At a recent commercial wine tasting, a friend noticed the person who was pouring the wine putting a penny in the decanter. Never having seen this before, I did some research. There is an interesting explanation here.
In short, when a wine has aromas due to excessive oxidation or reduction – such as a sulfur or a sherry like taint – adding a penny can often alter the chemical reaction and remove the taint.
While it’s simple chemistry, I still found myself a little surprised by this. So when the opportunity arose to test it, I gave it a try. Lo and behold, the sherry like taint in the wine I was trying was magically gone. Note that pennies minted prior to 1982 are mostly copper whereas those after 1982 are mostly zinc. Not sure what difference this might make if any as both zinc and copper can act as reducing agents, I used a copper penny. I remembered something about zinc toxicosis in dogs after ingesting pennies. I figured I wouldn’t put anything in my wine that would kill a puppy.