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Food & Beverage analysis

Optimisation of sulphite analysis in wine using a method validated against the official method

Although some yeasts can produce sulfites in small quantities, winemakers also add them deliberately to help the wine maintain its quality over time.

Why is sulfite added to wine?

Although some yeasts can produce sulfites in small quantities, winemakers also add them deliberately to help the wine maintain its quality over time. It is a compound that currently has no substitute, although its concentration can be reduced with additives. Sulfur dioxide (SO₂) plays a key role in winemaking thanks to its three main functions:

• Antioxidant: prevents wine oxidation
• Antimicrobial: inhibits bacterial growth
• Anti-enzymatic: slows down enzymatic reactions responsible for color changes

Total sulfite in wine is divided into combined and free forms. When SO₂ is added, part of it combines with sugars, aldehydes, and polyphenols, while the rest remains free. This free sulfite protects the wine against oxidation and microbial contamination.

Why is measuring SO₂ so important?

Monitoring sulfite levels in wine is essential for several reasons:

• To track the decrease of sulfite during aging (due to diffusion, oxidation, or binding) and determine how much needs to be added.
• To avoid excessive concentration, which can cause unpleasant flavors and aromas or inhibit malolactic fermentation.
• Wine regulations in many countries set maximum sulfite limits and often require labeling when sulfites are present.

Methods of analysis

Traditional methods for sulfite determination include:

• Monier-Williams / Aeration–Oxidation (OIV Method OIV-MA-AS323-04A).
• Ripper / Potentiometric Titration (OIV Method OIV-MA-AS323-04B)

However, these methods have some drawbacks:

• They are time-consuming — analyzing a single sample can take up to 25 minutes. For each of the total and free measurements, if only one piece of equipment is available, it would take about 50 minutes for a single sample.
• They require trained personnel and regular equipment maintenance.
• Interferences can occur, affecting the precision and reproducibility of the results. As mentioned before, it is essential to measure both free and total sulfite and performing these analyses using the official method requires a significant investment of time and resources. For this reason, having fast, validated and reliable automated methods is a great help to oenological laboratories.

The BioSystems solution

Biosystems has developed a method for determining total and free sulfite that overcomes these limitations.

The system’s automation allows up to 15 samples to be analyzed in just 25 minutes. It is a fast, reliable, and robust method that considers color and other potential interferences, delivering results with high reproducibility and repeatability.

The validation process was carried out in collaboration with wineries and reference laboratories worldwide. The method demonstrated excellent performance compared to the Aeration–Oxidation Method (OIV-MA-AS323-04A, Type II method)*.