Determination of free sulfur dioxide in cider

Sulfur dioxide (SO₂) is used in cider production mainly as preservative, but also for other purposes (for example for antiseptic, antioxidant, antioxidasic, solubilizing, combining and clarifying functions). Part of the SO₂ that is added as potassium metabisulfite to cider undergoes a series of reactions. Therefore, after a short period of time, most of the sulfur dioxide reacts with some of the substances present, binds with them and forms addition compounds (combined sulfur dioxide) that are unable to express the typical properties of unbound molecules. Therefore, only the part that does not combine (free sulfur dioxide) plays an important role in preserving cider from oxidizing alterations and from some micro-organisms. This test can be used to determine the fraction of free SO₂.

The analytical method developed for CDR CiderLab, a cider analysis tool, allows to determine free sulfur dioxide (SO₂) in 2 minutes with a simple photometric reading of a sample of cider as it is without having to resort to complex equipment such as those provided by the reference method for separating the analyte from the matrix.

The CDR method avoids the continuous calibration checks of the method necessary for iodometric titration.


Test Principle

Chemical reaction involved in the determination of free sulfur dioxide in cideer and must

The free fraction of sulfur dioxide is made to react with an organic disulphide in order to form a colored compound, whose intensity, measured at 420 nm in kinetics, is directly proportional to the concentration of free sulfur dioxide in the sample.

Calibration curve

The calibration curve of CDR CiderLab, obtained using reference methods.

CDR CiderLab calibration curve for the analysis of free sulfur dioxide in cider, obtained using reference methods. R² = 0.968

Reagent test Kits

Measuring range

AnalysesMeasuring rangeResolutionRepeatability

The Analyzers for process and quality control in cider production


CDR CiderLab

  • Complete analysis panel, supplied already configured
  • Up to 16 determinations simultaneously
  • Possibility of carrying out analyses of the same sample
  • Integrated printer
  • Full connections (LAN - USB - Bluetooth barcode/QR code reader)

CDR CiderLab Jr

  • Partial analysis panel, supplied configured with 3 analyses of your choice, implementable
  • Up to 3 determinations simultaneously
  • Wireless connection to external printer
  • USB connections