Simple wine analysis

Importance of the Topic

Wine quality and safety depend on precise measurement of key chemical parameters. Monitoring pH, total acidity, sulfur dioxide content and reducing substances such as ascorbic acid ensures product stability, flavor balance and regulatory compliance.

Objective and Study Overview

This study outlines a step-by-step procedure for the simultaneous determination of pH value, total titratable acidity, free sulfurous acid, total sulfurous acid and reducing compounds in wine using potentiometric and bi-voltametric titration techniques.

Methodology

Sample preparation requires no pretreatment except for degassing carbon dioxide when measuring sulfurous acid. Analyses include:

• pH measurement with a combined glass electrode calibrated at pH 4 and 7.
• Titration of total acidity to pH 7 using 0.1 mol/L NaOH in SET mode.
• Free SO₂ determination by acidification with H₂SO₄ and titration with 0.00260 mol/L KIO₃ in MET Ipol mode.
• Total SO₂ after alkaline hydrolysis with 1 mol/L NaOH, followed by acidification and titration as above.
• Quantification of ascorbic acid and other reductones by bi-voltametric titration with KIO₃ after addition of glyoxal to suppress SO₂ interference.

Used Instrumentation

• Automatic titrator with MET and SET modes
• Double platinum sheet electrode and LL Unitrode with Pt1000
• 20 mL burette and magnetic stirrer
• Standard buffer solutions (pH 4 and 7)
• Reagents: NaOH, H₂SO₄ (25 %), KIO₃, KI, glyoxal solution (40 % w/w)

Main Results and Discussion

Typical analytical ranges observed in wine samples are:

• pH: 3.3–4.0, with values above 3.8 indicating potential quality issues.
• Total titratable acidity: 4.0–6.5 g/L expressed as tartaric acid.
• Free SO₂: 20–100 mg/L, varying by wine type and origin.
• Total SO₂: 160–450 mg/L, higher in white and dessert wines.
• Reducing substances including ascorbic acid: method detects total oxidizable compounds; selective DPIP titration recommended for pure vitamin C.

Electrode maintenance and calibration protocols are critical to ensure reproducible endpoints and to avoid membrane drying or fouling.

Benefits and Practical Applications

• Rapid, multi-parameter testing within a single work-up.
• High accuracy and reproducibility suitable for quality control in wineries and analytical laboratories.
• Compliance with regulatory limits on acidity and SO₂ content.

Future Trends and Potential Applications

• Integration of automated titration systems with inline sampling for continuous monitoring.
• Miniaturized sensor arrays for field testing and on-site quality assurance.
• Coupling potentiometric titration with spectroscopic detection to improve selectivity for specific reductones.
• Development of chemometric models to predict quality attributes from combined titration data.

Conclusion

The described potentiometric and bi-voltametric methods provide a comprehensive toolkit for routine wine analysis. When properly calibrated and maintained, these techniques deliver reliable data on acidity, sulfur dioxide levels and reducing substances, supporting product quality and safety.

References

1. Zakharova E.A., Moskaleva M.L. Potentiometric determination of the total acidity and concentration of citric acid in wines. Journal of Analytical Chemistry, 2011, 66(9):848–853.
2. Application Bulletin 98: Determination of ascorbic acid (Vitamin C) and its compounds.