Understanding Coffee “Bloom”
One of the interesting phenomenons of using fresh beans is the creation of a bloom effect. The “bloom” commonly occurs from fresh roasted coffees. When hot water is poured over the ground coffee, a chemical reaction takes place that causes the release of CO2. Leading to bubbling, like what you see in the image below.
Generally, there are two times you’ll really notice coffee bloom; when brewing with a pour over brew method or when using a French press.
During the pour over brew (using a Hario, Chemex, or etc.) the bloom will occur right away as you add water. This is the reason why many recommend pour slowly to begin with and then stop, to allow the bloom to settle.
Once it has settled, then pouring water into the filter will allow the grounds to create the proper funnel without the gases interfering. When poured correctly (allowing the bloom to settle), the coffee filter will shape the coffee in a V.
When using a French press, the bloom can be much more troublesome. Once hot water has been poured over the ground coffee in a press pot, the coffee begins to release its CO2, causing bubbling. If the roast is extremely fresh, the amount of bubbling could be enough to cause problems during the brew process.
As the plunger is pressed in a French press, the bloom could cause bubbles and coffee grounds to escape into the brewed coffee. A good way to minimize this is to stir the coffee before plunging, breaking the crust and allowing much of the gases to escape.
It’s important to note that the bloom is not all bad. It plays a very important role in the brewing process. The bloom and gases actually infuse the brew with aromas and tastes. Finding the perfect brew means going beyond just figuring out temperature, roast, time – it means understanding how to use the bloom to your benefit and making the most out of every cup.