Alfred Renyi once said that “a mathematician is a machine for turning coffee into theorems,” and while that may or may not be true, we can say with certainty that applying math to coffee brewing unquestionably improved the quality of our cup — namely, the extraction yield percentage. When speaking about coffee, extraction, or everything that is pulled out of the coffee bean as water passes through it, is as essential to creating a delicious cup as bean quality. Extraction yield percent, more commonly referred to as soluble yield (and most commonly thought of as grounds-to-water ratio), is the percentage of coffee that is actually extracted and present in your brewed cup. To understand how extraction yield impacts tastes, we first need to review the coffee bean’s structure.
What is in the coffee bean?
The bean is actually a seed, packed with over 1,000 chemical compounds. While we all know (and love!) caffeine, it is other compounds, primarily lipids (natural fats), acids, sugars, and fibers that create a coffee’s character. The prominence and balance between these other compounds depend on extraction. During brewing, the first compounds to extract are lipids and acids. Lipids are oils that dominate a coffee’s body and acids produce a coffee’s fruit, floral, and citrus tones — essentially very light, gentle flavors. Sugars are extracted next and give coffee natural sweetness and additional body. Plant fibers, which tend to be tart and / or bitter, are extracted last. When balanced extraction is achieved, coffee is pleasingly flavorful and aromatic with clear, balanced acidity and just a touch of bitterness in the base notes to create a round, complete cup. An under-extracted coffee tastes either sour or tart due to the lack of sugars (sweetness) while over-extracted coffee is bitter and off-putting due to an overrepresentation of sugars and plant fibers.
How can I achieve balanced extraction?
Achieving optimal coffee extraction starts by applying the established extraction yield percent and then tweaking the ratios to personal preference. According to the Specialty Coffee Association of America, balanced extraction occurs when the extraction yield is between 18% – 22%. Generally, 18% – 22% extraction yield is achieved with a grounds-to-water ratio of 1 gram coffee to 16 – 18 grams of water. Well, almost achieved. Many additional elements also impact extraction, including water temperature, run-through rate (i.e., brew rate), grind, and brew method. To extract properly, the brew water temperature should be between 195 and 205 degrees Fahrenheit. Temperatures below 195 will not extract upper notes (the acids) and temperatures above 205 will burn the coffee. Brew rate measures the amount of time water remains in contact with the grounds. The longer the grounds are exposed to water, the greater the extraction. Grind and brew method also play an important role in extraction. Each brew method requires a unique grind — largely to account for differences in brew rate. Grounds, in addition to brew rate, control saturation. The smaller the grind, the greater the percentage of the bean is exposed to water, the shorter the brew rate (e.g., espresso). The larger the grind, the longer the brew rate (e.g., a French pressed coffee). Using an incorrect grind will lead to over- or under- extraction.
While experimenting to find your personal preferred extraction yield, we suggest starting with coffee strength and brew method. Immersion brewing methods, such as a French Press, produce oily cups with a heavier mouthfeel than say a drip method. Coffee strength also interacts with extraction. If you enjoy a strong coffee, you likely need to use a higher grounds-to-water ratio. You may, for example, want to start with 1 gram of coffee to 16 or even 15 grams of water and tweak your extraction yield once you’ve found the perfect strength. Bottom line, assuming your beans are fresh and your grind correct, if your coffee tastes sour, it is likely brewing too quickly; if your coffee tastes bitter, it is likely brewing too slowly. We hope this helped clarify what coffee extraction and why achieving balanced extraction is essential to creating a delicious cup. For more on coffee brewing, please visit the following blog entries: