Introduction

Sulphur dioxide has been added as a preservative to alcoholic drinks for hundreds of years. They are referred to as "Sulphites". The amount added is strictly controlled by legislation.

Recently it has caused much concern because sulphites in wine can cause health effects. Because of this, manufacturers are trying to reduce the concentration of sulphur dioxide.

Methods to calculate the sulphite concentration have been developed, this allows them to confirm that the drink contains enough preservative to be kept fresh for a reasonable time, but it won't affect the taste and it won't exceed the legal limits.

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The Aim of the Experiment

The aim of this experiment was to investigate the different sulphur dioxide concentrations in wines from different countries around the world and compare these concentrations with European legal limits of sulphur dioxide in wine.

Two wines were used in this experiment, a Colombard Chardonnay (JP Chenet) from France, and a Colombard Chardonnay (Banrock Station) from Australia.

Method

To determine the total SO₂ in the wine (free SO₂ + combined SO₂), 25cm³ of sodium hydroxide solution (1 mol per litre) and 25cm³ sample of wine was measured with a pipette and put into a 250cm³ conical flask.

The conical flask was swirled gently and left to stand for 15 minutes. 10cm³ of sulphuric acid (2 moles per litre) and 2cm³ of starch solution was added to the flask.

0.002 moles per litre of iodine solution was used to titrate. It was added until the end point was reached, indicated by the blue/purple colour that stays for 2 minutes. 

The experiment was repeated until concordant results were obtained, then the titration was carried out again with a different sample of wine. 

In this experiment, Colombard-Chardonnay was used, one from France (JP Chenet) and one from Australia (Banrock Station).

Results

Colombard Chardonnay - France (1st Titration)

Titration	1	2	3
Start	14.9 cm3	5.4 cm3	13.5 cm3
End	40.6 cm3	31.2 cm3	38.2 cm3
Total	25.7 cm3	25.8 cm3	24.7 cm3
Average (Of Concordant Results)	25.75 cm3

Colombard Chardonnay - France (2nd Titration)

Titration	1	2	3	4	5	6
Start	7.8 cm3	0.8 cm3	10.3 cm3	0 cm3	0.4 cm3	0.2 cm3
End	33.3 cm3	26.2 cm3	37.4 cm3	25.3 cm3	25.6 cm3	25.7 cm3
Total	25.5 cm3	25.4 cm3	27.1 cm3	25.3 cm3	25.2 cm3	25.5 cm3
Average (Of Concordant Results)	25.38 cm3

Colombard Chardonnay - Australia (1st Titration)

Titration	1	2	3
Start	0.2 cm3	7.7 cm3	0 cm3
End	31.2 cm3	38.3 cm3	30.7 cm3
Total	31 cm3	30.6 cm3	30.7 cm3
Average (Of Concordant Results)	30.65 cm3

Colombard Chardonnay - Australia (2nd Titration)

Titration	1	2	3	4
Start	13.7 cm3	0.1 cm3	4.3 cm3	0.3 cm3
End	48.7 cm3	29.2 cm3	33.4 cm3	29.5 cm3
Total	33 cm3	29.1 cm3	29.1 cm3	29.2 cm3
Average (Of Concordant Results)	29.13 cm3

The Calculation

An average of the concordant results was used for these calculations.

France

SO2 (aq) +  I2(aq)  + H2O(l) ----> 4H+(aq) + SO42-(aq) + 2I-(aq)

1 mole -> 1 mole


SO2 (aq) :                                                                                                                                                I2(aq):

Moles                 5.113 x10-5                         Moles                    5.113 x10-5

Litres                  0.025                                Litres                     0.025565

Concentration   0.002042                       Concentration       0.002

grams per litre = gfm x concenration
          
                            = 64.1 x 0.0020452
                    
                            = 0.3109732 g/L

milligrams per litre = grams per litre x 1000

                                    = 0.13109732 x 1000

                                    = 131.09 mg/L

Australia

SO2(aq) +  I2(aq)  + H2O(l) ----> 4H+(aq) + SO42-(aq) + 2I-(aq)

1 mole -> 1 mole

SO2 (aq) :                                                                                                                                               I2(aq):

Moles                 5.978 x10-5                         Moles                   5.978 x10-5  

Litres                  0.025                                Litres                     0.02989

Concentration   0.0023912                     Concentration       0.002

grams per litre = gfm x concenration

          

                            = 64.1 x 0.0023912

                    

                            = 0.15327592 g/L

milligrams per litre = grams per litre x 1000

                                    = 0.15327592 x 1000

                                    = 153.28 mg/L

Conclusion

In comparison, the French Colombard Chardonnay had less sulphites in it than the Australian Colombard Chardonnay.

The EU law says that the limit of sulphites for white or rose wine is 210mg/L. 

(www.morethanorganic.com/sulphur-in-the-bottle)

This shows that the French wine has less preservatives in it, but both wines are within the EU limit.

Evaluation

The titration was done many times for each wine until a pattern of concordant results were obtained. An average was then calculated from those concordant results.

The sodium hydroxide and wine solution was left to stand for exactly 15 minutes each time, and accurate measuring equipment was used.

The equipment used was relatively accurate. Burettes and pipettes were used to measure out the wine and the iodine solution because they were the critical chemicals in the reaction, but the measurements may have been unreliable because different people measured out volumes and so there may have been different judgements. A measuring cylinder was used to measure out the sulphuric acid, which is not very accurate, but this does not affect the experiment because it is not a critical chemical in the redox reaction.

The experiment could have been improved, however, because it was difficult to judge the end point of each titration, so the volume of iodine used could be more or less than the stated amount used.
To minimise end point errors, a sample was kept at the side, and every titre was left to stand for a couple of minutes, before we compared them with the sample and judged as a group whether it had reached the same end point or not.

The experiment could be extended if we carried out titrations from a range of colombard-chardonnay wines from each country to see which country has, on average, more sulphite in their wine.