Blooming of coffee is essentially the release of gases trapped in roasted beans when hot water comes in contact with them. 

This leads to expansion of the coffee sitting in your dripper and often bubble. 

What causes the bloom? 

When coffee beans are roasted, the organic matter of coffee is heated up and releases carbon dioxide (also called degassing). 

When coffee is freshly roasted, it is left for degassing for nearly 48 hours before it is packed for shipping. 

The coffee continues to degass for almost 10 days since roasting and that is the reason you observe degassing valves in most of the packaging that helps release the CO2 through a one-way passage. 

Adding hot water to this roasted coffee causes the immediate release of most of the carbon dioxide. Thus, Blooming. 

Why Blooming is essential? 

a) Blooming helps release the CO2 trapped in beans and thus prevents the CO2 from infusing into coffee that might give it a sour taste. 

b) Blooming helps make space for water to pass though coffee evenly and thus leads to a better extraction quality. 

An indicator of freshness of coffee.

Blooming is an indicator of freshness of coffee. If the coffee does not bloom upon adding hot water to freshly ground coffee, it could indicate three things: 

a) Coffee is not fresh and has degassed already before it reached to you. 

b) Coffee was not sealed properly that lead to faster degassing. 

c) Your beans are over roasted. 

Thus, it is usually recommended to buy the coffee in whole bean form and grind it just before brewing. This will give the best extraction and texture to your coffee. 

How to Bloom? 

To bloom coffee, you need to start pouring at the centre of your coffee and move spirally outwards. Pour about 30 -40 ml of water to 16 grams of coffee and wait for the coffee to bloom for about 30-40 seconds. 

Avoid over-pouring the water on coffee bed as it may not allow CO2 to release freely. 

For best to prepare a pour over coffee, refer to our article on MASTERING POUR OVER. 

Cheers