Introduction:Extraction is the soul of pour over coffee. How can you adjust grind size and coffee-to-water ratio to bring out the ideal flavors? This article delves into the causes of over-extraction and under-extraction, explores how grind fineness, water temperature, and pouring techniques affect the final taste, and provides practical parameter suggestions to help you accurately master the optimal extraction conditions for each coffee bean.
Behind an outstanding pour over coffee lies the key to precisely controlling the degree of extraction. Coffee beans contain about 30% soluble flavor substances, yet only 18% to 22% of these are the desirable acidic and sweet components—the rest may introduce unpleasant off-flavors or excessive bitterness. Over-extraction often results in bitterness overpowering acidity and sweetness, throwing off the balance of the overall taste; under-extraction tends to make the coffee taste thin, watery, and lacking in complexity. What exactly determines these extraction outcomes? We will analyze grind size, water temperature, and pouring methods one by one to help you adjust to the most suitable brewing strategy.
Extraction, in essence, is the process of using hot water to dissolve and release flavor compounds from coffee grounds. About 70% of a coffee bean consists of woody fiber, while only 30% contains substances capable of releasing flavor. Notably, within this 30%, around 20% are positive components that contribute desirable acidity and sweetness, while the other 10% may produce undesirable bitterness. Therefore, we do not need to extract all soluble substances—keeping the extraction rate between 18% and 22% allows us to achieve a balanced and pleasant taste.
When we talk about over-extraction, it usually refers to the coffee grounds being in contact with hot water for too long, causing excessive negative flavor compounds to be released, resulting in a cup where bitterness dominates and acidity and sweetness are masked. There are two common causes for this: one is grinding too finely, which allows water to penetrate more easily and extends the extraction time; the other is using water that’s too hot, accelerating the speed of flavor release. Additionally, even if the grind size and water temperature are set appropriately, using a slow water flow during pouring can prolong the time it takes for water to pass through the coffee bed, also potentially leading to over-extraction.
Different roast levels of coffee beans have distinctly different internal structures, which directly affect the most suitable grind size and water temperature settings. Generally speaking, beans roasted at light to medium or medium roast levels have a tighter structure, so it is recommended to use a medium-fine grind—particle size similar to fine sugar (approximately 75–80% passing through China's No. 20 standard sieve)—with water temperature controlled between 90–91°C. This helps extract flavors moderately without over-extracting. For medium-dark to dark roast beans, whose structure is looser, it is advised to switch to a medium-coarse grind—particles resembling coarse sugar (approximately 65–70% passing through China's No. 20 standard sieve)—and lower the water temperature to 88–89°C to avoid over-extraction that could lead to bitterness and astringency.
On the other hand, under-extraction refers to coffee grounds having too short a contact time with water, such that most of the flavor compounds that should have been extracted remain unreleased, resulting in a thin, lackluster cup that may even exhibit unbalanced bitterness. This issue often arises when the grind is too coarse or the water temperature is too low. If these basic parameters are correct but the coffee still tastes noticeably watery, it might be due to using too fast a water flow during pouring, causing the water to rush through the coffee bed or even bypass it along the edges of the filter, thereby diluting the coffee liquid that should have been extracted and further weakening flavor expression.
Overall, adjusting the flavor of pour over coffee requires simultaneous consideration of grind size, water temperature, and pouring technique. Beginners are advised to start with a medium-fine grind and 90°C water temperature, paired with moderate pouring speed and an evenly distributed coffee bed, then gradually fine-tune to find their ideal extraction balance. Observing changes in coffee extraction color, flow rate, and aroma release are also important indicators for determining whether the desired extraction has been achieved.
The above content is compiled by CoffeeHunters, a coffee news website.
