What is the TDS in coffee?

In the world of specialty coffee, we often use sensory language to describe a cup, but TDS—Total Dissolved Solids—provides the hard data behind those perceptions. Simply put, TDS measures the concentration of coffee solubles that have successfully moved from the ground beans into your water. When you use a refractometer to check your brew, you are essentially calculating the ratio of dissolved coffee solids to water. A higher TDS percentage indicates a stronger, more concentrated cup, while a lower percentage suggests a thinner, more diluted one.

It is vital to distinguish between strength and extraction. Strength (TDS) tells you how much 'stuff' is in the cup, but it doesn't tell you if that 'stuff' tastes good. You could have a cup with a 'perfect' TDS that tastes sour or bitter because the extraction process was flawed. This is why professionals use the SCA Brewing Control Chart to balance TDS against extraction yield, ensuring the coffee is neither underdeveloped nor over-extracted.

For the home brewer, TDS is a powerful diagnostic tool. If your coffee consistently tastes watery, your TDS reading will likely be low, signaling that you might need to increase your coffee-to-water ratio or grind finer to increase surface area. Conversely, if the coffee feels heavy or harsh, a high TDS reading might confirm you are over-extracting. By tracking these numbers, you move from guessing to precision.

However, remember that TDS is not a measure of quality. A coffee can sit perfectly within the industry-standard range of 1.15% to 1.35% for filter coffee and still be unpleasant if the beans were stale or the roast was poor. Use TDS as a compass to help you replicate your favorite recipes, but always let your palate be the final judge of whether the cup is truly delicious.