The Role of Coffee Blooming, What Gases are Released, and How Much Water to Use

What is Bloom?

Bloom is a step in the pour-over coffee making process.

When we add water for the first time, we perform the "bloom." We first pour hot water twice the weight of the coffee grounds, then stop. This means that if we want to brew 15 grams of coffee grounds, we'll pour 30 milliliters of hot water. If your coffee grounds are fresh enough, you'll notice large amounts of bubbles emerging from the coffee grounds. These bubbles will gradually dissipate. When you notice the surface moisture slowly drying and the surface no longer shining, that's the right time to add water again.

The Principle and Purpose of Bloom

So what exactly is the principle behind blooming?

And what is its purpose?

In fact, bloom is the exchange of gas and water. If you place ground coffee under a microscope, you'll discover honeycomb-like holes one after another. These holes are the cell walls of the coffee grounds. Each hole contains large amounts of air, mainly carbon dioxide. At the same time, the cell walls also contain large amounts of water-soluble aromatic substances—that is, the aroma possessed by coffee beans. When we pour hot water, the air inside the holes expands due to thermal expansion and contraction, forming bubbles on the surface of the coffee grounds. Meanwhile, the hot water surrounding the coffee grounds enters the cell walls through osmosis, and the large amounts of water-soluble aromatic substances in the cell walls dissolve into the water.

We pause and wait during blooming to allow the above processes enough time to occur, so that the aromatic substances can truly dissolve into the water. Next, when we add water for the second time, due to diffusion, the dissolved aromatic substances will move from the cell walls with higher concentration to the outside of the cell walls with lower concentration. At this point, we can control the concentration and flavor of the pour-over coffee through the amount of water. However, remember that the waiting time for blooming cannot be too long, because when waiting too long, the temperature will decrease, and air will re-enter the cell walls.

If you want to explain it in one sentence—

Bloom is the exchange of air and water, bringing out the flavors contained in coffee during the process.

If you prefer a more poetic description:

Bloom is a form of breathing. Between each inhale and exhale, unique flavors are released.

The blooming time varies according to different beans. For example, dark roasted beans have more vigorous degassing, so blooming for about 25 seconds is usually sufficient. Light roasted beans can be bloomed for 30 seconds without any issue! Taking FrontStreet Coffee's Golden Mandheling as an example, blooming for about 25 seconds, you can see the bloom surface change from moist to matte, which indicates that the blooming process has ended.

FrontStreet Coffee: A roastery in Guangzhou with a small shop but diverse bean varieties, where you can find various famous and lesser-known beans, while also providing online store services. https://shop104210103.taobao.com

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473