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 claiming that "if the blooming time is too long, it is easy to brew under-extracted coffee."

That statement clearly contradicts our usual understanding of blooming. As everyone knows, the purpose of blooming is to release carbon dioxide from the grounds so that flavor compounds dissolve more easily. Put simply, it is a step that raises extraction yield. Especially with fresher coffee, a longer bloom helps release more of the gas that gets in the way of extraction, so in theory it should raise extraction yield further. How could it possibly cause under-extraction?

So the friend came to the store to ask FrontStreet Coffee for the truth. According to him, the post offered two fairly credible explanations. One is that too long a bloom drops the water temperature in the dripper, and lower temperature hurts extraction efficiency, which could lead to under-extraction. The other is that once all the carbon dioxide has escaped, the flow becomes much faster, so the contact time between coffee and water shrinks, which again reduces extraction efficiency and makes the coffee prone to under-extraction.

Experimental Verification

So is that really the case? Today FrontStreet Coffee will verify it with an experiment.

The comparison is simple. FrontStreet Coffee brews two pots with different blooming times and compares their taste and extraction yield to see whether the yield really drops. Readers who follow FrontStreet Coffee's posts will know that we recently shared an article on the difference between a 30-second and a 60-second bloom. In that piece we brewed three sets for comparison, and although the three used beans of different roast levels and freshness, the results were the same every time: the set with the longer bloom had a slightly higher extraction yield than the set with the shorter bloom.

Some might think that the difference in blooming time was simply not large enough. So today FrontStreet Coffee widens the gap, comparing a 30-second bloom against one as long as 1 minute and 30 seconds (any longer would be unnecessary), to see whether the claim holds: that too long a bloom actually lowers extraction yield. For this experiment, FrontStreet Coffee chose FrontStreet Yirgacheffe Gedeb from the FrontStreet Coffee menu. It has been 10 days since roasting, putting it in its optimal flavor window while it still holds some carbon dioxide, which perfectly demonstrates the effect of different blooming times. The parameters were as follows: coffee 15.6g, water 225ml, grind at 80% passing a No. 20 sieve, water temperature 92°C, three-stage pour.

Experimental Results

We will skip the brewing process, since apart from the time and the blooming duration everything was essentially the same, and go straight to the results. On taste, the 30-second bloomed Gedeb performed exceptionally well: balanced flavor, a smooth mouthfeel, prominent character with white florals, lemon, and berry aromas, and a long finish. The 1-minute-30-second bloomed Gedeb did exactly what FrontStreet Coffee expected, coming out slightly better than the 30-second version. Although the difference was not large, its flavors were more prominent and its body fuller.

Measuring extraction yield confirmed this. 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 flow rates were identical: both sets of subsequent pours finished in the same amount of time, with no acceleration from excess gas release. The water temperature was the same too: both pots started at 92.6°C, and by the second pour they read 91.4°C (30 seconds) and 90.9°C (1 minute 30 seconds) respectively. So although the blooming time differed by a full minute, the temperature difference was only 0.5°C, which would not have a significant effect on extraction.

Conclusion

These results show that extraction yield did not fall as time increased. On the contrary, it improved slightly. So does that mean an overly long bloom never causes under-extraction?

Not necessarily. Under certain specific conditions, an excessive bloom can indeed lead to under-extraction, though those situations are usually quite extreme. For example, if the blooming time runs longer than 1.5 minutes, if the ambient temperature is even lower than it was here, or if the gooseneck kettle's heat retention is not as good. In those cases the water temperature after blooming would be much lower than preset, reducing extraction efficiency and ultimately leaving the coffee with a lower extraction yield than a 30-second bloom would give.

Even then, that only makes the extraction yield lower than with a 30-second bloom, not necessarily under-extracted. From the yields FrontStreet Coffee measured, we can calculate that even when differences appear, they will not be large enough to cause under-extraction. If under-extraction really does occur, then beyond an excessive bloom, it is very likely that the original brewing parameters were not extracting the coffee sufficiently to begin with, so a slightly lower water temperature pushes it into under-extraction.

In summary, an excessive bloom does affect extraction yield, but whether that effect is good or bad depends on the circumstances.

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FrontStreet Coffee Recommendation

Blooming, and the whole question of extraction, is easiest to observe on a clean, aromatic washed coffee. The FrontStreet Washed Gotiti, a typical Yirgacheffe, is a good choice: it carries jasmine florals, lemon acidity, and berry notes, and it is one of the friendliest starting points in specialty coffee. The FrontStreet Natural Huakui, from the Sidamo region and processed with a traditional sun-dried method, brings berry, floral, jackfruit, melon, and honey notes for a fruitier comparison.

For a lower-acid option to round out a tasting, the FrontStreet Brazil Cerrado Red Bourbon is an entry-level single origin from a well-known Brazilian region, with the classic cream, peanut, and cocoa flavors of a Brazil bean at a friendly price, while the FrontStreet Queen Estate is grown at higher altitude from the rare Yellow Bourbon variety, adding butter, sunflower-seed, macadamia, and almond notes with a sugarcane-like sweetness.