In the second part of our lab session we looked at the use of copper sulphate fining to remove H2S from red and white wine. The copper sulphate reacts with the H2S to form copper sulphide that is highly insoluble, therefore careful lab trials should be done before any copper sulphate additions as the residual unreacted copper can cause sulphide problems in bottled wine.
The materials required to conduct the trial was 5 tasting glasses, 250ml of the wine that needed treatment and a copper sulphate stock solution and pipettes. The addition rates of the copper sulphate solution when then calculated leading to mass confusion to descend on the class we all got different answers but this was eventually cleared up as we realized that it was in fact the amount of CU2+ (copper) that we were looking for now the amount of copper sulphate.
The wine was then measured out into each glass and the correct amount of copper sulphate was added to the glass in increasing increments. Each glass was then assessed for the presence of H2S aroma. The targeted fining rate would be the one that removed the aroma and was the lowest amount to do so.
For my results I found that the treatment of 0.1mg/l was more than enough to remove the H2S aroma and anything more than that caused an overload which resulted in a strong aroma of copper overpowered every other aroma.
Another problem arose when another group appeared to have been using tainted glasses, as they had neither H2S aroma nor a copper aroma. Instead their glasses smelt heavy of Brettanomyces a common wine fault but not really what we were looking for in this trial. So that made for an interesting discovery.
Coetzee, C. (2017, March 23). The ins and outs of a copper fining trial. Retrieved December 11, 2020, from Vinlab: https://vinlab.com/blog/2017/03/22/the-ins-and-outs-of-a-copper-fining-trial/