TDS stands for Total Dissolved Solids and is a measurement of the amount of “stuff” or soluble solids in a liquid. In coffee, TDS reflects the level of extraction and the presence of dissolved solids in the water. The TDS of water is measured using a refractometer, which calculates the degree to which light is refracted by the liquid and compares it to an index to give a percentage extraction. TDS provides valuable data for coffee roasters and baristas to control extraction, resulting in a well-balanced coffee with a good level of complexity and sweetness. The use of TDS technology in coffee has evolved from analyzing water to measuring brewed coffee, leading to more interesting insights.