If you are anything like me, you have managed to wing your way through numerous vintages without knowing what you are doing, relying on others know how and patience to show you. In this blog we are going to look at how to conduct a copper fining trial to remove H2S, Mercaptans or just ‘clean up’ a wine, so hopefully when the time comes, one can be confident and self-reliant in the cellar.
Copper sulphate or CuSO4 is an additive used to clean up H2S/Reductive aromas in a ferment or wine. It can be used in red or white wines and is commonly used in most wine making regions in the world. We use copper solution because the copper ions bind with the sulphur ions and drop out of solution, taking the H2S aromas with it. If there is any residual copper sulphate left in the wine, it can be removed when racking or filtering. For this reason it is unadvisable to add copper sulphate just before bottling.
Why bother to conduct a copper trial? Why not just add it? We need to find the correct amount of copper to add that will give use our desired results. We need to know the lowest possible rate of addition because Copper Sulphate is highly insoluble and unreacted copper has the potential to cause sulphide problems in bottle – the exact opposite of what we are trying to treat. Adding too much can have a negative effect, stripping thiols and delicate aromas. Also, we must remember that some countries have restrictions on the amount or do not allow copper in the wine, so if we are exporting, we need to be careful (for example the amount of Residual Copper permitted by the EU is < 1 mg/L and the USA < 0.5 mg/L)
How to conduct a trial:
You will need:
5 tasting glasses
250mls of wine needing treatment
0.1% copper sulphate (CuSO4) stock solution = 0.0255 Cu2+
A ‘tasting’ team
measure out 50mls into each glass
Calculate the amount of stock solution needed in each glass
Pipette CuSO4 into each glass
Table 1: Copper addition rates. 0.1% copper sulphate (CuSO4) stock solution = 0.0255 Cu2+ (C1)
|Addition rate (mg/l) of CU2+||Control (C2)||0.1||0.2||0.3||0.4|
|Volume (ml) of stock solution to add to 50ml of wine (V2)||control||0.2ml||0.4ml||0.6ml||0.8ml|
* A helpful way to work out the addition rates is to use the following equation (practice maybe needed to understand this) V1 = V2xC2/C1
Using a micropipette, accurately pipette the correct amount of copper stock solution into each glass
Gather your ‘tasting’ team and assess each glass for the presence for H2S/off aromas
Determine the lowest fining rate which achieved your desired results.
*Please note, it is important to have a team of tasters- One person might be highly sensitive to H2S aromas, and another not so much, so the more the merrier to gain a broader perspective.
Now that the trial is done, and the addition rate has been decided on, we can add to tank.
If you are lucky enough to have a mixer/agitator on your tank turn it on, drop in a subbie, or get a pump: either way get your tank mixing, rolling. Add copper mixture from overtop, dripping in the solution slowly. Often putting a small hole in a container with a handle and hanging it from the lid is a time efficient way of doing it.
And there you have it, job done! Start to finish.
I would like to take the time to share what I thought was a very interesting thought: If we used brass equipment ie fittings, pipes, pumps etc in the winery, would it reduce the need for adding copper sulphate?
Better cellar handing everyone
Sulphide Lab: Copper fining trial to remove H2S (n.d) NMIT bachelor of Viticulture and Wine production.
Vintessential Laboratories www.vintessential.com.au/
Rankie B. (1989) Making Good Wine. Sun Books. A manual of winemaking practice for Australia and New Zealand. Pg 281
Copper Sulphate: alibaba.com
copper pipes: Todays homeowner.com