TDS

TDS (Total Dissolved Solids) in coffee brewing refers to the concentration of dissolved coffee compounds in the final brewed liquid, expressed as a percentage. It is the primary measurement of brew strength — how concentrated or dilute your coffee is. A higher TDS means more dissolved coffee material per unit of water, producing a stronger-tasting cup. TDS is measured using a refractometer, a small optical instrument that passes light through a coffee sample and calculates the dissolved solids concentration based on how much the light refracts.

The SCA recommends a TDS range of 1.15% to 1.35% for brewed coffee, which corresponds to the strength range that most people find most balanced and enjoyable. Espresso operates at a much higher TDS — typically 8% to 12% — because of its concentrated nature. A TDS below 1.15% generally tastes thin and watery, while above 1.35% the coffee can taste overpoweringly strong and harsh. These are guidelines, not absolute rules — personal preference varies, and some brewing traditions (Turkish coffee, Nordic-style filter) deliberately target TDS outside the SCA range.

TDS and extraction percentage are related but distinct measurements. TDS tells you how strong the brewed coffee is. Extraction percentage tells you how much of the coffee's soluble material was actually dissolved from the grounds. You can have a high TDS (strong) with a low extraction (under-extracted but concentrated, as with a ristretto espresso) or a low TDS (weak) with a high extraction (over-extracted but dilute). Understanding both numbers together gives the most complete picture of what happened during brewing.

For home brewers, a refractometer is a useful but non-essential tool. Many specialty coffee enthusiasts use one to dial in their recipes and verify that their technique produces consistent results. Basic coffee refractometers are available in an accessible price range and can measure TDS in seconds with a single drop of coffee on the lens.