Essential Guide for Coffee Beginners: Understanding Bitterness and Over-Extraction in Pour-Over Brewing

Many friends just starting out run into the frustration of over-extraction. What we call "over-extraction" simply means extracting too much. In a coffee bean, the substances that water can dissolve make up about 30% of the total. Even though that is all there is to work with, we cannot extract everything.

That is because, alongside the pleasant substances that bring us joy, there are also undesirable ones that give coffee negative traits such as bitterness, astringency, and off-flavors. When these are extracted in large quantities, the whole cup becomes unpalatable, and when that happens we call it over-extraction.

If we want to avoid drinking an unbearably bitter, off-flavor-filled over-extracted coffee, it's best to find the right extraction parameters and control the extraction rate properly. (Under-extraction can also cause astringency, bitterness, and off-flavors, but less prominently.) Of all the parameters, grind size, water temperature, and time are the three key factors affecting extraction. So today FrontStreet Coffee will share how to adjust and correct these parameters when the coffee we brew comes out over-extracted.

Coffee Grind Size

First we should question the grind size, because many novice brewers cause over-extraction through grind issues. Grind size lacks the intuitive numeric value of other parameters, so most of the time we can only judge it roughly by eye, which easily leads to over-extraction through misjudgment. (Guess which of the two coffee powders below is coarser.)

(Answer: the right one is coarser. The left has an 85% pass rate through a #20 sieve, while the right has 75%.) Take the image above as an example. When grinding light roast coffee, we want a fineness similar to fine sugar particles, with a 75% pass rate through a #20 sieve, but the current setting produces powder with an 85% pass rate. By eye alone we can hardly tell that this powder is finer than the setting; we just think it looks about right and start brewing. Since the particles are finer and present more surface area to the water, the dissolution rate increases. With other parameters unchanged, the coffee then extracts more than we intended, raising the odds of over-extraction.

So if we brew to a specific recipe but find the final coffee very bitter and full of off-flavors, we can first make the grind coarser. Coarsening the particles reduces extraction efficiency and guards against over-extraction. After all, the other parameters are visual: when their values differ from the recipe, we can spot and correct them directly. If you want to know roughly what your current setting grinds to, FrontStreet Coffee recommends buying a #20 sieve online, which gives a general range. The 75% pass rate through a #20 sieve that FrontStreet Coffee often mentions means that 75% of the ground powder passes through the sieve.

Keep in mind, though, that pass rate offers only a rough reference. If 75% passes through, how fine is that 75%? Is it uniform? How much extremely fine powder is there? Those are things it cannot determine. (Related article: How to use a #20 sieve.) Beyond grinding too fine, another grind problem can invite over-extraction: poor grind quality that produces too many extremely fine particles.

When the grinder isn't good enough, the grind is not only very uneven but also heavy with fine particles. FrontStreet Coffee often notes that a moderate amount of fines helps build complexity, but once there are too many, coffee easily over-extracts, because substances in fine particles dissolve more easily, including bitter compounds. And because fines are extremely small, they can clog the filter paper during brewing, extending extraction time and causing the normally sized particles to over-extract as well.

In such cases, FrontStreet Coffee recommends using a flour sifter to remove some of the fines before brewing. For the specifics, you can refer to FrontStreet Coffee's earlier articles, so we won't go further here.

Extraction Time

Next is extraction time, meaning how long water stays in contact with the coffee powder to dissolve substances. A longer extraction time dissolves relatively more substances, so a longer time makes over-extraction more likely. What counts as long isn't standardized, though, because whether the time is 2 minutes, 3 minutes, or 4 minutes, we can still brew a delicious pot. It depends on whether the time and the other parameters combine appropriately, much like in "What Water Temperature Makes the Best Tasting Coffee?" that FrontStreet Coffee recently shared.

Using the same example, when FrontStreet Coffee brews a 15g pot of light roast coffee, the parameters are: water temperature 92°C, coffee-to-water ratio 1:15, grind size with a 75% pass rate through a #20 sieve, combined with three-stage pouring. Under these parameters, 2 to 2.5 minutes is the optimal extraction time. If the time reaches 3 or 4 minutes, then for these parameters it is too long, and the brew is highly likely to pull out all the negative bitterness, off-flavors, and astringency. If the time really does reach 3-4 minutes, we need to reduce the extraction time to cut down the dissolved negative substances. Many factors affect time, including the fine-particle clogging FrontStreet Coffee mentioned earlier. Another is the dripper: the size of the drainage hole, the number of flow ribs, and how far they protrude all directly affect drainage speed. To shorten extraction time and speed up drainage, consider a fast-flow dripper like the V60, which has prominent ribs and a large drainage hole.

Time is also controlled by pouring speed. Without forming clogs, a faster pour drains faster and shortens extraction time, and vice versa. So if we want to shorten extraction time, increasing pouring speed is another good method. (Put simply, increase the water flow to pour more hot water in the same amount of time.)

Water Temperature

Finally, water temperature. It determines the rate at which substances dissolve, but since FrontStreet Coffee has covered this in detail in "What Water Temperature Makes the Best Tasting Coffee?" we won't go too deep here. In fact, water temperature is the easiest to determine. Generally, when the other parameters aren't too extreme, water temperature falls in the 86-93°C range. With the same parameters as above and everything else unchanged, FrontStreet Coffee controls water temperature between 86-88°C when brewing dark roast coffee, and between 90-93°C when brewing medium-light to light roast coffee. When the brewed coffee tastes too bitter, we can reduce extraction efficiency by lowering the water temperature slightly.

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FrontStreet Coffee Recommendation

A forgiving bean makes it much easier to stay inside the sweet spot, and FrontStreet Coffee's Yirgacheffe Guodingding is a great place to start. Washed in the most traditional style at a cooperative in the Worka area, it shows bright citrus and lemon acidity with jasmine fragrance and a green-tea sweetness, and its acidity is soft and bright rather than sharp, so small slips in brew parameters rarely ruin the cup.

If you prefer a fuller, lower-acid profile, FrontStreet Coffee's Brazil Queen Estate coffee is balanced and gentle, with rich nut and cocoa aromas and clear caramel sweetness. It goes down smooth without astringency and works for pour-over, espresso, and the moka pot, making it a dependable benchmark for an everyday cup.