Ah yes, Monday morning quarterbacking is always tough when it comes to wine. Adding a complex yeast nutrient (a mix of nitrogen, amino acids, and other micronutrients) is something I do with every fermentation. I have the luxury of being able to send my musts and juices to a wine lab to measure their amino acid and nitrogen content, but even when the available nitrogen levels are sound (about 300 ppm YAN or yeast assimilable nitrogen) I still add a tiny bit of a DAP-free complex yeast nutrient mix to make up for any deficiencies but not further increase nitrogen levels. Indeed, it’s most often a lack of nutrition that makes a fermentation, and the resulting wine, smell like rotten eggs (hydrogen sulfide).
Adding copper is certainly something that can help, but, rather than dumping in bits from the hardware store, next time use measured and metered amounts of a copper sulfate solution (CuSO4). You can buy CuSO4, along with directions for use, from many winemaking suppliers. Because too much copper can be toxic to humans, and because it seems like you have over-added, I must caution you to not drink this batch of wine. There is the possibility of using hydrogen peroxide to remove residual copper, but this Hail Mary is usually reserved for commercial winemakers who have to salvage a batch for economic reasons. The cure can sometimes be worse than the disease; hydrogen peroxide is a powerful oxidant and can ruin your wine just as equally as excess copper can. You could send a sample to a wine lab like ETS Labs (www.etslabs.com) to have it tested for residual copper but testing is expensive. Your easiest, cheapest, and safest bet is to throw out this batch and start again. Adding copper is best done by using the smallest amount of copper sulfate solution you need to make the needed aromatic improvement, then making the addition and testing for residual copper afterwards to make sure your wine is safe to drink.
