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

Significance of the topic

The accurate determination of total acidity in wine and other alcoholic beverages is a critical quality-control parameter that affects flavor, stability, fermentation control and regulatory compliance. Different analytical definitions and end points (OIV vs AOAC) and methodological choices (titration vs colorimetric/enzymatic) produce divergent numerical results, so harmonized, rapid and robust assays that correlate with reference methods are valuable for production laboratories, control bodies and research settings.

Goals and study overview

The study compared an automated colorimetric Total Acids method implemented on a discrete photometric analyzer with the established OIV Total Acidity Type 1 titration method (bromothymol blue indicator). Objectives were to evaluate correlation and recovery across a variety of alcoholic beverage matrices (white/red wines, spiced wines, cider, liqueur), to assess throughput and operational advantages, and to determine whether the colorimetric approach can replace or complement titration in routine winery and laboratory workflows.

Methodology

The OIV reference method measures titratable acidity by titration up to pH 7.0 using NaOH with bromothymol blue as indicator (or potentiometric titration). The Thermo Scientific Total Acids colorimetric method uses bromothymol blue color change (yellow to blue) between pH ~6.0 and 7.6; reaction absorbance is read at 620 nm with a side wavelength (700 or 750 nm) to correct scattering or bubble artifacts. Samples are mixed with buffer and color reagent; the analyzer applies an automatically generated calibration curve (calibrant: tartaric acid) to report results expressed as g/L tartaric acid (measuring range 1.0–18.0 g/L tartaric acid; 0.5–12 g/L if expressed as sulfuric acid). No sample pretreatment or predilution was performed in the study. A five-point calibration with automated dilutions was completed in ~2 minutes 30 seconds.

Instrumentation used

• Thermo Scientific Gallery discrete photometric analyzer (automated sample handling and colorimetric measurement).
• Thermo Scientific Total Acids (Wine, pH 7) reagent kit for colorimetric total acidity.
• Tartaric acid calibration standard (Sigma-Aldrich) prepared and dispensed automatically by the analyzer.

Samples and pre-treatment

Test set comprised white wines, red wines, spiced white and red wines (mulled wines/glögg), cider and liqueur, with total acidity values (by OIV reference) spanning ~2.65 to 8.82 g/L expressed as tartaric acid. Samples were run directly without chemical or volumetric pretreatment.

Main results and discussion

Method comparison showed good agreement between the automated colorimetric Total Acids method and the OIV titration reference. Recoveries of the automated method versus OIV ranged from approximately 91% to 112% across individual samples, with no systematic bias related to sample color or acidity within the tested set. Typical measurement precision was illustrated by replicate readings with consistent absorbance values at 620 nm and stable calculated concentrations. Key practical performance points:

• Correlation: acceptable agreement with the OIV method across wine types, cider and liqueur in the tested concentration range (2.65–8.82 g/L).
• Throughput: rapid analysis—26 samples in under 18 minutes—indicating strong productivity advantages over manual titration.
• Workflow: minimal hands-on time; automated calibrations and dilutions significantly reduce analyst effort and skill requirements.
• Interferences: using a side wavelength to correct for bubbles/optical scatter reduces matrix-dependent artifacts; no color-based trend was observed in the sample panel.

The study demonstrates that an automated colorimetric variant of the OIV indicator-based approach can reproduce titration results reliably for the matrices and concentration range tested, while offering improvements in speed and ease of use.

Benefits and practical applications

• High-throughput routine screening of total acidity in winery QC, blending decisions and end-product release.
• Reduced requirement for operator titration expertise and lower per-sample hands-on time.
• Integration with multi-analyte workflows on discrete photometric platforms (e.g., simultaneous assays for sugars, acetaldehyde, polyphenols, calcium, SO2), enabling consolidated testing streams.
• Automated calibration and dilution streamline method validation and daily QC procedures.

Limitations and considerations

• The study covered a moderate concentration range (2.65–8.82 g/L); performance at the extremes of the stated measuring range (1.0–18.0 g/L) should be verified per laboratory needs.
• Though no color or matrix bias was observed in this sample set, unusual matrices or very turbid/particulate samples may require confirmation or minimal sample clarification.
• Regulatory definitions differ (OIV pH 7.0 endpoint versus AOAC pH 8.2); laboratories must ensure the chosen method meets the applicable legal or trade standards for reporting total acidity.

Future trends and potential uses

Advances likely to influence total acidity analysis in alcoholic beverages include:

• Greater automation and multiplexing on discrete analyzers to deliver comprehensive compositional panels from a single sample aliquot.
• Improved spectral correction algorithms and dual-wavelength approaches to further reduce matrix effects and enable robust direct analysis of turbid or colored samples.
• Miniaturized and portable colorimetric or spectrophotometric devices for at-line winery measurements to accelerate production decisions.
• Harmonization efforts between regulatory methods (OIV, AOAC) and development of validated equivalency data sets to support method substitution.
• Integration of chemometric calibration and quality-control dashboards for continuous performance monitoring and rapid corrective actions.

Conclusion

The automated colorimetric Total Acids method implemented on a discrete photometric analyzer closely matched OIV titrimetric results for a representative set of wines, cider and liqueur, with recoveries of ~91–112%. The approach offers clear operational advantages—higher throughput, lower operator skill demands, and compatibility with multiplexed assays—making it a practical alternative for routine laboratory workflows. Laboratories should, however, validate performance across their specific sample types and ensure alignment with applicable regulatory endpoints.

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.