The standard abbreviation for total soluble solids — the total amount of soluble solids in a product. TSS is measured rapidly by refractometry and expressed in degrees Brix, capturing dissolved sugars, organic acids, salts, and other soluble compounds. It is the food industry‘s key maturity and quality index for fruits, juices, jams, and preserves: harvest decisions, blending, and concentration endpoints are all set against Brix targets. Because TSS correlates with sweetness and flavour intensity, it features in grading standards and purchase specifications worldwide. Regular refractometer calibration against sucrose standards keeps this simple but powerful measurement trustworthy.