Preservatives and antioxidants

Sulfur dioxide: free and total

Both free and total sulfur dioxide can be measured using the Rankine and Pocock aspiration method or by the Thermo Fisher Discrete Analyser (Gallery).

In the aspiration method, sulfur dioxide is sparged from the acidified wine sample in an air stream and trapped in a solution of hydrogen peroxide. The aspiration procedure oxidises the sulfur dioxide to sulfuric acid which is then titrated with standardised sodium hydroxide. The amount of sodium hydroxide required is proportional to the amount of sulfur dioxide.

The free sulfur determination by the Gallery method, is based on the reaction between free sulfur in an acidic medium with a mixture of pararosaniline and formaldehyde to give a pink colour which is measured at 575 nm.

The total sulfur determination by the Gallery method, is performed by diluting with pH 8 buffer, stabilizing, then taking a zero measurement. DTNB reagent is then added, which reacts with a free sulfhydryl group to yield a mixed disulphide and 2-nitro-5-thiobenzoic acid product. This yellow product is measured at 412 nm.

Matrices covered by the Gallery method are: All red, white and rose wines (still, sparkling, high sugar, fortified, and botrytis), beer, cider, spirits, vinegar and water samples.

Ascorbic and erythorbic acids

Ascorbic acid and erythorbic acid function as reducing agents and are used as anti-oxidants in wine production. Commercial Services performs this analysis using High Performance Liquid Chromatography (HPLC). Dehydro ascorbic acid, which results from the oxidation of ascorbic acid, can also be measured.

Sorbic acid

This method involves a colorimetric procedure measuring absorbance after a single extraction with iso-octane. The analysis of this compound is mandatory for all wines that are exported to Japan.

Prices per analysis
Analysis Per Sample (excluding GST) Volume required Total response time
Free sulfur dioxide by Gallery $14.70 10 mL 24 hrs
Total sulfur dioxide by Gallery $14.70
Sulfur dioxide free and total (Gallery) $25.20
Free sulfur dioxide by aspiration $21.00 50 mL 24 hrs
Total sulfur dioxide by aspiration $21.00
Sulfur dioxide free and total by aspiration $31.50
Ascorbic and erythorbic acids $42.00 10 mL 72 hrs
Sorbic acid $27.30 10 mL 24 hrs

For more information, please contact AWRI Commercial Services on (08) 8313 6600 or e-mail commercialservices@awri.com.au