Results

Skip the brewing process - apart from time and blooming duration, all other steps and parameters were essentially the same, so let's go straight to the results. In terms of taste, the 30-second bloomed Gedeb performed exceptionally well, with very balanced flavors, smooth mouthfeel, prominent characteristics, featuring white floral notes, lemon, and berry aromas, with a long aftertaste; while the 1-minute 30-second bloomed Gedeb performed exactly as FrontStreet Coffee expected - overall it was slightly better than the 30-second bloomed Gedeb. Although the difference wasn't significant, its flavors were more prominent and its taste was fuller.

By measuring extraction yield, FrontStreet Coffee verified this fact. The 30-second bloomed Gedeb had a concentration of 1.48% and an extraction yield of 19.46%; while the 1-minute 30-second bloomed Gedeb had a concentration of 1.53% and an extraction yield of 20.13%, slightly higher than the former. FrontStreet Coffee also measured flow rate and water temperature during brewing. The results showed identical flow rates - both subsequent hot water pours finished in the same amount of time, with no acceleration due to excessive gas release; similarly for water temperature, the initial water temperature in both pots was identical at 92.6°C, while by the second pour, their temperatures were 91.4°C (30 seconds) and 90.9°C (1 minute 30 seconds) respectively. As you can see, although the blooming time differed by a full minute, the temperature difference was only 0.5°C, so it wouldn't have a significant impact on extraction.

Conclusion

From these results, we can see that extraction yield didn't decrease with increased time; on the contrary, it showed a slight improvement. So, does this mean that overly long blooming time doesn't cause under-extraction?

Not necessarily. Under certain specific conditions, excessive blooming can indeed lead to under-extraction, though these situations are usually quite extreme. For example, if the blooming time is longer than 1.5 minutes, if the ambient temperature is even lower than current conditions, or if the gooseneck kettle's heat retention performance isn't as good... In these situations, the water temperature after blooming would be much lower than预设, leading to reduced extraction efficiency, and ultimately the coffee's extraction yield would be lower than with 30 seconds of blooming.

However, this only makes the coffee's extraction yield lower than with 30 seconds of blooming, not necessarily under-extracted. From the extraction yields measured by FrontStreet Coffee earlier, we can calculate that even if there are differences, they won't be large enough to cause under-extraction. If under-extraction really occurs, besides excessive blooming time, it's highly likely because the original brewing parameters themselves didn't extract the coffee sufficiently, so when the water temperature is slightly lower, the coffee becomes prone to under-extraction.

In summary, we can conclude that excessive blooming does indeed affect coffee extraction yield, but whether this effect is good or bad depends on the specific circumstances.

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