French Press Coffee Bloom: Does It Really Make a Difference?

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Last updated on November 14, 2023


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Have you ever wondered whether that initial step of blooming your coffee grounds before brewing in a French press is worth the extra time and effort?

Does it truly affect the flavor profile, or is it just another trendy ritual in the world of coffee brewing?

We understand it might be frustrating to see varying opinions on blooming in the French press.

Are you seeking to understand the science behind it and how it influences flavor?

Are you eager to perfect the process and unlock the full potential of your French press brew?

Or maybe you’re just skeptical and looking for answers regarding the necessity of blooming?

After Reading this Article, You Will . . . 

●     Better understand the concept of blooming, and why some opt to include it.

●     Get an in-depth look at blooming variables, techniques, and some common misconceptions. 

●    Learn to optimize the blooming process to elevate your coffee experience, should you choose to incorporate it.

●     Be equipped to decide if French press blooming is right for you.

Whether you're a flavor aficionado, a variable geek, or someone skeptical about the value of blooming, we've got you covered. Let's unlock the secrets of blooming and discover how it can enhance your French press coffee.


The Short Answer

Yes, blooming one's coffee grounds before brewing in a French press can have an impact on flavor, especially for fresh specialty and single-origin coffees that are roasted on the lighter side.

By allowing the trapped carbon dioxide gas (and a few other gases) to escape from the grounds before water saturation begins, blooming ensures a more controlled and even extraction of flavors.

Without blooming, some grounds may initially absorb more water than others. This is because the off-gassing inhibits contact. But with blooming, the gas is removed so maximum extraction can occur sooner, leading to a richer, fuller-bodied cup of coffee with better-developed flavors.

That said, some opt to skip the bloom, so let’s dive into the details and see if the potential difference in flavor is enough to convince you to add the ritual to your brew.

What Is Coffee Bloom and Does It Really Make a Difference in French Press Brewing?

Coffee bloom refers to the phenomenon that occurs when hot water first comes into contact with coffee grounds. Trapped gas—mainly carbon dioxide—is released from the grounds, causing them to expand and "bloom."

As the CO2 is released, the hot water has a harder time penetrating the coffee grounds (leading to a less effective extraction).

Less extraction = less flavor

This becomes a bigger issue with percolation brews (like a pour over), where the contact time between hot water and coffee grounds is already so brief.  

But what about immersion-style brewing techniques (like French press) where the contact time between water and coffee is much more lengthy?

Can a bloom step still improve flavor?

We think so. 

Particularly for lighter roast profiles which contain higher acidity (and often more trapped CO2), blooming helps control and integrate these flavors into a more nuanced balance.

With visual cues and a bit of timing and technique, you can easily bloom your grounds and achieve optimal flavor results.


Why Is Coffee Bloom Beneficial for a French Press?

A proper bloom in a French press can lead to a fuller-bodied, more flavorful cup of coffee. That’s because the process allows for a fuller extraction of soluble compounds.

Non-bloomed coffee might taste thinner, with less developed flavors.

While it's true that immersion brewing soaks the grounds fully, thereby giving the carbon dioxide plenty of time to escape, blooming often provides unique benefits.

Yes, with French press immersion brewing, the CO2 will leave eventually (without blooming), but by incorporating the blooming step, you’ll ensure this happens before full extraction begins.

Without blooming, the saturation process is less controlled.

As water first contacts the grounds, the released CO2 causes uneven wetting. Some particles may absorb more water than others in that initial phase, which will change their rate of extraction.

Blooming mitigates this effect by removing the gas barrier first.

It also expedites the process.

With blooming, rather than waiting passively for gases to release over the full brew time,  the grounds release the CO2 upfront, so maximum extraction can occur sooner.

The Relationship Between Grind Size and Coffee Bloom

Your grind size also plays a significant role in coffee bloom.

The ideal grind size for French press extraction (bloom or no bloom) is medium-coarse. This grind allows for a full and even extraction of flavor from the coffee grounds into the water and prevents over-extraction.

This same medium-coarse grind is also the best choice when blooming because it releases CO2 and facilitates water absorption.

Increasing the surface area of the beans (by grinding) encourages the beans to release more compounds—whether that’s flavor-giving compounds during extraction or CO2 during blooming.

But, there’s a point of diminishing returns. 

Grind too finely, and your grounds will become too tightly packed, creating an uneven saturation that—in the case of immersion brewing—disrupts both extraction and bloom.

Bottom line: just as the medium-coarse grind provides an even extraction (reconciling surface area and density), it will also deliver a balanced bloom.

The Role of Roast Level in Coffee Bloom


Your preferred roast profile can influence the effect that blooming in a French press has on flavor.

Darker roasts tend to be less affected by blooming in a French press due to the extent of the Maillard reaction during roasting. In contrast, lighter roasts with higher acidity benefit more from pre-extraction during blooming.

The Maillard reaction that occurs as beans roast is a complex series of chemical reactions between amino acids and reducing sugars in the coffee beans. This is what gives darker roasted beans their deeper flavor profile. It also affects their composition.

During the Maillard reaction, volatile compounds like carbon dioxide are baked out of the beans. Lighter roasts experience less of this thermal degradation, leaving more CO2 intact post-roast.

Additionally, in darker roasts, the Maillard reaction generates new molecules that alter acidity and other flavors, whereas lighter roasts maintain higher natural acid levels, which the blooming process controls, helping them integrate into the final brew.

Finally, due to their porous nature, dark roast beans release their post-roast gases in a shorter amount of time. So, 4 weeks out, your dark roast beans may have completely off-gassed. 

In short, where darker roasts have already reacted and modified the molecular composition and flavor profile through extensive browning, blooming may have less impact on taste than it does with lighter roasts.

So, the decision to bloom will be influenced by your personal preferences for roast toast level (i.e. it may not be as valuable if you brew dark, especially as more time goes by).

The Relationship Between Coffee Freshness and Coffee Bloom

As you might expect, the freshness of your coffee affects blooming.

As coffee ages, it loses carbon dioxide. Consequently, older coffee doesn't have as much gas to bloom, and might not benefit much from the process. This is especially true of darker roasts.

You can alter your bloom in propotion to the freshness. If you have a bag of freshly roasted coffee beans, consider extending your bloom up to 1 minute. On the other hand, if you’re using coffee that’s as much as 4 weeks old, bring your bloom time down 15 seconds.

For optimal blooming results, use beans that are no more than two weeks post-roast. At 4 weeks, the blooming ritual hits a point of diminishing returns.  


Tips for Blooming in a French Press

At first glance, blooming in a French press may appear more of an art than a science. By implementing these tips though, you will gain control over the process—and increase the likelihood of being able to replicate your results:

Weigh Your Ingredients

For consistent, reproducible results, weigh your coffee grounds and water separately using a digital scale. Measuring by weight rather than volume ensures you’re extracting the same amount from batch to batch.

Start with one of our recommended French press brew ratios.

Then follow the tips below to incorporate blooming.

Ratios And Timing

For the bloom, you’ll want to just cover the grounds: use two parts water to one part grounds. For example, if you are using 15 g of coffee, bloom with 30 ml of water.

Allow 30 seconds for the bloom. During this time, gas escapes from the grounds, forming what's called the "crust." Pay attention to your bloom time for optimal carbon dioxide release.

Pro Tip

The blooming time should be included as part of your usual overall brewing time. For example, if you prefer a 4-minute brew method, the 30 seconds of brewing should be included in those 4 minutes.

Break the Crust with Care

After another 30 seconds, stir gently to break up the crust and fully integrate the freshly wetted grounds back into the slurry. Aggressive stirring could cause aeration that affects extraction.

Add the rest of the water and stir again. For best saturation, give everything another gentle stir halfway through.

Experiment with Grind and Technique

Varying grind size or bloom duration can influence flavor. Play around until you achieve a balanced, nuanced body and flavors that suit your tastes. Keep notes so you can replicate results that you are satisfied with.

French Press Ratios with Bloom 

Brew StrengthRatioCoffeeTotal WaterTotal Steep TimeBlooming
Blooming Time
Strong1:1262 g*750 ml4 min124 ml30 s
Medium1:1550 g750 ml4 min100 ml30 s
Mild1:1841 g*750 ml4 min82 ml30 s

*Measurements are slightly rounded. The measurements given are for making roughly 3 cups of French press coffee (or 750 ml). Remember the amount of water and time used for blooming are taken from the total amounts of water and time. 

So if you want to make 3 cups of strong coffee, you’ll bloom 62 g of coffee with 124 ml of water for 30 seconds. Then add the rest of the water (626 ml) and steep for another 3 minutes and 30 seconds.

Common Coffee Blooming Mistakes

Beware of these common blunders:

  • Neglecting to stir thoroughly after blooming.
  • Using stale coffee that is already depleted of carbon dioxide.
  • Not including bloom time within the total steep time.
  • Relying solely on visual cues to judge a successful bloom. After all, a nice-looking bloom is pointless if it doesn’t improve the cup.


While the differences may seem subtle, French press blooming takes little effort. Especially for experiential brewers focused on optimization.

We hope to have shown you that coffee bloom isn't just a trendy ritual; it's a worthwhile practice that has scientific weight and can indeed impact flavor.

The blooming process is a canvas for experimentation.

Now, that you can explain the science behind it, you’ll just have to try it yourself. So, if you've ever questioned the benefits of blooming in immersion methods, we hope you’ll give it a go!

Ultimately, only your own taste tests will reveal if blooming with a French press gets you one step closer to a flavor profile that you love.

Happy brewing! 



Can You Over-Bloom Your Coffee?

It is possible to over-bloom your coffee. After about 45 seconds, the potential benefits of blooming plateau. Keep it brief and efficient.

Does Coffee Bloom Affect Caffeine Levels?

No, blooming is about flavor extraction rather than caffeine levels.

What to Do If Your Coffee Doesn't Bloom (No Bubbles)?

If your coffee doesn't bloom, you might need to use fresher beans or adjust your grind size to be a bit coarser. There might also be an issue with your water—see below.

How Does Water Softness or Hardness Affect Bloom?

The mineral content of your water can impact the visible bloom effect.

Hard water, with higher amounts of minerals like calcium and magnesium, encourages bigger, longer-lasting blooms.

On the other hand, very soft water might produce less dramatic blooms. However, the appearance of the bloom isn't as important as the extraction factors it provides.

What Specific Flavor Differences Can I Expect Between French Press Bloomed and French Press Not Bloomed?

Bloomed French press coffee typically has a richer, more complex flavor profile—especially with lighter roasts. The process allows for a fuller extraction of soluble compounds that contribute to a balanced, nuanced cup.

Non-bloomed coffee might taste thinner, with less developed flavors.


Anderson, B. A., Shimoni, E., Liardon, R., & Labuza, T. P. (2003). The diffusion kinetics of carbon dioxide in fresh roasted and ground coffee. Journal of Food Engineering, 59(1), 71-78.

Craft Coffee. (2015, June 27). French Press Brew Guide | Craft Coffee. Craft Coffee Subscriptions. Retrieved October 5, 2023, from

Cardelli, C., & Labuza, T. (2001). Application of Weibull Hazard Analysis to the Determination of the Shelf Life of Roasted and Ground Coffee. LWT - Food Science and Technology, 34(5), 273-278.

Moreira, A. S., Nunes, F. M., Simões, C., Maciel, E., Domingues, P., Domingues, M. R. M., & Coimbra, M. A. (2017). Transglycosylation reactions, a main mechanism of phenolics incorporation in coffee melanoidins: Inhibition by Maillard reaction. Food Chemistry, 227, 422-431.

North Star Coffee Roasters. (2022, November 19). Demystifying the Coffee Bloom – North Star Coffee Roasters. North Star Coffee Roasters. Retrieved October 5, 2023, from

Why Must We Bloom Coffee in a French Press? : r/Coffee. (2020, March 30). Reddit. Retrieved October 5, 2023, from

About the author, James Allen

James is a seasoned coffee enthusiast, dedicated home roaster, and brewing aficionado with over 15 years of immersion in the world of coffee. His passion for the bean has taken him on an incredible journey, from assisting locals in establishing farm-to-cup micro-roasteries and cafes in Bali to pioneering one of the first blockchain projects aimed at enhancing traceability in coffee supply chains. Based in Japan, James spends a significant portion of his year embarking on travels to coffee-producing countries with a recent focus on the rapidly advancing Thailand arabica scene.