By Dr Alana Seabrook, Dr Carly Gamble, and Dr Victoria Hughes
Sulfur dioxide (SO2) is a naturally occurring compound produced by yeast as a by-product of alcoholic fermentation. It is commonly added at various stages in the winemaking process primarily for its antimicrobial and antioxidant activity. There are restrictions limiting the amount that can be added in most wine producing countries. Importantly, consumer preferences are also leaning towards minimal intervention or low SO2 wines, whilst still demanding a quality product. As a consequence, producers are carefully monitoring and controlling how much SO2 is added more than ever.
The aspiration method to determine SO2 levels is commonly utilised and an accepted OIV method (OIV-MA-AS323-04A1l; OIV-MA-AS323-04A2). This involves acidification of the sample to liberate molecular SO2, which is then titrated against sodium hydroxide. In the case of bound SO2, the sample is heated to break the SO2 bonds. This is labour intensive, subject to operator variation and is reliant on having a laboratory based set-up.
Colorimetric based measurement of SO2 is possible, and has thus far relied on the use of either benchtop spectrophotometers or autoanalysers. The Absorbance ONE unit is a photometer that can fit into the palm of your hand and is fully portable. We present here the validation data for the Vintessential Free and Total SO2 kits in comparison to both the benchtop spectrophotometer and the industry standard aspiration method. Results show that the portable unit offers results comparable to those of the traditional, laboratory-based methods and therefore offers an alternative that can be used in the vineyard. The Vintessential SO₂ test kits are a fast, safe and easy way to determine the amount of sulfur dioxide in wine samples, without the need for the laborious setup associated with traditional methods. This method provides a novel, fast and easy way to determine the amount of sulfur dioxide in wine, can be used for both white and red wines and does not contain formaldehyde based solutions.
The amount of sulfite present in wine is measured by monitoring the reaction with a colour changing compound (chromogen). The reduction of the chromogen leads to formation of a strongly absorbing compound which can be measured at 340 nm using a spectrophotometer. Samples from the Interwinery analysis rounds were run using both aspiration and Absorbance one (Table A & B)
There is a linear correlation between the Absorbance one method, traditional aspiration and a spectrophotometer as shown in Figure 1 (A) for Free SO2 and (B) for Total SO2. Rigorous testing of the method on the portable Absorbance one for wine, beer and cider show that the method is a fast and reproducible alternative to traditional aspiration (Table 1) The measurement of the activated chromogen is stoichiometrically proportional to the amount of sulfite present.
Figure 1. Absorbance One portable photometer
Table 1. Statistical analysis of method performance using IWAG data from five rounds for Free SO2 (A) and Total SO2 (B).
B
References
Gilchrist A, Nobbs J. Colorimetry, theory. Encyclopedia of spectroscopy and spectrometry. 1999 Jan 1:337-43.
Grant WM. Colorimetric determination of sulfur dioxide. Analytical Chemistry. 1947 May 1;19(5):345-6.
