What is total dissolved solids (TDS) in coffee?

At its core, TDS is a scientific metric that translates the 'strength' of your coffee into a precise number. When you brew coffee, hot water acts as a solvent, pulling soluble compounds—such as sugars, acids, and oils—out of the ground beans. TDS measures the percentage of the final liquid that consists of these dissolved solids, with the remainder being water. For example, a filter coffee with a 1.3% TDS means that 1.3% of the cup is coffee material, while 98.7% is water.

To measure this, professionals and home enthusiasts use a refractometer. This device measures the refraction of light as it passes through a sample of your brew; because dissolved coffee solids change the way light bends, the device can calculate the concentration with high accuracy. While a refractometer provides the TDS percentage, it is important to distinguish this from extraction yield. TDS tells you how concentrated the cup is, but extraction yield tells you what percentage of the original dry coffee grounds ended up in your cup.

Understanding these numbers allows you to move beyond guesswork. By combining your TDS reading with your brew ratio—the amount of dry coffee used versus the final liquid yield—you can calculate your extraction percentage. The industry standard for a balanced filter coffee typically falls between 18% and 22% extraction yield, with a TDS range of 1.15% to 1.45%. Espresso, being much more concentrated, typically ranges from 8% to 12% TDS.

In practice, TDS is a diagnostic tool. If your coffee tastes weak or watery, a low TDS reading might confirm that you need to increase your dose or grind finer to increase extraction. Conversely, if the coffee is harsh or bitter, a high TDS might indicate over-extraction. By tracking these metrics, you can make small, deliberate adjustments to your grind size or water temperature, ensuring that every cup you brew hits your personal target for strength and flavor balance.