Now revised and updated
One of the most common tests conducted in the juice manufacturing industry is the measurement of soluble solids by refractometry. It is not only used for the assessment of a quality parameter but it is also commercially important where used in yield assessment. IFU method number 8 describes this method. The principle is that the dry soluble solids content of a sample is estimated from its refractive index, with reference to the refractive index of a pure sugar solution. The refractive index is proportional to the solution concentration (following the theory of Lorentz and Lorenz). In fruit juices the refractive index is therefore dependent upon sugar concentration and also upon the concentration of other soluble materials (organic acids, minerals, amino acids etc.).
The method has been recently revised to include a weight per litre table.
The correction of soluble solids for malic/tartaric acid and salt is still under discussion but will be available in the near future.
Keep your test methods up to date download IFU #8: www.ifu-fruitjuice.com