Introduction:Mastering the key elements of coffee extraction, from precisely calculating concentration to extraction yield, is essential for enhancing coffee flavor. This article provides an easy-to-understand introduction to three mainstream methods for measuring concentration, the scientific principles behind extraction yield conversion, and detailed step-by-step instructions and practical formulas for common brewing devices such as immersion, pour over, and espresso. It helps you adjust brewing parameters more scientifically to extract coffee with your desired flavors.
The quality of coffee extraction directly affects the final flavor profile of the coffee, and the key lies in controlling the concentration and extraction yield. About 30% of a coffee bean consists of soluble substances, including aroma, acidity, sweetness, and body. However, not all of these contribute positively to flavor—over-extraction can even amplify undesirable impurities. Therefore, understanding how to properly measure concentration and calculate extraction yield is essential knowledge for any coffee enthusiast looking to advance their skills.
Concentration refers to the proportion of soluble solids in coffee liquid relative to the total liquid volume, usually expressed as a percentage (%) or parts per million (ppm). There are three common methods for measuring concentration on the market: refractometers, conductivity pens, and evaporation drying, each with its own pros and cons and suitable scenarios.
First is the refractometer, often seen as a VST refractometer, which measures the Total Dissolved Solids (TDS) in coffee liquid by detecting changes in the refraction angle of light passing through the liquid. The result is shown as a percentage. It is easy to operate and highly accurate, making it the most commonly used tool among professional baristas. Typically, plain water shows around 0.1%, while well-extracted coffee usually falls between 1.2% and 1.3%.
The conductivity pen, also known as a TDS pen, measures the electrical conductivity of electrolytes in the liquid and converts it to a ppm value. Then, based on the fact that electrolytes make up about 10% of total soluble substances, it estimates the TDS concentration of the coffee liquid, which is then converted to a percentage. While it can also produce similar results, it involves multiple conversion steps and is affected by environmental variables, making it more cumbersome to use.
Evaporation drying is the most traditional and accurate method. It involves evaporating a certain amount of coffee liquid until dry, and the remaining solid weight represents the soluble substances. Dividing this by the original total liquid weight gives the concentration. Although accurate, this method requires laboratory-grade equipment and controlled environments, making it more suitable for research purposes and difficult to perform daily.
Extraction yield refers to the proportion of soluble substances successfully extracted from the total soluble substances in the coffee beans. The calculation formula is generally: “the weight of dissolved substances in the coffee liquid ÷ the weight of total soluble substances in the coffee beans,” expressed as a percentage. According to the “Golden Cup Standard” by the SCAA (Specialty Coffee Association of America) and SCAE (Specialty Coffee Association of Europe), the recommended concentration range is typically between 1.15% and 1.35% or 1.2% and 1.45%, which can be slightly adjusted according to personal taste.
When actually calculating extraction yield, if using a refractometer or conductivity pen, you can multiply the measured TDS value by the total weight of the coffee liquid and then divide by the weight of the coffee beans used. If using the evaporation drying method, you can directly calculate using the weight of the dried solids. It’s important to note that ppm means the number of solute parts per million parts of solution—for example, 1ppm means one part solute in one million parts of solution. This is simply a unit conversion difference from percentage.
For different brewing devices, the calculation of extraction yield is slightly adjusted to better match actual operation scenarios:
For immersion devices such as French press, siphon, or cupping (Cupping), the formula is: “amount of water used × TDS concentration ÷ weight of coffee grounds.” For example, using 240 grams of water, extracting at a concentration of 1.2%, with 15 grams of coffee grounds, the extraction yield would be 19.2%.
For pour over devices such as hand pour, Chemex, AeroPress, or French press (cloth), you can use the formula: “total weight of coffee liquid × TDS concentration ÷ weight of coffee grounds.” If considering coffee grounds absorption, which typically absorbs about twice its own weight in water, the formula can be adjusted to: “(amount of water used − absorbed water) × TDS concentration ÷ weight of coffee grounds.” For instance, using 280 grams of water, assuming the coffee grounds absorb 30 grams, with a concentration of 1.2% and 15 grams of coffee grounds, the extraction yield can reach 20%.
The calculation for espresso machines is slightly different because the extracted liquid is concentrated and contains more suspended fine particles. It is recommended to filter out insoluble particles with filter paper or a specialized filter before measuring TDS to improve accuracy. The formula is: “coffee liquid weight × TDS concentration ÷ weight of coffee grounds.” For example, if the extracted coffee weighs 36 grams, has a concentration of 10%, and uses 18 grams of coffee grounds, the extraction yield is as high as 20%.
Mastering these basic principles and practical formulas allows you to more scientifically adjust factors such as water temperature, grind size, coffee-to-water ratio, and extraction time during daily brewing, further improving the overall flavor performance and consistency of your coffee. Whether you're a beginner in pour over or a fan of espresso, understanding the relationship between concentration and extraction yield is an important cornerstone on the path to specialty coffee.
The above content is compiled by CoffeeHunters, a coffee news website.
