Bloom is a quick bubbling up of carbon dioxide and coffee grounds that occurs when freshly roasted coffee is brewed. Giving your coffee a half minute to bloom, depending on how recently it was roasted, will enhance its flavors.
Coffee gives off carbon dioxide for about two weeks after it is roasted. This process is called “degassing.”
The most gas is released shortly after roasting, especially in the four hours immediately following roasting. Carbon dioxide continues to escape from the beans for 14 days, with the amount of gas being released slowly declining over that period.
When coffee beans are ground, the rate at which carbon dioxide is released increases quickly. Grinding increases the coffee’s surface area, which in turn increases how much gas the beans can release. (This is why fresh coffee should only be ground shortly before brewing it.)
Water further accelerates the release of carbon dioxide, as is evidenced by the bubbling up of gas when water first contacts the grounds of recently roasted coffee. This occurs during the initial stages of brewing and is called “blooming;” it indicates that the coffee is fresh. Blooming is a quickened degassing brought about by pouring a little water over grounds.
Let Coffee Bloom
Letting coffee bloom is easy and requires no additional equipment. Simply pour a little water on fresh coffee grounds, and give them 30 to 40 seconds to bubble up. Once the bloom is over, continue with the rest of the brewing process. When dampening the grounds, either measure out 2 grams of water for every 1 g of coffee, or use just enough water to get the grounds slightly wet, depending on how exact you like to be.
Letting carbon dioxide escape will improve a coffee’s flavor in two ways.
- First, carbon dioxide has a sour taste. If grounds are not allowed to bloom before brewing, the gas will infuse a sour taste into the coffee.
- Second, carbon dioxide repels water, which interferes with the brewing process. Water can freely extract the aromatics and oils in coffee only after carbon dioxide has escaped.
As long as gas is trapped in the grounds, it will prevent the water from extracting solubles and infuse a sour taste into the finished beverage.
The next time you brew freshly roasted coffee at home, let your grounds bloom. Giving them a chance to breathe will ensure that you capture all of the fine notes of the coffee without the sourness that carbon dioxide produces.
P.S. We’re not always serious about everything in coffee – if you have a few minutes to spare, watch this Conan skit about coffee taken too seriously.