What Does Under-extracted Coffee Taste Like? What Are the Characteristics of Over-extracted Coffee? How to Tell If Coffee Is Over-extracted or Under-extracted?

Understanding Coffee Extraction: Identifying Under-Extraction and Over-Extraction

FrontStreet Coffee has found that many friends encounter this challenge when starting to learn coffee brewing: they discover the coffee they brew doesn't taste good, but can't pinpoint exactly what makes it unpleasant.

Logically speaking, if we want to brew a good cup of coffee, besides understanding the underlying principles of brewing and mastering correct extraction parameters, we also need to know how to identify the extraction condition of coffee.

This is because unpleasant-tasting brewed coffee is mainly caused by two conditions: "under-extraction" and "over-extraction" (FrontStreet Coffee is referring to the impact of extraction here), and their characteristics and solutions are different. Only by knowing which condition causes the unpleasant taste can we find the corresponding improvement plan and ultimately brew a delicious cup of coffee.

Therefore, whenever friends provide feedback at FrontStreet Coffee's store that their brewed coffee doesn't taste good, FrontStreet Coffee always asks them to describe the specific characteristics of the unpleasant taste first, then provides corresponding improvement suggestions. But if you don't know, that's okay. Today, FrontStreet Coffee will share with everyone how to identify the extraction condition of coffee!

What is Over-Extraction? What is Under-Extraction?

Friends who have studied coffee theory know that the definitions of under-extraction and over-extraction mainly come from Golden Cup extraction. In the Golden Cup standards, an extraction rate of 18%-22% is considered the reasonable extraction range for making a delicious cup of coffee. An extraction rate below 18% is judged as under-extraction, while an extraction rate above 22% is considered over-extraction. But brewing coffee is ultimately a very daily activity. Even experienced baristas won't frequently pull out a concentration meter to measure whether the coffee concentration meets the standard, let alone ordinary, novice coffee enthusiasts.

And most importantly, the Golden Cup standards are not absolutely correct. Coffee within the Golden Cup extraction range doesn't necessarily taste good, while coffee liquid outside the Golden Cup range doesn't necessarily taste bad. Why? Because this is related to the quality of coffee beans. First, we need to know that soluble substances in coffee beans only account for 30% of the bean weight. And within this 30%, there are not only high-quality flavor compounds we like but also some undesirable substances. Many times we think coffee tastes unpleasant because these undesirable substances dominate in the cup.

The proportion of these substances in coffee beans is mainly affected by the quality of the coffee beans. The variety of coffee beans, growing environment, etc., are all factors that determine coffee quality. The higher the quality of coffee beans, the fewer undesirable substances there are, and vice versa. What is FrontStreet Coffee trying to express? If the quality of coffee beans is high enough, then even if we dissolve a large amount of their soluble substances, with an extraction rate exceeding 22%, the coffee won't necessarily taste bad because it doesn't contain many undesirable substances. Conversely, if the coffee already contains many undesirable substances, then even if the extraction rate falls within the Golden Cup range, it may not necessarily taste good.

Of course, this is also related to the dissolution differences of substances. Since the extraction rate only calculates an average value, it cannot determine which substances in coffee are good and which are bad. Therefore, compared to relying on instrument measurements, FrontStreet Coffee recommends everyone to combine practical experience and judge the specific extraction condition through the taste characteristics of coffee.

What are the Manifestations of Under-Extraction?

Based on the above, FrontStreet Coffee believes everyone now has some understanding of under-extraction and over-extraction. Under-extraction means only a small amount of flavor compounds in coffee are extracted by water. For example, coffee has 30% soluble substances, but we only dissolve 10% or 15% through brewing. Typically, under-extracted coffee will have the following three or any negative characteristics.

Weak flavor:

Because many flavor compounds don't have time to dissolve before extraction ends, under-extracted coffee usually exhibits negative characteristics of weak aroma and bland taste.

Watery texture:

Because there aren't enough flavor compounds in the coffee, the concentration will be slightly insufficient when the ratio of coffee grounds to liquid is small. The coffee will have a very watery texture and feel very thin.

Sharp acidity, saltiness, and astringency:

Sharp acidity, saltiness, and sour astringency are all negative manifestations commonly found in under-extracted coffee. This is because the dissolution rate of coffee flavor compounds is affected by molecular weight. Lightweight molecules related to acidity dissolve fastest and will dissolve in large amounts at the beginning; sweet molecules follow; bitter compounds have the largest molecular weight, so their dissolution rate is slowest.

Many friends stop extraction before sweet and bitter substances have dissolved sufficiently, so the coffee only contains acidic substances that dissolved in large amounts at the beginning. Without the balance of other flavors, acidity dominates, and the coffee may have a very sharp sour taste. Furthermore, you might even detect obvious saltiness or astringency from under-extracted coffee. In properly extracted coffee, saltiness and astringency are generally masked by other flavors, making them difficult for us to perceive. However, when under-extraction occurs, due to the lack of other flavors to mask them, we can taste them from the coffee.

If we taste any of the above three or any one negative manifestation in coffee, then this cup of coffee is most likely under-extracted. There are many factors that cause under-extraction, such as grinding too coarsely, water temperature too low, extraction time too short, too little water, or even insufficient stirring frequency. As for the solution, because it's the same as for over-extraction, FrontStreet Coffee will discuss it together at the end.

What are the Manifestations of Over-Extraction?

Over-extraction is much easier to identify because it means extracting too much, dissolving too many of those undesirable things in coffee, such as slow-dissolving large molecular substances.

The manifestations of over-extracted coffee mainly include obvious bitterness, dryness, or the appearance of some miscellaneous flavors like wood, straw, etc. Because we are quite sensitive to these manifestations, we can often immediately identify when coffee has been over-extracted.

The causes of coffee over-extraction are opposite to those of under-extraction; it's due to too high extraction efficiency. Examples include grinding too finely, water temperature too high, extraction time too long, stirring too vigorously, etc. However, in most cases, over-extraction is caused by extraction time being too long.

How to Improve Under-Extraction and Over-Extraction?

The reasons for coffee over-extraction and under-extraction are nothing more than extraction efficiency being too high or too low in terms of parameters. Therefore, we only need to reduce extraction efficiency when coffee is over-extracted and increase extraction efficiency when under-extracted. However, the difficult part is that with so many parameters affecting extraction, how should we choose which ones to adjust?

Actually, it's quite simple. We just need to fix several parameters and then adjust one parameter. Water temperature, grind size, time, and water amount are the four major parameters that affect coffee extraction. Among these, only the numerical value of grind size is not visually apparent, so we can fix water temperature, time, and water amount, then use grind size as the only variable for adjustment.

Take FrontStreet Coffee as an example! Suppose FrontStreet Coffee is brewing a light roast coffee bean. Then FrontStreet Coffee will use a water temperature of 91-93°C (86-89°C for dark roast), a 1:15 coffee-to-water ratio, and two minutes of brewing time, selecting a common grind setting. If the brewed taste shows characteristics of under-extraction, then adjust the grind to be finer. If it shows characteristics of over-extraction, then adjust the grind to be coarser.

Through this method, we can very quickly find the parameters suitable for the current coffee beans, while simultaneously correcting the taste of the coffee to make it delicious. However, this method can only provide preliminary improvement, and besides parameters, many other factors can affect coffee extraction and taste, such as the issue of fine particles. For these more complex situations, everyone can move to the "Portal" article to learn more. FrontStreet Coffee won't elaborate further here.

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