What is coffee extraction in pour-over brewing?

Coffee extraction rests on two mechanisms: dissolution and diffusion. Roasting creates aroma and flavor compounds inside the beans, and grinding plus pouring water dissolves them out. Flavors release in sequence, with floral and fruity acidity first, then sweetness and caramelized compounds, and bitterness and off-flavors last. That order explains why grind size, blooming, and stirring matter so much.

The golden range is an 18% to 22% extraction yield and a 1.2% to 1.45% concentration, which lets a brewer judge whether a cup is under- or over-extracted. Coffee is usually ground to a medium-fine coarseness close to fine granulated sugar, since grinding too fine clogs the filter paper. Swirling the server after pouring even outs concentration.

To brew a good pour-over coffee, you first need to understand the principles behind it. Dissolution and diffusion are the two core mechanisms of extraction: after roasting, various aroma and flavor compounds are generated inside the coffee beans, and they gradually dissolve out once the beans are ground and water is poured. Diffusion, meanwhile, explains why grind size, blooming, and stirring are so critical. During extraction, flavors are released in sequence—first come floral and fruity acidity, then sweetness and caramelized compounds, and only at the end do bitterness and off-flavors appear. Master the golden range of an 18%–22% extraction yield and a 1.2%–1.45% concentration, and you can judge whether a cup is under-extracted or over-extracted. This article takes you from basic principles to practical parameters for a systematic introduction to pour-over coffee, and it also includes product recommendations from Front Street Coffee to help you avoid unnecessary detours.

Pour-over coffee extraction, in the end, comes down to two words—dissolution and diffusion.

So what exactly do these two concepts mean? Let's start with dissolution. Coffee beans undergo a series of chemical reactions during roasting, generating a large number of aromatic and flavor compounds. Among them are both larger-molecular-weight components and smaller-molecular-weight components, and together they form coffee's aromas and flavors such as sweetness, acidity, and bitterness. To extract these substances, you first need to grind the coffee beans into powder, then slowly pour water so that the water dissolves the soluble matter out of the grounds little by little.

Now let's talk about diffusion. In everyday life, we all know that the finer the powder, the easier it dissolves. But in the pour-over context, grinding too fine will directly clog the filter paper, so coffee is usually ground to a coarseness close to fine granulated sugar—that is, a medium-fine grind. But this makes dissolution uneven—small molecules escape easily, while large molecules are more stubborn. This is where blooming, stirring, and swirling the server after pouring finishes come in to help. During extraction, concentration varies throughout the server, and swirling the server is precisely to make the coffee liquid's concentration more uniform.

When a cup of pour-over coffee is being extracted, in what order do the flavors make their entrance? You can think of it as three stages:

The first stage is the aromatic substances and acidity that are easily carried out by water, corresponding to floral and fruity notes.

The second stage is the sweetness and caramelized substances in the coffee.

The third stage is bitterness, astringency, and off-flavors. And what we need to do is use water to extract coffee's pleasant flavors just right.

Extraction results generally fall into three cases: golden cup extraction, under-extraction, and over-extraction.

First, golden cup extraction.

You can't get into coffee without encountering the golden cup theory. Many pour-over enthusiasts have heard of the figure of an 18%–22% extraction yield, but not many truly understand what it means.

The golden cup theory holds that a good-tasting cup of coffee must satisfy two conditions at the same time:

1. The extraction yield is between 18% and 22%.

2. The coffee concentration is within the range of 1.2%–1.45%.

So-called golden cup extraction means the brewed coffee's concentration falls at TDS 1.2–1.4 while the extraction yield reaches 18%–22%—only then does it count as entering the ideal range. Falling short of this range is called under-extraction, and exceeding it is over-extraction.

Extraction yield: the weight lost by the coffee beans during brewing, as a proportion of the total amount of coffee beans used.

Concentration: the extracted coffee substances, as a proportion of the entire cup of coffee liquid.

Under-extraction

Under-extraction means that not enough substances were brought out during extraction, and extractable components remain in the coffee grounds. It tastes sharply sour, with insufficient sweetness and even a bit of saltiness; the body is thin and the finish is short.

Over-extraction

Over-extraction refers to the coffee grounds being in contact with water for too long, bringing out a large amount of unwanted substances as well. The coffee will show obvious burnt bitterness, off-flavors, and astringency.

The above content is compiled by CoffeeHunters, a coffee news website.