The Science of Coffee Extraction: What's Really Happening in Your Cup

When talking about specialty coffee, we often hear words like acidity, sweetness, bitterness, or balance. However, behind these sensations we perceive in the mouth lies a much more fundamental phenomenon called extraction. It is extraction that determines whether a coffee will be vibrant, complex, and sweet, or, conversely, flat, aggressive, or unbalanced.

Extraction is simply the process by which water dissolves the compounds contained in ground coffee. Each coffee bean is composed of hundreds of different substances, and each of them contributes to the final cup. Some bring acidity and liveliness, others sweetness and body, while some, heavier ones, create bitterness and a drier sensation in the mouth. What's fascinating is that these compounds do not all extract at the same rate. The easiest to dissolve come first, then sugars and more complex elements, and finally the most bitter compounds.

This is why extraction is not simply a matter of "more or less," but rather a matter of balance. A good coffee is not one from which the maximum possible matter is extracted, but one from which the right proportion of each component is extracted.

When this balance is not achieved, we speak of underextraction. In this case, the water has not managed to extract enough compounds from the ground coffee. In the cup, this often results in an overly sharp, sometimes aggressive acidity, a lack of sweetness, vegetal notes, and a short finish. It's a coffee that feels incomplete, as if something is missing. The causes are usually quite simple: a grind that is too coarse, an infusion time that is too short, water that is too cold, or a flow rate that is too fast, preventing the water from interacting sufficiently with the coffee.

Conversely, we find overextraction. Here, the water has gone too far in the process and has begun to extract compounds that are not desired in large quantities. The result is often dominant bitterness, a dry sensation in the mouth, and a loss of aromatic clarity. The coffee becomes tiring to drink, even if it may seem very intense. This usually happens with a grind that is too fine, an extraction that is too long, a temperature that is too high, or a flow that is too slow.

A very common confusion in the coffee world is to mix the strength of a coffee with its extraction level. However, these are two completely different concepts. Strength corresponds to the concentration of coffee in the cup, in other words, how "loaded" the beverage is. Extraction, on the other hand, corresponds to the amount of material removed from the ground coffee. A coffee can therefore be very strong while being perfectly extracted, or conversely, weak but poorly extracted. This distinction is essential to understand why a coffee can seem intense without being unbalanced.

For a long time, the coffee industry used a reference zone of eighteen to twenty-two percent extraction as an ideal benchmark. This idea comes from the famous Coffee Brewing Control Chart, developed decades ago. Today, modern research in coffee science, particularly from the UC Davis Coffee Center and work used in training like Barista Hustle's Advanced Coffee Making, shows that this range is not an absolute rule. Some coffees can be exceptional below this threshold, while others shine beyond it. This zone remains useful as a starting point, but it does not solely define the quality of a cup.

To delve even deeper into understanding, professionals sometimes use a tool called a refractometer. This device measures the amount of dissolved solids in the beverage, known as TDS. From this value, it becomes possible to calculate the extraction yield and precisely understand what is happening in the cup. This moves from simple taste perception to measurable and reproducible analysis, which is particularly useful for baristas and roasters.

What makes extraction even more complex is that it constantly varies depending on several factors. Grind size, brewing method, water turbulence, coffee solubility related to roasting, and even particle distribution all play a role. This is why two coffees prepared with the same recipe can sometimes yield very different results.

Ultimately, understanding extraction means understanding the very heart of specialty coffee. It's not just a matter of technique, but also a more subtle reading of what's happening in the cup. When a coffee is too acidic or too bitter, the problem doesn't always come from the bean itself, but often from how its compounds were extracted. And that's precisely where the magic of coffee begins to reveal itself.

Sources

Barista Hustle. (n.d.). Advanced Coffee Making (ACM) and coffee extraction resources.
Retrieved from: https://www.baristahustle.com

UC Davis Coffee Center. (n.d.). Coffee Research and Extraction Science.
University of California, Davis.

Specialty Coffee Association. (n.d.). Brewing Standards and Coffee Brewing Control Chart.
https://sca.coffee

Lockhart, E. E. (1957). The Coffee Brewing Control Chart.
Technical publication serving as the basis for modern extraction standards.

VST. (n.d.). TDS Measurement and Coffee Refractometry Research.
https://www.vstapps.com