A fairly common correction that has to be done in winemaking is to treat sulfurous aromas that are the by-product of fermentation. Often the aroma will blow off during racking, but sometimes they linger and without treatment can produce troublesome mercaptans or disulfides. Luckily, copper reacts almost instantly with sulfides and removes the smell (if you’ve ever seen a distillery, they use copper tubing for the same effect.) In the winery, we use a copper sulfate solution so that we can precisely control the amount added.
With any addition to the wine, we want to make certain that we are adding only the amount we need. To do this, we prepare a bench trial. In this instance, we lined up six beakers of the red wine and precisely filled them to 100 mL. The first beaker is left untouched and acts as our control. Then the second beaker gets a .05 ppm copper addition, the third a .1 ppm addition, the fourth a .15 ppm addition, and so on.
When all of the additions have been made, we cover them securely and wait as long as needed for the reaction to occur, in this case overnight. One of my favorite things about the copper trial, though, is that there is an immediate improvement in the aroma of the wine, and I could sense that even a .05 ppm addition of copper would be adequate to remove the sulfurous aromas. For the 700 gallons of wine that I am treating, it means I will only need to add about 1.5 teaspoons of 10% copper sulfate solution. It’s very effective!
I will be treating this wine very soon, then will also do a bentonite treatment as well. This will grab the copper molecules that have bound with the sulfur and settle them to the bottom of the tank, keeping them out of the finished wine.