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14.10.20

To Bloom or Not To Bloom

Coffee-bloom

Even if you’ve just gotten into coffee, there’s a good chance you’ve heard of a ‘coffee bloom’ and have some vague idea of what it is and why people do it.

Having recently surveyed over 350 coffee brewers over Instagram and asked; ‘Do you bloom for immersion methods?’, we received a very conflicting and mixed set of replies. 244 of 369 people voted no—which prompted an investigation.

So we decided to conduct a few experiments and publish our findings to hopefully provide some insight and helpful data into the discussion. But before we get into when to and when not to bloom, let’s quickly recap on our knowledge of coffee blooming.

Bloom for immersion poll

What is a coffee bloom?

 

A coffee bloom is the rapid release of gas (mostly carbon dioxide) as hot water comes into contact with ground coffee. It gets its name from how the coffee bed appears to bloom like a flower as the gas bubbles escape.

Carbon dioxide (CO2) is a byproduct of the roasting process. It is formed during the break down of complex carbohydrates and chemical changes inside the bean at high temperatures. The darker the coffee is roasted, the more residual CO2 it will retain.

Roasted coffee beans naturally releases CO2 over time, but the process can be sped by up crushing the cell walls of the bean (grinding the coffee) and indefinitely by adding hot water (brewing the coffee).

 

Why do you bloom coffee?

 

Blooming helps prepare the coffee bed for extraction by allowing most of the COto escape. Water cannot penetrate the coffee grounds efficiently while CO2  is escaping, so the intention of a bloom is to provide space for water to efficiently extract soluble compounds in the coffee.

By doing so, blooming can encourage evenness of extraction, extraction efficiency, and help reduce channeling – but not all brew methods require a bloom.

 

How do you bloom coffee

 

Blooming coffee varies from method-to-method and recipe-to-recipe. Some methods require blooming, while others don’t. Blooming is performed at the beginning of the brewing cycle. The general process involves pouring a small quantity of water (approximately 2 to 3 times the amount of coffee you’re using) over ground coffee, and allowing some time (approximately 30 seconds) for the CO2 to escape. It can sometimes be beneficial to stir or swirl the slurry to help saturate all the coffee grounds. 

Which methods require blooming?

 

Blooming is subjective from method-to-method, so to make it simpler, we’ve separated them into two main categories of brewing; Percolation and Immersion. 

Percolation refers to methods whereby coffee is brewed and simultaneously passed through a porous material or filter (such as pour over).
Immersion refers to methods whereby coffee is fully immersed or steeped in water (such as French Press). 

Blooming and percolation

 

Blooming for percolation methods is highly recommended as it helps increase solubility and extraction efficiency. As we mentioned earlier, water cannot penetrate the coffee grounds while CO2 is escaping—the bubbling CO2 acts as a repellant, causing some of the water to bypass (not come in contact with) the coffee. 

This is usually difficult to mitigate later in the brew and will likely result in an uneven, unpredictable, and diluted coffee. Theoretically, the best possible bloom will involve the minimum amount of water needed to saturate the dose entirely. 

We suggest using a gooseneck kettle as it will give you more precision over your pour. You may wish to swirl or gently stir the slurry with a spoon to help bloom efficiency.

Below are some experiments we conducted showing the difference between bloom vs no bloom on the Cafec Flower Dripper. The experiment aims to reflect the effect that blooming or not blooming can have on coffee strength (TDS) and extraction (EY%) on percolation methods.

The exact same coffee, grind setting, and recipe were used (with the exception of the bloom) to most accurately contrive results. It is not an indication of the quality of coffee, rather a representation of cause and effect.

No bloom
Bloom

 

Sample EY Total brew time TDS EY%
1 206.5 2.06 1.19 16.38
2 206.5 2.04 1.13 15.56
3 204 2.06 1.15 15.83
4 207 2.08 1.14 15.73
5 204.5 2.05 1.16 15.81


Recipe: 15:250 / Flower Dripper (plastic)

0:00 pour up to 240 grams in concentric circles

 

Sample EY Total brew time TDS EY%
1 204 2.06 1.21 16.46
2 205 2.08 1.2 16.4
3 205.5 2.08 1.19 16.3
4 207 2.07 1.19 16.42
5 204.5 2.05 1.2 16.36


Recipe: 15:250 / Clever Dripper (plastic)

0:00 pour 40 grams
0:30 pour up to 240 grams in concentric circles

Blooming and immersion

 

In principal, a bloom is not required for immersion. Unlike percolation methods which have an outlet for brewed coffee, immersion is entirely closed. There is no where for which water can bypass the coffee—making the bloom redundant. Blooming still occurs during immersion, just on a much bigger scale. Think of an immersion as one giant bloom.

Adding a bloom to an immersion is not discouraged, but it adds an extra variable in your routine which may or may not have any direct benefit. It also opens up more possibility for error and inconsistency in your brew which could have otherwise been avoided.

Below are some experiments we conducted showing the difference between bloom vs no bloom on the Clever Dripper. The experiment aims to reflect the effect that blooming or not blooming can have on coffee strength (TDS) and extraction on immersion methods.

Again, the exact same coffee, grind setting, and recipe were used (with the exception of the bloom) to most accurately contrive results. It is not an indication of the quality of coffee, rather a representation of cause and effect.

No Bloom
Bloom

 

Sample EY Total brew time TDS EY%
1 206.5 4.46 1.06 14.59
2 207.5 4.45 1.06 14.66
3 207.5 4.46 1.05 14.53
4 206 4.44 1.06 14.56
5 206.5 4.46 1.07 14.69


Recipe: 15:250 / Clever Dripper

0:00 pour 250 grams
2:00 break crust
4:00 start draw down

 

Sample EY Total brew time TDS EY%
1 207 4.57 1.16 16.01
2 208 4.53 1.1 15.25
3 208.5 4.49 1.08 15.01
4 209 4.48 1.11 15.47
5 206 4.48 1.1 15.11


Recipe: 15:250 / Clever Dripper

0:00 pour 50 grams
0:30 pour to 250 grams
2:00 break crust
4:00 start draw down

To Summarise

 

Blooming and not blooming can have considerable impact on the Total Dissolved Solids (TDS) and extraction efficiency of brewed coffee.

In our percolation experiment, we saw that blooming helped increase extraction and uniformity across all five trials.

In our immersion experiment, we saw that blooming also helped increase extraction, but resulted in more inconsistency. 

We’re not entirely sure why blooming helped increase extraction in our immersion experiment, we suspect it may be due to extra agitation and a fresh cycle of water – if you have any insight here please get in touch.

Nonetheless, based on the statistics we would recommend blooming for immersion only if you’re not concerned with consistency and repeatability—in which case you’ll benefit from a higher extraction. 

If you’ve had differing or similar findings, or if you have any questions we’d love to hear from you. You can reach us on Instagram quite easily or you can use the contact form

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