UNDERSTANDING COFFEE EXTRACTION

October 4, 2024 • Drew Horton

Understanding Coffee Extraction: A Beginner's Guide to Taste and Math

If you've spent time around coffee nerds, you've likely heard the term "extraction" thrown around quite a bit. Sometimes it sounds highly technical, but it also seems subjective and can be confusing to pin down exactly what it means. In coffee, "extraction" is simply the process of pulling soluble compounds out of coffee grounds. The way these compounds are extracted—and the flavors they create—are essential to crafting the perfect cup.

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What Is Coffee Extraction?

At its core, coffee extraction refers to what happens when water interacts with coffee grounds. When you brew coffee, the water dissolves various compounds within the beans, which then make their way into your cup. The result is the rich, aromatic liquid we know and love as coffee. However, not all extractions are created equal, and understanding this concept is key to mastering your brew.

Tasting Extraction: How to Identify Under, Over, and Ideal Extraction

Understanding extraction isn’t just about numbers—it’s also about using your senses. Here’s how to identify different levels of extraction by taste:

  • Under-Extracted Coffee: Tastes sour or sharp, lacking sweetness. It may also have a salty note, and the flavors won’t linger on your palate. If your coffee tastes like it disappears too quickly or is overly tart, it’s likely under-extracted.
  • Over-Extracted Coffee: Tastes bitter, astringent, and dry. It might feel rough on the tongue, and the flavors may seem flat or lifeless. If your coffee tastes harsh or leaves an unpleasant aftertaste, it’s likely over-extracted.
  • Ideal Extraction: Tastes sweet, balanced, and complex. The flavors are well-defined and the coffee leaves a pleasant, lingering aftertaste. This is the sign of a well-extracted brew.
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The Math of Extraction: Measuring Strength and Extraction Yield

To know the exact extraction of a coffee involves a bit of math and some fancy equipment, but don’t worry—it’s not as complicated as it sounds. It is not necessary to find the exact extraction of a coffee, but it can help us understand the concept in more detail. Two important concepts in coffee extraction are strength and extraction yield:

  1. Strength refers to the concentration of dissolved solids in your coffee. You can measure it using a refractometer, which tells you how much of your coffee is made up of these dissolved solids. Strength is pretty straight forward; strength will determine the intensity of flavor and is usually dependent on a person's preference.  
  2. Extraction Yield is the percentage of coffee’s weight that’s dissolved into the cup during the brewing process. If you start with 20 grams of coffee and end up extracting 4 grams of dissolved solids into your brew, your extraction yield is 20%. When extraction is discussed, people are usually talking about the extraction yield. Extraction yield will have the most impact on the balance of flavors in the coffee.

Understanding extraction yield helps you predict how your coffee will taste. On average, about 30% of a coffee bean’s weight is soluble, and the optimal extraction yield for a balanced cup generally falls between 18% and 22% as a rough guide.

Flavors Associated with Different Levels of Extraction

Coffee extraction happens in stages, and different compounds in the coffee have different solubility. This means that they are extracted at different points in the coffee:

  • Under-Extraction (Below 18%): When coffee is under-extracted, not enough of the desirable flavors are pulled from the grounds. The result is often a sour, salty, or overly acidic cup. This occurs because the initial compounds dissolved are acids and salts that don’t yet have the balance provided by sugars and other flavors that come later in the extraction process.
  • Over-Extraction (Above 22%): On the flip side, over-extraction happens when too much is pulled from the coffee grounds. This typically results in a bitter, dry, or hollow-tasting brew. The bitterness comes from the later stages of extraction when less pleasant compounds, like tannins, make their way into the cup.
  • Ideal Extraction (18% - 22%): The sweet spot for coffee extraction is usually between 18% and 22%. At this level, you’ll find a balance of sweetness, acidity, and bitterness, creating a well-rounded and flavorful cup. The coffee should have a rich mouthfeel, lingering sweetness, and a pleasant finish.
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The Role of Grinding in Extraction

Grind size has a direct impact on the total brew time and the rate of extraction. A coarser grind cause water to flow more quickly through the coffee bed, reducing the overall brew time. Coarser grinds will also have less surface area and will be dissolved more slowly. A finer grind increases the surface area of the grounds, increasing solubility and slowing down the water flow, increasing the brew time. These factors associated with finer grinds will allow for more extraction, adjusting the grind size is one of the most effective ways to control extraction.

 

It's important to consider that solubility—how easily compounds dissolve—varies between different coffees. Coffees that are heavily processed or grown at lower altitudes tend to be more soluble and will typically need a coarser grind compared to a less soluble coffee. In contrast, high-altitude coffees or those with less processing tend to be denser and less soluble, which means they may need a finer grind or longer brew time to achieve the ideal extraction.

Other Factors Affecting Coffee Extraction

Extraction is influenced by several variables, each of which can be adjusted to dial in your perfect brew. Here's how temperature, coffee-to-water ratio, and brew time play a role:

Temperature

Water temperature is crucial for extraction. Hotter water speeds up the extraction process, drawing out more compounds more quickly. However, this can lead to over-extraction if not managed carefully, resulting in bitterness. Cooler water, on the other hand, slows down extraction, which might leave your coffee tasting under-extracted and sour. The ideal temperature range generally lies around 200°F (93°C), but experimenting slightly above or below this can help you find your preferred balance.

Coffee-to-Water Ratio

The amount of coffee you use compared to water affects both the strength and extraction. A higher coffee-to-water ratio will create a stronger brew, but it may also lead to under-extraction if the other factors aren’t adjusted accordingly. Conversely, using less coffee with more water can dilute the flavors, but may result in over-extraction. Finding the right ratio for your taste is essential—experiment with more or less coffee and notice how it changes the flavor and extraction.

Brew Time

Brew time can indicate how long the water is in contact with the coffee grounds. Longer brew times allow for more extraction, but too long can pull out unwanted bitter compounds. Shorter brew times can result in under-extraction, leading to a sour or weak cup. Adjusting brew time, along with grind size, allows you to fine-tune your extraction to achieve the perfect flavor. However, it is important to note brew time can vary widely based upon the density of the coffee, so it is best to pay attention to brew time relative to other brews of the same coffee.

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Conclusion: Mastering Extraction for Better Coffee

Understanding coffee extraction is one of the most powerful tools in a barista’s arsenal. By mastering the balance between under and over-extraction, you can unlock the full potential of your coffee beans, achieving a cup that’s flavorful, balanced, and deeply satisfying. So next time you brew, pay close attention to the extraction process—you might just discover the secret to your perfect cup.

A Note on High and Low Extractions:

It's important to remember that high or low extraction doesn't automatically mean your coffee is over or under-extracted. The ideal extraction is relative and can vary widely depending on the coffee, brew method, and personal taste. Taste is king—let your palate guide you as you dial in your brew. A well-extracted coffee should amplify the natural flavors of the beans, resulting in a cup that's both focused and transparent.