Coffee Bloom Duration: Why Must Hand-Drip Coffee Bloom for Exactly 30 Seconds?

"What's the difference between a 30-second bloom and a 60-second bloom in coffee?" This was a question that a friend asked FrontStreet Coffee yesterday. And you know what? That's actually a really interesting question!

As we all know, blooming is an essential step in pour-over coffee. The specific process involves pre-infusing a small amount of hot water to moisten the coffee grounds before the main pour, followed by a pause of about 30 seconds. In coffee preparation, this step significantly improves extraction efficiency and increases the amount of dissolved coffee compounds. Simply put, it makes the brewed coffee taste richer. FrontStreet Coffee specifically conducted tests on this: using the same coffee beans and extraction parameters, coffee with a 30-second bloom had a much higher extraction rate than coffee without blooming, and the difference in flavor was so distinct that even beginners could easily distinguish between them. This shows how significant the impact of blooming is on pour-over coffee.

"But if what FrontStreet Coffee mentioned above is true, wouldn't a 60-second bloom be even better than 30 seconds?" That's why our friend asked the initial question yesterday. Excellent! Since our friend has sincerely asked, FrontStreet Coffee will conduct a brewing comparison to share with everyone what exactly the difference is between coffee with a 30-second bloom and a 60-second bloom.

Brewing Experiment

In this brewing test, FrontStreet Coffee will use three batches of coffee beans at different freshness levels for comparison! These include fresh coffee beans just 3 days from roasting, prime flavor period beans 15 days from roasting, and beans 30 days from roasting. Then FrontStreet Coffee will brew two pots of coffee with each bean batch – one with a standard 30-second bloom and another with a 60-second bloom. Finally, we'll compare the differences by measuring extraction rates and tasting the flavors. Since all three batches are medium-light roasts, all parameters except bloom time remain identical! As follows:

• Coffee amount: 15g
• Brewing water temperature: 92°C
• Coffee-to-water ratio: 1:15
• Grind size: Ek43 setting 10, 75% through #20 sieve, fine granulated sugar texture
• Brewing method: Three-pour technique
• Auxiliary tools: Gooseneck kettle with shower head (to minimize human impact on brewing)

We'll skip the detailed brewing process description. After FrontStreet Coffee brewed the coffee, we conducted tasting and extraction rate measurements, with the final results as follows:

3-day roast batch:
30-second bloom extraction rate: 19.95%
60-second bloom extraction rate: 20.33%

15-day roast batch:
30-second bloom extraction rate: 20.21%
60-second bloom extraction rate: 20.49%

30-day roast batch:
30-second bloom extraction rate: 20.37%
60-second bloom extraction rate: 20.58%

As can be seen, regardless of the batch, the 60-second bloom indeed has a slightly higher extraction rate than the 30-second bloom, but the difference between them is smaller than most people would imagine. The same applies to flavor differences – coffee with a 60-second bloom tastes slightly richer than with a 30-second bloom, but not significantly so.

Understanding the Results

Although both involve a 30-second difference, the experimental results of "0 seconds vs 30 seconds" and "30 seconds vs 60 seconds" are vastly different. The former comparison can be accurately distinguished by beginners in blind tasting, while the latter requires careful tasting by experienced baristas to distinguish between the two (except for the first batch, which shows more obvious differences). The reason for this is that the blooming effect we need is largely completed within the brief 30-second period.

Why Pour-Over Coffee Needs Blooming

The reason blooming improves coffee extraction rate is mainly because it allows the coffee grounds to expand and release carbon dioxide accumulated during the roasting process.

Coffee extraction occurs through concentration gradients! When hot water comes into contact with coffee grounds, the flavor compounds in the grounds transfer to the lower-concentration water due to the concentration difference. However, a problem we face in this process is that water cannot immediately penetrate into the interior of the coffee grounds to access the internal flavor compounds. This is because carbon dioxide within the coffee grounds is rapidly expelled upon contact with hot water, which slows down the water's penetration into the interior of the coffee grounds. If large amounts of water are poured for extraction before the coffee grounds are fully moistened, much of the hot water won't be able to fully extract the flavor compounds from the coffee.

Therefore, we need the blooming process to complete the release of carbon dioxide. By pre-wetting the coffee grounds with a small amount of hot water, carbon dioxide is released, allowing water to penetrate internally. This way, subsequent hot water can better dissolve the flavor compounds within the coffee grounds, making extraction more uniform and efficient. However, the time required for hot water to complete this task varies depending on the state of the coffee beans and the parameters used. Some friends may have already noticed from the experiments shared by FrontStreet Coffee that the extraction rate difference between the two pots in the first batch is the largest, and the difference between coffees becomes progressively smaller in subsequent batches.

This is because the first batch used the freshest coffee beans with the highest carbon dioxide content, requiring longer blooming time to release the carbon dioxide from the coffee grounds, which is why the difference between the two pots in the first batch is relatively large. Additionally, factors like roast level, density, and extraction parameters all influence the required blooming time. However, checking each factor individually to find the appropriate bloom time would be too difficult for beginners. Therefore, FrontStreet Coffee generally recommends that beginners start with a "30-second" bloom time, which is a relatively safe blooming approach. It's neither too short (insufficient degassing) nor too long (wasting time). With the right parameters, this time still allows for adequate coffee extraction.

Once you can consistently brew a delicious cup of coffee, it's never too late to start learning advanced knowledge. Of course, if you have the need right now, you can directly click the "Portal" to learn more~

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FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

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