How Do You Calculate Coffee Extraction Yield From TDS?
An ATAGO-style refractometer estimates dissolved solids by measuring how light bends through a coffee sample. Zero the crystal with purified water, stir the brew, draw about 1g, let it cool slightly, then press START for a reading within seconds. The TDS value then feeds into the coffee extraction calculation.
The Golden Cup theory sets two reference ranges: extraction yield of 18% to 22% and concentration of 1.2% to 1.45%. Under-extracted coffee tends toward sourness, while over-extraction brings bitterness. Tracking these numbers gives a repeatable way to judge daily brewing, separate from sensory cues like when coffee smells like alcohol.
Front Street Coffee received a question from an enthusiast who wanted to know how to get started with coffee concentration measuring devices like the ATAGO. This article will demonstrate the device's operating procedure step by step, explain the meanings of the two readings, Brix and TDS, and show how to use the measured TDS value to calculate coffee extraction yield. The article will also introduce the two core criteria of the Golden Cup theory—extraction yield of 18%–22% and concentration of 1.2%–1.45%—as well as the flavor characteristics associated with under-extraction and over-extraction, helping you more accurately judge whether a cup of coffee falls within the ideal range in your daily brewing.
A while ago, a follower asked Front Street Coffee, saying they had a TDS meter but weren't quite sure how to operate it. So today, Front Street Coffee will discuss this topic, covering how to use the device and what problems it can help us solve.
Coffee Concentration Measuring Device
Its working principle is actually based on the phenomenon of light refraction, using changes in the refractive index to estimate the total dissolved solids in a liquid. Looking closely at the instrument panel, you can see two labels: Brix and TDS.
Brix represents the concentration of soluble solids in a sample, and the soluble solids here include all water-soluble components such as sugars, salts, proteins, and acids.
TDS reflects the ratio of soluble substances to water in a cup of coffee. The higher the TDS value, the more substances are dissolved per unit of water.
After briefly explaining the principle of the concentration measuring device, Front Street Coffee will now demonstrate the operating steps: 1. Press the "START" button to wake up the device, first drip a little purified water onto the surface of the refracting crystal, then press "ZERO" to complete the zero calibration;
2. Stir the freshly brewed coffee evenly, immediately draw about 1g of sample and let it sit for about one minute, wait for the temperature to drop a bit before dripping it onto the refracting crystal, press "START" to begin measurement, and the reading will appear within a few seconds.
After measuring, don't forget to wipe the crystal area clean with water or alcohol. So what's the use of these numbers once you have them? With these parameters, we can further calculate the extraction yield of the coffee.
Extraction Yield: refers to the weight lost from coffee beans during brewing as a proportion of the total amount of coffee beans used. To put it plainly, it's how much of the original coffee grounds was actually carried away by the water.
For example, if you used 100g of coffee grounds to brew, and after brewing you completely remove the moisture from the spent grounds (by oven-drying or sun-drying, either works), and if 80g remains, that means 20g of substances entered the coffee liquid, so the extraction yield of this cup is 20%. In the coffee community, there is a concept called: the Golden Cup theory!
In actual brewing, in order to balance the coffee's original flavors while avoiding unpleasant off-flavors, the balanced ratios in between have formed several widely recognized standards, commonly known as the Golden Cup theory. The Golden Cup theory proposes that "delicious coffee" needs to simultaneously meet the following two conditions:
1. Extraction yield falls between 18% and 22%
2. Coffee concentration is within the range of 1.2%–1.45%
Calculation formula: (coffee liquid weight * TDS%) / powder weight = extraction yield
When the extraction yield is below 18%, the coffee tends to taste sour, with a thin body, bland flavor, and lack of complexity; when the extraction yield exceeds 22%, problems such as increased bitterness, hollow flavor, and noticeable astringency gradually appear. Take drip coffee for example, a coffee-to-water ratio roughly between 1:15 and 1:22 can be broadly classified as within the Golden Cup range, but that doesn't mean falling within this ratio equals the Golden Cup. Also note that the coffee-to-water ratio is not the same as the coffee-to-liquid ratio, and even less does it represent concentration. However, conversely, a standard Golden Cup coffee-to-water ratio will basically fall within the above range.
The above content is compiled by CoffeeHunters, a coffee news website.
