Q: I have Syrah with H₂S that I tried to take care of with a copper sulfate addition. After doing bench trials I found a solution but when I went to treat the entire batch I was rushing and ended up with 11 mL of 1% copper sulfate in a 15-gallon (57-L) batch. In the middle of the night I realized it was way too much. I have a 1-micron filter, would that help?
— Roger Mattar • Corona, California

A: That’s too bad that you added more copper sulfate than you intended to. Copper is an effective, legal, and ancient (the Romans knew about its curative powers in winemaking) tool for reducing (no pun intended) stinky rotten egg defects. Hydrogen sulfide is often the culprit and ionic copper, delivered in the form of copper sulfate (CuSO₄), can often help the problem. We have to be very careful because though copper sulfate is about 25% ionic copper, residual ionic copper has a legal limit in commercial winemaking (0.50 ppm Cu) because too much copper is toxic. It also can markedly change the nose and finish of a wine so that’s why it’s important to do bench trials to find the minimum dose possible that will affect the change you desire.

Luckily, working out the math, and keeping in mind that copper sulfate is only 25% ionic copper if you’ve added 11 mLs of a 1% solution to 15 gallons (57-L), you’re probably right around that legal limit. You may not have to throw the wine away due to it being toxic but you may very well be disappointed in the taste and smell of the wine after the addition. Unfortunately there’s no good way to remove a lot of excess copper once it’s in your wine. Residual copper can decrease over time if your wine is very leesy; I’ve found with monthly lees stirring I once “removed” (due to absorption onto lees) about 0.10 ppm but this is just my own anecdotal experience. You could certainly blend it (do bench trials first) but one of my maxims is never throw good wine after bad. If you do blending bench trials and like the results, however, you could go for it, especially if you have a lot that could use a little copper sulfate itself.