What is coffee bloom and why does it matter?

Yker Valerio
November 8, 2022
What is coffee bloom and why does it matter?

Serving pour overs at a café only recently became popular as more customers began searching for alternatives to traditional espresso and drip coffee. 

As a result, a number of high-end coffee shops, cafés with a specialty coffee approach, and large coffee brands are considering filter coffee as an essential part of their offerings. 

One of the most essential details when brewing filter coffee is the bloom. Coffee bloom helps to prevent sourness in the cup, and can provide signals about the coffee’s freshness, roast, and more. 

More so, specialty enthusiasts are taking a greater interest in brewing fine coffees at home, and paying attention to every detail. Many have begun to wonder what factors in a roast produce a coffee bloom, and whether it affects the final flavour in the cup. 

To learn more about coffee bloom, I spoke with Gerson Otzoy, owner of Fat Cat Coffee House, and Kleidys Ramírez, the founder of Melosa Café.

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An image of a barista serving pour over coffee in a cafe in an article about coffee bloom and why coffee bloom is important in brewing coffee.

What is coffee bloom?

Essentially, a bloom is when roast coffee grounds release carbon dioxide (CO2) and oils as they come into contact with water. 

This usually happens during the pre-infusion stage of the brewing method. The reaction has a characteristic foam and group of bubbles that appear on the surface once the water is poured over the grounds.

A bloom is easiest to observe when brewing coffee using immersion and pour over methods. It occurs because coffee beans contain CO2, which is trapped inside during the roasting process. 

Many baristas and aficionados consider the coffee bloom to be of great interest. 

“This may be because it is an excellent sign of freshness,” explains Gerson, who has roasted his own coffee in Antigua, Guatemala, for three years. “It also informs us when a coffee is losing freshness because as coffee ages, it produces a weaker bloom.”

Kleidys, who is also the head roaster at Melosa Cafe, explains that “brewing fresh coffee requires a pre-infusion to start hydrolysis, which is the breaking of organic compounds through water.”

“Bloom provides us with a reading of coffee degassing,” Gerson explains. “The older the coffee, the less gas it will release, and stale and cardboard flavours tend to appear in the cup.”

The intensity and duration of a coffee bloom can vary depending on several factors. These include coffee freshness, bean density, roast degree, grind size, water temperature, and the coffee-to-water ratio.

After coffee is roasted, the beans continue to release CO2 for days and even weeks. For roasters, degassing is essential and plays a significant role in developing a complex and rich aromatic profile.

Notably, it is common to find instructions on coffee bags indicating bloom as a step to brewing coffee effectively. One of the most common ratios for blooming is a 2:1 water-to-coffee ratio, but other well-known recipes differ, such as Tetsu Kasuya’s 4:6 method and Elika Liftee’s V60 method.

In both cases, they use more water to wet the coffee bed during the pre-infusion: between 3:1 and 4:1.

An image of a coffee roaster using a large-scale roaster to roast coffee in an article about coffee bloom and why coffee bloom is important in brewing coffee.

What variables affect coffee bloom?

Gerson explains the most crucial variable for bloom is coffee freshness. 

“It will not matter what roast profile the coffee has. If a coffee is fresh, a bloom will appear,” he says. 

However, coffee freshness refers to at least two different factors: the storage time after roasting, and the time between grinding the beans and brewing them.

Proper packaging after roasting is essential, as it allows the beans to release gases. If beans are unable to release these gases, they may negatively affect the coffee’s taste and aroma. 

In addition to roast freshness, the roasting degree matters too. Light roasts show a weaker bloom than dark roasts. This is because dark roasts build more CO2 during a longer roast process, resulting in a larger bloom.

According to Chahan Yeretzian, Head of the Coffee Excellence Center at ZHAW, once coffee is ground, aroma loss and oxidation are accelerated, mainly due to the opening up of the pores and the much-increased surface areas

In short, the coffee bloom is more vigorous in freshly roasted and ground coffee, where oxidation has been minimal, and carbon dioxide is still present.

An image of a barista in a cafe serving pour over coffee in a v60 with a multilayer LDPE coffee bag in background in an article about coffee bloom and why coffee bloom is important in brewing coffee.

Why does a bloom matter?

“Coffee bloom is the language the beverage speaks, telling us how fresh it is,” Gerson says. 

“When coffee has no has, it begins to lose its characteristic water resistance, which is why some brews produce weak extractions,” he adds. 

“For me, bloom is a synonym of freshness and vitality in coffee flavours,”Gerson says. “At least 15 days after roasting, many coffees will not bloom and they begin to run against the clock towards staleness.”

Baristas also use bloom for a number of reasons, such as to enhance brewing results by preventing the unpleasant sourness of CO2 from appearing in the cup. 

This can help produce an even and rich extraction of the aromatic compounds that are perceived while drinking coffee. 

“Bloom occurs in all extraction methods,” Gerson explains. “However, it may not be visible in all of them.”

For instance, he explains espresso that was roasted at least six days previously may get better results, while coffee roasted three days previously may be better suited for pour overs. 

“However, that’s a decision that every barista or coffee shop has to make.” says Gerson. 

Storing roast coffee in high-quality packaging is essential to assure baristas and customers have a superior brewing and coffee-drinking experience.

Keeping coffee sealed and in a cool place, away from humidity and light, is common practice. 

Proper storage also ensures that carbon dioxide is released gradually, allowing the coffee beans to maintain their freshness for longer.

At MTPak Coffee, we offer roasters the option to fit their coffee bags with fully recyclable, BPA-free degassing valves.

In addition to being versatile, lightweight, and affordable, our valves can be fitted to our entire range of sustainable coffee packaging options.

Roasters can choose from renewable materials such as kraft paper, rice paper, or multilayer LDPE packaging with an environmentally friendly PLA lining, all of which minimise waste and contribute to a circular economy.

More so, we give our roasters complete control over the design process by allowing them to build their own coffee bags.

Our design team is available to help you create the ideal coffee packaging.

Plus, we are able to custom-print coffee bags using innovative digital printing technology, with a quick turnaround time of 40-hours and 24-hour shipping time.

MTPak Coffee also offers low minimum order quantities (MOQs) to micro-roasters who are looking to remain agile while showcasing brand identity and a commitment to the environment.

For more information on sustainable, custom-printed coffee packaging, contact our team.

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