A comparison study of total acidity methods for the analysis of wine

Comparison of total acidity methods for wine — Application Note 71720

Significance of the topic

Total acidity is a fundamental compositional parameter in winemaking and quality control because it affects taste, stability and microbial risk. Different jurisdictions and laboratories use different titration end points and procedures, which can produce systematically different results. Rapid, accurate and automatable methods that correlate with established reference procedures are valuable for routine laboratory throughput and consistent process control during production of wine, cider and liqueurs.

Objectives and study overview

The study compared an automated colorimetric Total Acids method (Thermo Scientific Total Acids, Wine pH 7) implemented on a discrete photometric analyzer with the OIV reference Total Acidity method (OIV-MA-AS313-01), which is the common European approach using potentiometric titration or titration with bromothymol blue and comparison to a color standard. The goal was to evaluate correlation, recovery, throughput and suitability of the automated colorimetric approach for a range of alcoholic beverage matrices.

Methodology and experimental design

• Methods compared: OIV Total Acidity Type 1 (OIV-MA-AS313-01) — potentiometric or bromothymol blue titration up to pH 7.0; and Thermo Scientific Total Acids — automated colorimetric assay using bromothymol blue indicator (color change over pH 6.0–7.6).
• Colorimetric assay details: assay uses a buffer and bromothymol blue; absorbance read at 620 nm with a side wavelength at 700 or 750 nm to correct for scattering/bubbles; results calculated from an automated calibration curve and expressed as g/L tartaric acid (1.0–18.0 g/L) or g/L sulfuric acid (0.5–12 g/L).
• Samples: a selection of white wines, red wines, spiced (mulled) white and red wines, ciders and a liqueur; concentrations ranged from 2.65 to 8.82 g/L (as tartaric acid). No sample pretreatment or predilution was performed prior to analysis.
• Calibration and standards: five-point calibration performed automatically on the analyzer using a laboratory-prepared tartaric acid standard (Sigma-Aldrich 251380) with automated dilution.

Used instrumentation

• Thermo Scientific Gallery discrete analyzer — automated photometric platform for the Total Acids colorimetric assay and for running multiple colorimetric/enzymatic methods in parallel.
• Thermo Scientific Total Acids (Wine, pH 7) reagent kit.
• Laboratory-made tartaric acid calibration standard (Sigma-Aldrich).

Main results and discussion

• Correlation and recoveries: the automated colorimetric Total Acids method correlated well with the OIV titration method. Recoveries for the set of samples ranged from 91% to 112% (i.e., automated results were within ±9% to +12% relative to the OIV reference), with no clear systematic bias related to sample color or acidity across the tested matrices.
• Sample-specific performance: measured concentrations spanned approximately 2.65–8.82 g/L (tartaric acid equivalent). Individual sample biases were generally small; for higher-acidity samples some negative bias was seen (example: 7.86 g/L reference vs ~7.18 g/L automated, recovery ~91%), but this was not uniform across the dataset.
• Throughput and automation advantages: the Gallery analyzer processed 26 samples in under 18 minutes. A five-point calibration with automated dilution completed in ~2 minutes 30 seconds without operator intervention. The method requires less operator skill and hands-on time than manual titration.
• Analytical robustness: the measurement design includes a side wavelength to mitigate effects of bubbles or scatter in cuvettes. The authors report that matrix color did not produce a consistent interference for the matrices tested (white/red/spiced wines, cider, liqueur).
• Multiplexing potential: the discrete analyzer allows other colorimetric or enzymatic assays (e.g., glucose, fructose, acetaldehyde, total polyphenols, calcium, sulfur dioxide) to be run simultaneously, increasing laboratory efficiency.

Key takeaways and practical benefits

• The automated Total Acids colorimetric method provides a rapid, user-friendly alternative to traditional titration, with good agreement to the OIV reference across common wine and related beverage matrices.
• High throughput and low hands-on time make the method suitable for routine QA/QC and process-control laboratories in wineries, cider houses and liqueur production.
• Automated calibration and dilution reduce operator error and improve reproducibility of routine measurements.
• Because the OIV definition excludes carbonic acid and sulfur dioxide, and because different standards (e.g., AOAC uses a higher endpoint pH) exist internationally, laboratories should ensure their chosen method aligns with regulatory or labeling requirements for the market of interest.

Limitations and considerations

• Endpoint definitions differ internationally (OIV pH 7.0 versus AOAC pH 8.2), so numerical results can vary depending on the chosen standard; harmonization or conversion factors may be required when comparing data across regions.
• Although no color-related bias was observed in this sample set, other matrices or extreme chromatic interferences could require additional validation or matrix-matched calibration.
• The colorimetric method reports total acidity as tartaric acid equivalents; laboratories that require specific acid speciation (e.g., individual organic acids) must use other chromatographic or enzymatic assays.

Future trends and potential applications

• Greater adoption of automated discrete photometric platforms for routine enological analyses, enabling consolidated workflows and simultaneous multi-analyte panels.
• Integration of inline or at-line sensors for continuous monitoring of acidity during fermentation and processing, combined with discrete analyzer checks for validation.
• Improved chemometric correction algorithms and wavelength-selection strategies to extend colorimetric methods to more challenging matrices.
• Moves toward harmonization of international acidity reporting standards or software tools that enable conversion between end-point conventions to support global trade and regulatory compliance.

Conclusion

The automated Thermo Scientific Total Acids colorimetric method delivered results that correlated well with the OIV reference titration across a representative set of wines, spiced wines, ciders and a liqueur, offering fast throughput, low operator burden and the ability to multiplex additional assays on the same analyzer. Laboratories seeking efficient routine total acidity monitoring can adopt this automated approach, provided they validate method performance for their specific matrices and consider regulatory endpoint requirements.

References

1. Darias-Martin J, Socas-Hernández A, Diaz-Romero C, Diaz-Diaz E. Comparative Study of Methods for Determination of Titratable Acidity in Wine. Journal of Food Composition and Analysis. 2003;16:555–562.
2. Compendium of International Methods of Analysis. Wine and Must. Method OIV-MA-AS313-01:R2003.