The aim of this trial was to determine what type of reductive compounds are causing a wine to have a reductive wine fault or character. The wines were assessed by aroma only.
The reagents used were:
- 1% w/v Copper (II) Sulphate solution
- 1% w/v Cadmium (II) Sulphate solution
- 10% w/v Ascorbic acid
The method was carried out as per laboratory manual. The aroma was compared, and the table below was used to interpret our results.
I did not pick up on the presence of an offensive odour in the control wine, I also did not notice a change in the aroma between the different treatments. It was revealed that the reductive compound was Dimethyl sulphide (DMS). As a fault DMS is described as having a ‘vegy’, ‘asparagus’ or ‘cooked corn’ aroma. The treatments used do not have an effect on DMS (as seen in table 1), therefore it makes sense that the aroma did not change.
In completing this trial it emphasises the need to have winemakers who are able to recognise faults even when present in small amounts. Although I did not pick up on the fault in the control wine, some consumers may detect the fault and this will discourage them from purchasing their wine.
The cooked cabbage aroma identified in the control wine is characteristic of both mercaptans and disulphides. The addition of copper in glass 2, and the addition of ascorbic acid + copper in glass 4 removed the reductive wine fault. Disulphides cannot be removed through the addition of copper alone, therefore we can deduce that the reductive wine fault in this trial was mercaptans.
The rotten egg aroma identified in the control wine is characteristic of H2S, it is also characteristic that the Copper addition in glass 2, and the Cadmium addition in glass 3 would remove the H2S fault. Although the addition of ascorbic acid + copper removed the rotten egg aroma, a new fault was detected. Glass 4 had a noticeable sweet aroma, and we were informed that the addition of ascorbic acid could have oxidised the acetaldehyde in the wine. This sweet aroma was not observed by some of my other classmates, therefore it could have been a result of unintentionally adding a larger volume of ascorbic acid.
Why carry out this test?
The principle of this test is that different reductive wine characters react with different fining agents, including copper and cadmium salts. Depending on which fining agent removes the undesirable aroma the type of reductive fault can be identified. In a winery setting this trial would be carried out to determine whether any reductive sulphur compounds are present in the wine, and consequently specific measures would be taken to remove the fault in the wine.