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The Real Science Behind The Coffee Bloom

If you are tired of brewing stagnate, flat coffee in your own home, and you would like to learn how to make a cup of coffee that tastes every bit as great as a cup from your local coffee house, all you have to do is learn a little of the science behind brewing that perfect cup of coffee. While that may sound difficult, it is actually much easier than you think.

Increasing your knowledge about the processes at work will help you change that sour cup of coffee into a perfectly tasting cup that will impress even the most stalwart coffee snobs that know. One of the keys to improving your coffee brewing skills, is understanding coffee bloom.

Coffee-Bloom---Main

What Is Coffee Bloom?

If you hang out with true coffee aficionados or enjoy frequenting coffee shops, chances are you have heard of the term, coffee bloom. But what is it? To put it simply, the coffee bloom is the fast release of gas that occurs when hot water comes in contact with the coffee grounds.

Coffee Bloom Causes

The bloom is caused by the roasting procedure. Whenever coffee beans are roasted, the heat causes carbon dioxide (CO2) to become trapped in the bean. Once the roasted process is completed, the beans then begin to slowly discharge these gases a little bit at a time in a process known as “degassing.”

If you are using coffee roasted in within a ten day time frame, much of the carbon dioxide will be retained by the beans even though the degassing process has begun. As soon as the beans are ground, the gases begin to escape much more quickly. When hot water touches the ground coffee, they immediately begin to purge themselves of the carbon dioxide creating the bloom effect.

Fresh Roasted Versus Ground Coffee

While the normal loss of carbon dioxide and other gases begins as soon as the roasting process is complete, it will take a couple of weeks for all of the gas to escape following the roast. These gases are what brings the flavor to our cups of coffee meaning that, ideally, you want to make sure that as many of these gases remain in the beans for as long as possible.

When coffee is ground, the gases are able to escape much more easily. This is why most serious coffee drinkers always grind their coffee just before they use it.

Variables That Affect Bloom

There are many variables that can affect the bloom. The following factors impact the rate at which the gas is lost in the beans after they have been roasted.

Temperature – The hotter the area in which the beans are stored the faster the gas will escape from the beans. Ideally, you want to try to store the beans in a cooler environment away from anything that generates heat such as lighting in your kitchen or your stove.

Humidity – The dryer the area, the more gas that will escape from the beans. Of course, high humidity levels will encourage mold and other fungi to grow. Ideally, you want to find the perfect balance in your humidity levels to protect the gas and shield your beans from mold.

Roast level – The type of roast will have a large influence on bloom. Darker Italian roasts, for example, undergo much less degassing compared to other types of roasts.

Bean Origin – The origin of the coffee bean can also impact the bloom as some coffees are known to undergo more degassing than others.

Bean Hardness – The harder the bean, the more difficult it is for the carbon dioxide to make its way through the bean and escape.

How To Bloom

The basic process for coffee blooming is to pour hot water over top of the coffee so they become damp but do not drain a minute or two before brewing your coffee. However, how you do this depends on the type of coffee maker you use.

Pour Overs

Pour very hot water on the coffee in a circular motion beginning from the outside and then working your way into the middle. Only use a little water. You want the coffee to become soaked but not drip through the filter. Allow it to set for about one minute before you make your cup of coffee.

French Presses

For French Press owners, slowly pour a small amount of hot water over coarsely ground coffee. Let the bloom stand for about 20 seconds, then stir it with your spoon to be sure all the grinds come in contact with the water. Then complete your normal brew regime.

How to Brew Coffee With a French Press

The Complete Guide to French Press Coffee

There's a right way and a wrong way to make coffee with a French Press. Here are the techniques, ratios and beans you need to make the perfect cup.

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Automatic Drip Coffee Makers

Place your filter in your coffee maker’s basket and add your ground coffee to it. Add just enough water over the top of the grounds to soak the coffee but not enough that it will drip through the filter. Allow it to set for about 90 seconds and then begin your normal brewing cycle on your coffee maker.

Remember, when you pour hot water over top of your coffee grounds, you should see the bloom form. If nothing happens to your coffee, it is most likely stale and will not produce a good, full flavored cup of coffee.

Now that you understand a little of the science behind bloom, you can now talk shop with even the most dedicated coffee aficionado. Above that, you can now start to brew a better tasting coffee right in your own home by following the above blooming techniques no matter if you are using fresh roasted or ground coffee.

Coffee-Bloom---Pinterest

  • Great Post Matt! I have been using a Chemex for a couple months, when I ran out of filters for it and used my old drip machine UGH! you can tell the difference! I always “Bloom” with the Chemex (Filters are on order!) and really appreciate all the tips you provide!!

    • Matt Giovanisci

      Thanks Rick! How did you find out about this site?

      • I saw some of your posts in Fizzle.co

        • Matt Giovanisci

          Glad to see a fellow Fizzler!

  • Hey Matt! Heard about you on Fizzle too. Love what you’re doing! I’ve been brewing good stuff at home for years, but you’re helping me take it to the next level. Good stuff, thanks!

    • Matt Giovanisci

      Thanks, John! I’m glad you’re enjoying the site. Fizzlers are the best!

  • Rakel

    I am so gonna try this! We just have bought some new fresh christmas coffee, which will be perfect for trying this out!

    • Matt Giovanisci

      Sweet! I bloom every morning. About to do it soon, too 🙂 Let me know if it makes a difference for you.

      • Rakel

        I am in that lucky position that I’m not the one makes the coffee in the morning, i just drink it 😉 But our mocha master makes an excellent brew! But I will let you know then I try it 😉

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  • heavenandearth

    How long do you recommend blooming the coffee in a Bonavita Full Immersion Dripper?