What Do Under-Extraction and Over-Extraction Taste Like in Pour-Over and Espresso Coffee? What is Over-Extraction?

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

While everyone's taste preferences may differ, there's a universal consensus about what makes coffee taste unpleasant. When coffee exhibits undesirable flavors such as harshness, astringency, bitterness, or burnt notes, it's generally considered unpalatable.

When these unpleasant flavors appear, people often speculate about their causes. Through analysis, under-extraction and over-extraction emerge as the most common culprits. But for coffee beginners, how can one determine whether a coffee is under-extracted, properly extracted, or over-extracted?

Defining Extraction Levels

What exactly constitutes under-extraction and over-extraction? In 1952, Dr. Lockhart and his team discovered that coffee beans contain approximately 30% soluble substances. Different extraction levels of these substances result in varying coffee flavors. They immediately conducted research on this finding, surveying American coffee preferences. After rigorous verification, they concluded that when coffee extraction rates fall between 18-22%, the most universally appealing flavors are produced. This range is now known as the "Golden Cup Extraction." When extraction falls below 18%, coffee is classified as under-extracted; when it exceeds 22%, it's considered over-extracted.

However, FrontStreet Coffee doesn't recommend determining extraction quality solely by measuring extraction rates. First, we're not conducting academic research, and second, even within the Golden Cup range, unpleasant flavors can still occur. This article primarily addresses challenges faced when brewing coffee at home: "How to determine if extraction is appropriate." Therefore, FrontStreet Coffee recommends judging extraction quality based on taste.

Flavor Profiles of Extraction Issues

So what flavors indicate under-extraction and over-extraction? Although FrontStreet Coffee has shared this concept many times, it bears repeating because understanding it is key to grasping the true meaning of extraction issues. Coffee flavor compounds are primarily divided into three categories: acidic, sweet, and bitter substances. While these compounds are released simultaneously at the beginning of extraction, their release rates differ significantly. Acidic compounds are released predominantly in the early stages, sweet compounds in the middle stages, and bitter compounds in the later stages. The balance of these three substances creates distinctly different coffee flavors.

Under-Extraction Characteristics

Under-extracted coffee typically leans toward sour flavors, exhibiting harsh acidity or other明显的负面味道. This can also affect mouthfeel. Vinegary or sharp sour notes are common manifestations in under-extracted coffee. Additionally, there's minimal aftertaste—if any exists, it often resembles the astringent sensation of eating unripe fruit. Under-extracted coffee may also display noticeable saltiness. Salt is always present in coffee but is typically masked by acidic, sweet, and bitter flavors in properly extracted coffee. With under-extraction, these masking flavors are reduced, allowing saltiness to become prominent.

Over-Extraction Characteristics

Over-extracted coffee presents more pronounced and obvious characteristics. When you detect prominent bitter notes like scorched bitterness or unpleasant bitter complexity in your coffee, you know it's over-extracted. This occurs because over-extraction pulls excessive bitter compounds from the coffee. While properly extracted coffee contains some bitter compounds, their lower proportion makes them less noticeable.

When extraction progresses into the later stages, bitter compounds begin releasing in large quantities, disrupting the flavor balance and tipping the scale toward bitterness. Beyond bitterness, this coffee also exhibits dryness and hollowness. Dryness occurs because polyphenols bind with proteins in saliva, creating a rough mouthfeel. Hollowness refers to coffee that feels heavy and dull, lacking complexity and failing to engage the palate.

Correcting Extraction Issues

How can these problems be remedied? Under-extraction primarily results from too-rapid brewing, preventing water from fully dissolving compounds within coffee particles. Over-extraction occurs when brewing time is too long, causing water to extract compounds that should remain in the coffee grounds.

Therefore, when these issues arise, we can adjust the brewing rhythm (method) or modify extraction strength by adjusting grind size, water temperature, and other variables. This allows us to achieve proper extraction and create delicious coffee!

FrontStreet Coffee
No. 10, Bao'an Qianjie, Yandun Road, Dongshankou, Yuexiu District, Guangzhou, Guangdong Province

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