How to Distinguish Under-Extraction and Over-Extraction in Coffee? What Are the Signs of Over-Extracted Coffee? Why Does Coffee Lack Aftertaste?

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

Whether for espresso or pour-over, learning to judge the extraction level of coffee is absolutely essential for making a delicious cup. Only when you know what's good and what's not good about a cup of coffee can you apply corresponding corrections to create even more delicious coffee.

Although everyone's definition of good taste may vary, there is consensus on what tastes bad! Therefore, once coffee extraction has problems, these issues will manifest in the flavor, creating "defects." We only need to capture these defects to understand what problems exist in the coffee's extraction, and then make adjustments accordingly.

Right! Let's first establish a premise: although the Golden Cup standard defines under-extraction and over-extraction, we should preferably not judge extraction levels by numerical values. Because coffee can vary in bean quality and processing methods, the Golden Cup extraction theory may not always be accurate. Coffee within the Golden Cup extraction range isn't necessarily delicious, and coffee outside this range isn't necessarily unpleasant. Therefore, we should return to the essence of coffee, using the actual tasting experience as the basis for judgment.

Now, without further ado, FrontStreet Coffee will discuss what characteristics under-extracted coffee might exhibit!

Under-extraction

Under-extraction means hot water hasn't fully extracted the coffee, resulting in insufficient content in the final brew, leading to the following characteristics:

Prominent, sharp acidity: Sour, sweet, bitter, and salty are the four flavors we can extract from coffee. Since these four flavors are mutually opposing and constraining, they are all indispensable in a cup of coffee. We can think of coffee like lemon tea – a delicious lemon tea needs not only the acidity of lemon but also the sweetness of fructose, as only with added fructose can the high acidity of lemon be softened, making the entire lemon tea acceptable to most people.

In yesterday's article, FrontStreet Coffee mentioned that these four flavors have different dissolution rates due to their different molecular sizes, so they require complete extraction to achieve a balance where each flavor has sufficient quantity to counterbalance the others. When we under-extract, the coffee will be filled with excessive acidity because it has the fastest dissolution rate. Without the balance of other flavors, acidity becomes particularly prominent, sharp, and uncomfortable. Conversely, lacking sweetness or the rich mouthfeel that bitterness brings is also a sign of under-extraction.

Saltiness appears and becomes noticeable: Unlike umami, although saltiness has a weak presence in coffee, it is indeed an existing flavor. It just has a low proportion in coffee, making it difficult to detect under the cover of other flavors. When under-extracted, lacking the mask of many other flavors, saltiness will reveal itself. Or rather, it becomes more easily perceived by people, so the appearance of saltiness in coffee is also a sign of under-extraction.

Insufficient or no aftertaste: Aftertaste, sweet aftertaste, and other sensations that appear after drinking coffee are phenomena caused by the dissolution of coffee substances remaining in the mouth. When we under-extract, the aromatic substances in the coffee are significantly reduced, so the aftertaste won't be as obvious or prominent. In some cases, there may be virtually no aftertaste at all.

Weak and flat flavor: Under-extraction, simply put, means insufficient extraction – failing to fully extract substances from the coffee, including flavor compounds! Many flavor compounds require different substances to work together, again similar to lemon tea. When under-extracted, a flavor might lack many of its necessary components, and the isolated taste cannot provide a satisfying experience. Therefore, indistinct and thin flavors are also signs of under-extraction.

Over-extraction

Over-extraction is the opposite extreme of under-extraction. If under-extraction means extracting too little, over-extraction means extracting too much – extracting things that shouldn't be extracted! Ultimately, the coffee will exhibit these characteristics:

Bitter! Extremely bitter: When we over-extract from coffee grounds, the proportion of bitterness easily increases significantly. Because humans are more sensitive to bitterness, when the proportion of bitterness in coffee is too high, it greatly suppresses the expression of other flavors, making the entire cup of coffee seem overwhelmingly bitter!

Hollow, monotonous mouthfeel: Although bitter substances can enhance the richness of coffee, this is only true under appropriate conditions. When there are too many bitter substances, the effect reverses – not only does the richness not manifest well, but the overflow of bitterness reduces the expression of other flavors, making the overall coffee feel hollow, lacking depth, and quite monotonous.

Unpleasant flavors and astringency emerge: The overflow of bitterness isn't the only manifestation of over-extraction. Often, people want to avoid over-extraction for another reason: the release of unpleasant flavors and astringency. Although coffee beans contain 30% soluble substances, not all of them are positive! This includes unpleasant substances like off-flavors and astringency. When coffee is over-extracted, these unpleasant flavors and astringent sensations will emerge one after another, combining with bitterness to create an unpalatable taste.

In summary, whenever we experience these corresponding negative situations in coffee tasting, it indicates that the coffee extraction has problems! Of course, some coffee extractions might not meet all conditions in one direction. For example, channeling in espresso – because of uneven water distribution through the coffee puck – can cause a single shot to exhibit both under-extracted and over-extracted flavors simultaneously. This is uneven extraction.

When coffee extraction shows negative characteristics, we need to make certain adjustments for the next extraction – either increasing or decreasing extraction. The principle is the same for both espresso and pour-over! After all, although they are different extraction methods, theoretically they are the same! As the saying goes, different professions are like different mountains, but it's important to know that different professions don't mean different principles.

- END -

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473