What Does Coffee Extraction Tell You About Taste?

Under-extraction and over-extraction are the two main reasons a brewed coffee tastes wrong, and each has distinct signs. Under-extracted coffee tastes weak and watery with sharp sourness, astringency, or saltiness. Over-extracted coffee tastes bitter and dry with woody off-flavors. The fix depends on which problem is present, so identifying the state comes first.

The Golden Cup standard places a reasonable coffee extraction yield between 18% and 22%. Below 18% is under-extraction; above 22% is over-extraction. The range is a reference, not an absolute rule, since bean quality also affects results. A practical adjustment keeps water temperature, time, and water volume fixed and changes only grind size.

When brewing coffee, the reason it tastes bad often comes down to either under-extraction or over-extraction. Front Street Coffee has found that many beginners can tell something is off with their coffee but can't pinpoint the problem. This article starts from the definition of the Golden Cup standard, explaining the reference range of an 18%–22% extraction yield, while also pointing out that the Golden Cup is not an absolute standard and that coffee bean quality also affects the results. It then details the three major signs of under-extraction—weak flavor, watery mouthfeel, and sharp sourness, astringency, and saltiness—as well as the characteristics of over-extraction, such as pronounced bitterness, dryness, and woody off-flavors. Finally, it offers a practical adjustment plan using grind size as the variable while keeping water temperature, time, and water volume fixed, helping everyone quickly find suitable parameters.

Front Street Coffee has noticed that many friends new to pour-over brewing often run into a common problem during practice: the coffee they brew tastes off, but when asked to specify what exactly is wrong, they can't quite put it into words.

In fact, to make a good cup of coffee, simply understanding the basic principles of brewing and keeping extraction parameters within a reasonable range isn't enough—we also need to learn to judge the current extraction state of the coffee.

Because the reason a cup of coffee tastes bad is mostly due to "under-extraction" or "over-extraction" (Front Street Coffee is only discussing the impact at the extraction level here), and these two situations have completely different signs and solutions. Only by first determining which one it is can we treat the root cause and ultimately make a delicious cup of coffee.

So whenever a friend at a Front Street Coffee shop reports that the coffee tastes bad, Front Street Coffee always first asks them to describe exactly what tastes bad, then gives corresponding adjustment suggestions. If you also can't articulate it clearly, no worries—today Front Street Coffee will share how to judge the extraction condition of coffee! What is over-extraction? What is under-extraction? Those who have studied coffee theory should know that the boundary between under-extraction and over-extraction mainly comes from the Golden Cup extraction theory. According to the Golden Cup standard, an extraction yield between 18% and 22% is considered the reasonable range for making coffee taste good; below 18% is under-extraction, and above 22% is over-extraction. But brewing coffee is ultimately an everyday matter—even experienced baristas won't pull out a refractometer to test whether the coffee meets the standard at the drop of a hat, let alone ordinary enthusiasts.

And the most crucial point is that the Golden Cup standard is not absolute truth. Coffee that falls within the Golden Cup range isn't necessarily delicious, and coffee outside the Golden Cup range isn't necessarily bad. Why? This has to do with the quality of the coffee beans themselves. First, we need to know that the soluble substances in coffee beans account for only 30% of the bean's weight. And within that 30%, there are both the desirable flavors we enjoy and some less appealing components. Many times when we find coffee tastes bad, it's because these unappealing substances have the upper hand in the cup.

The proportion of these substances in coffee beans mainly depends on the quality of the beans. The coffee variety, growing environment, and other factors all determine quality. The higher the bean quality, the fewer the unappealing substances, and vice versa. What Front Street Coffee wants to say is, if the coffee beans are of sufficiently high quality, even if we extract most of their soluble substances and the extraction yield exceeds 22%, the coffee won't necessarily taste bad, because it doesn't contain much that's unappealing to begin with. Conversely, if the beans inherently contain a lot of unappealing substances, then even if the extraction yield falls within the Golden Cup range, it won't necessarily taste good.

Of course, this also relates to differences in how substances dissolve. The extraction yield is just an average value—it can't distinguish which substances in the coffee are good and which are bad. So rather than relying on instrument measurements, Front Street Coffee recommends judging the specific extraction situation through the taste characteristics of the coffee based on actual conditions. What are the signs of under-extraction? Based on the above, Front Street Coffee believes everyone has gained some understanding of under-extraction and over-extraction. Under-extraction means only a small amount of flavor substances in the coffee are brought out by the water. For example, if the coffee has 30% soluble substances but only 10% or 15% is dissolved during brewing. Generally speaking, under-extracted coffee will have the following three negative characteristics, or any one of them. Weak flavor: Because many flavor substances haven't had time to dissolve before extraction ends, under-extracted coffee typically has a weak aroma and bland taste.

Very watery: Because the coffee lacks sufficient flavor substances, when the coffee-to-water ratio is relatively small, the concentration will be somewhat lacking. The coffee tastes very watery, with a very thin mouthfeel. Sharp sourness, astringency, and saltiness: Sharp sourness, saltiness, and astringency are all common negative signs in under-extracted coffee. This is because the dissolution rate of coffee flavor substances is affected by molecular weight. Lightweight molecules related to acidity dissolve the fastest and are released in large amounts right from the start; sweet-tasting molecules come next; bitter substances have the largest molecular weight and dissolve the slowest.

Many people stop extraction before the sweet and bitter substances have fully dissolved, so the coffee only contains the acidic substances that dissolved in large amounts at the beginning. Lacking balance from other flavors, the acidity dominates alone, and the coffee may taste extremely sharply sour. You might even taste noticeable saltiness or astringency in under-extracted coffee. When extraction is proper, the saltiness and astringency of coffee are usually masked by other flavors and are generally hard to detect. But when under-extracted, because the other flavors that would mask them are missing, we can taste them in the coffee.

If we taste any or all of the above three negative signs in the coffee, then it's highly likely that the cup is under-extracted. There are many factors that cause under-extraction—for example, grinding too coarse, water temperature too low, time too short, too little water, or even insufficient stirring frequency. As for solutions, since the adjustment approach is the same as for over-extraction, Front Street Coffee will cover them together at the end. What are the signs of over-extraction? Over-extraction is much easier to identify, because over-extraction means extracting too much—dissolving too many of the unappealing things in the coffee, such as large-molecule substances that dissolve more slowly. The signs of over-extracted coffee are mainly pronounced bitterness, dryness, or some muddled flavors like wood and straw. Because we are quite sensitive to these signs, we can often immediately identify over-extraction in coffee.

The cause of over-extraction is the opposite of under-extraction: extraction efficiency is too high. For example, grinding too fine, water temperature too high, time too long, stirring too vigorously, and so on. But in most cases, over-extraction is caused by extraction time being too long. How to improve under-extraction and over-extraction? The causes of over-extraction and under-extraction are simply parameters being too high or too low in efficiency, so we just need to lower extraction efficiency when the coffee is over-extracted and raise extraction efficiency when it's under-extracted. But the difficult part is, with so many parameters affecting extraction, how do we choose what to adjust?

It's actually very simple—we just need to fix a few of the parameters and adjust one specific parameter. Water temperature, grind size, time, and water volume are the four major parameters affecting coffee extraction, and among them only the grind size value is invisible, so we can fix water temperature, time, and water volume, and use grind size as the only variable to adjust. Take Front Street Coffee as an example! Suppose Front Street Coffee is brewing a light-roast coffee bean—then Front Street Coffee would use a water temperature of 91–93°C (86–89°C for dark roast), a 1:15 coffee-to-water ratio, and a two-minute brew time, choosing a commonly used grind setting. If the resulting taste shows signs of under-extraction, grind finer. And if it shows signs of over-extraction, grind coarser.

In this way, we can very quickly find the parameters suited to the current coffee beans, while correcting the coffee's flavor and making it taste good. But this method can only provide preliminary improvement, and besides parameters affecting coffee extraction and flavor, there are many other factors that can have an impact, such as the issue of fines. For these more complex situations, everyone can move on to the "portal" article to learn more—Front Street Coffee won't go into too much detail here. - END -

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