Blooming or preinfusion: how coffee "blooms" during preparation


As you read above, coffee blooms are a visible reaction of carbon dioxide escaping from the coffee. Why is CO2 in coffee at all and how did it get there? Carbon dioxide is produced as a by-product of roasting. Green coffee is heated in the roaster and gradually during the roasting process, many chemical and physical changes occur to each roasted coffee bean. Each bean is made up not only of caffeine, but also acids and sugars. As it is heated, these chemical compounds change, new ones are formed and some disappear. One of these changes is the formation of the compound CO2.

Thecarbon dioxidethus formed is graduallyreleased from the roasted coffee bean. It escapes for several days after roasting. Mostly, however, when the coffee is freshly roasted. When roasted coffee is ground, CO2 is still present in every particle of ground coffee. Ground coffee degasses faster. Unfortunately, in addition to carbon dioxide, this also applies to other gases that are desirable to us and mediate coffee's unique aromas. That's why the most fragrant and tasty coffee is always that of freshly ground beans.


Coffee that contains CO2 is not ready for extraction. Thecarbon dioxideit contains wants to escape and thus prevents the coffee from being extracted. It is best squeezed out of the coffee beans by water. That is why, whenwe first pour the coffee, we see the carbon dioxide escape. The coffee gains volume, forms bubbles on the surface, seems to bloom. So it's important to give the coffee some time to bloom so that the remaining carbon dioxide leaves the ground coffee and so that nothing impedes the transfer of flavours - extraction - from the ground coffee into the cup. The un-escaped CO2 in the coffee is a barrier to the coffee's contact with water. Simply put, it gets stuck in the coffee. It prevents the water from getting to all the components of the coffee that we want to extract into it, and thus into our cup.


So-called blooming in coffee brewing usually lasts around 30 seconds. The ground coffee is poured with a small amount of water, just enough to keep all the ground coffee particles wet. This ensures that water reaches each one and that the coffee is thoroughly degassed. However, the exact degassing time varies slightly depending on several factors. The age of the coffee since roasting, the roasting style, the fineness of the grind and the variety of coffee plant all play a role.

When preparing coffee from beans that have been roasted completely freshly, for example, four days ago, the optimum time for bloom may be 45 seconds. If we are making coffee that has been on the shelf for more than two weeks, 20 seconds may be all we need for blooming. Thetime will be longer for lighter roasted and coarser ground coffees. Therefore, blooming is more pronounced and significant when preparing filter coffee. For espresso, finer grinds and slightly darker roasted coffees are used, and it is recommended to use them for espresso around day 15, when their flavours are already calmed and balanced after roasting, as well as being more degassed.


In professional lever coffee machines, you may encoun ter asystem of preinfusion, i.e. blooming. Although in this case the bloom of the coffee is not so pronounced and visible, it has its own justification in this method of coffee preparation and helps to improve the extraction process. In filtered coffees the bloom is visible and especially in freshly roasted coffees with a higher CO2 content. Blooming thus becomes an indicator of the freshness of the coffee. When your coffee is not blooming, it does not contain much gas, so it is stale. Along with the missing carbon dioxide, such coffee will also lack the flavours and aromas that we look forward to when drinking coffee.


Therate of gas leakage can be influenced bystorage. A roasted coffee package that is exposed to more heat (for example, if left in the sun) will release gases, including CO2, more quickly. However, high temperatures from direct sunlight will also negatively affect the desired properties of the coffee. Therefore, keep the coffee in a shaded place. In addition to the heat in the environment, the temperature of the water when watering accelerates the release of CO2. Pre-infusing coffee with water at a higher temperature promotes the escape of carbon dioxide, whereas cooler water takes longer.


The usual guide to a properly executed blooming is to keep to the average timeset for blooming, i.e. 30 seconds. Water the coffee with hot water so that all the coffee is sufficiently moist. The ratio of coffee to water volume for preinfusion is most often1:2 or 1:3. This means that for a 15g batch of coffee, we use 30 - 45g (or ml) of water when blooming. After the bloom period, we continue pouring water for extraction according to the recipe used.