Introduction:Want to precisely control the extraction quality of your pour over coffee? This article provides a detailed walkthrough of how to operate the ATAGO coffee concentration meter, explains the difference between Brix and TDS, and teaches you how to calculate extraction yield based on TDS values. It also delves into the key criteria of the Golden Cup Theory—extraction yield of 18%–22% and concentration of 1.2%–1.45%—to help you determine whether your coffee falls within the ideal flavor range, avoiding common issues like under-extraction or over-extraction.
Many coffee enthusiasts aim to master more scientific brewing parameters during extraction, among which TDS (Total Dissolved Solids) concentration is a key indicator. Professional coffee concentration meters like those from ATAGO are tools that help us measure these values. This article will start from scratch, guiding you through its basic principles, operation methods, and further teaching you how to use the measured TDS value to estimate the coffee’s extraction yield.
The core operating principle of this instrument is based on the phenomenon of light refraction. When light passes through a liquid, its refractive index changes with the concentration of dissolved solids in the liquid. The instrument detects this change to estimate the total amount of soluble substances in the liquid. Looking at the instrument panel, you can usually see two main displayed values: Brix and TDS.
Brix generally represents the concentration of soluble solids in the sample, including all water-soluble substances such as sugars, salts, proteins, and acids. TDS, on the other hand, directly reflects the ratio of dissolved substances to water in the coffee liquid. The higher the value, the more extracted material is present per unit of water, usually indicating a richer and more intense taste.
Next, let’s go over the actual operation process. First, press the “START” button on the instrument to power it on. Then, place a small drop of pure water on the surface of the refractometer prism and press the “ZERO” button to calibrate it to zero. This step ensures the accuracy of the measurement starting point. After calibration, it is recommended to thoroughly stir the freshly brewed coffee liquid, then immediately draw about 1 gram of the coffee sample, let it sit for about a minute to slightly cool down, and then place the sample on the prism. Press “START” to begin the measurement. After a few seconds, the TDS value will be displayed on the screen. After use, remember to gently wipe the prism area with clean water or alcohol to maintain the instrument’s cleanliness and accuracy.
So, how do these values help with actual brewing? The answer is that through the TDS value, we can further calculate the coffee’s “extraction yield.” Extraction yield refers to the proportion of coffee bean material that is dissolved into the coffee liquid during the brewing process. For example, if you use 100 grams of coffee grounds for brewing, and after removing all moisture from the spent grounds there are 80 grams left, it means 20 grams of material have entered the coffee liquid—that is, the extraction yield of that cup of coffee is 20%.
In the coffee industry, there is a widely recognized “Golden Cup Theory (Gold Cup Theory)” that serves as the standard for evaluating whether a cup of coffee achieves an ideal flavor profile. According to this theory, a “good-tasting coffee” must meet two main criteria: first, the extraction yield should fall between 18% and 22%, and second, the concentration of the coffee liquid (i.e., the TDS value) should be within the range of 1.2% to 1.45%. A commonly used formula for calculating extraction yield is: (Coffee liquid weight × TDS%) ÷ Coffee grounds weight = Extraction yield.
If the extraction yield is below 18%, the coffee often tastes overly acidic, thin, and lacks complexity, with insufficient flavor development. Conversely, if the extraction yield exceeds 22%, it tends to result in noticeable bitterness, astringency, and an empty or hollow flavor. Therefore, maintaining the extraction yield within this golden range is one of the keys to brewing delicious coffee.
Additionally, many pour over coffee enthusiasts often hear about the recommended coffee-to-water ratio, typically between 1:15 and 1:22. This range does indeed broadly align with the extraction zone of the Golden Cup Theory. But note that the coffee-to-water ratio is not directly equivalent to concentration, nor is it the same as the coffee-to-liquid ratio—it is just one of many factors that influence the final extraction outcome. To truly meet the Golden Cup standards, in addition to controlling the coffee-to-water ratio, you also need to pay attention to grind size, water temperature, brewing time, and technique.
In summary, using the ATAGO concentration meter not only helps you accurately monitor the TDS value of each cup of coffee, but also allows you to further calculate the extraction yield and determine whether it meets the Golden Cup Theory standards. With these scientific data points, you can adjust your brewing parameters with more confidence, avoid common issues like under-extraction or over-extraction, and brew coffee with balanced flavor and rich layers.
The above content is compiled by CoffeeHunters, a coffee news website.
