Dear Wine Wizard,
How do I get copper sulfate in accurate diluted food grade form? I would like to treat 5 gallons (19 L) of stinky fruit wine to get rid of the rotten sewer smell.
The Wiz Responds: Copper sulfate solution is one of those winemaking tools that seems to be tough for home winemakers to lay their hands on. It is often used, as you mention, for the treatment of wines affected by “rotten sewer” or a “rotten egg” smell. I think that it’s difficult to find because, luckily, it’s one of those chemicals that most of us only have to use once in a very long while.
Check with your local winemaking supply shop to see if they stock copper sulfate crystals. One good, reliable source for copper sulfate crystals, as well as 1% and 10% solutions pre-made, is Vinquiry, a wine and wine lab supply house and analytical service provider out of California. They can be contacted at Vinquiry, 7795 Bell Road, Windsor, California 95492 or by phone at (707) 838-6312.
As with any wine additive, it is best to experiment with bench trials first. Copper sulfate — 25.47% of which is copper — is legal in the U.S., as long as residual levels don’t exceed 0.5 ppm as copper. To see if copper sulfate will help the off smell in your wine (as stinky wines aren’t always responsive to this additive), I advise conducting a quick bench trial with a 1% copper sulfate solution as per below:
- Label two wine glasses, one as “control” and one as “copper.”
- Measure about 50 mL of the wine in question into the wine glasses.
- Measure out 1 mL of 1% copper sulfate solution into each “copper” glass.
- Swirl each glass, let them sit for about five minutes, then smell each (do not taste as this is quite a bit of copper for 50 mL of wine).
If the copper glass still has the stinky smell, it goes to follow that copper sulfate will not help out your wine — or it could just be you haven’t added enough. For scientific purposes, it’s worthwhile to double the amount to see if it helps. (Keep in mind that 1 mL of a 1% solution added to 50 mLs wine is way over the legal limit of 0.5 ppm as copper).
If you do find that the 1 mL of 1% copper sulfate solution does help your wine, you can perform further bench trials to hone in on the amounts you should use. Too much copper sulfate added can strip the aromas or slightly change the flavor and mouthfeel profile of wines, so it’s always best to add the minimum amount needed. Experiment by trying various levels of the 1% solution in 50 mL samples of wine. (Be sure to dilute it accurately — it helps to have volumetric pipets or flasks as well as a supply of distilled water.) Once you find the level you like, scale up the small-scale amount used to determine how much solution to add to your volume of wine.
Copper sulfate is one of those additives that, hopefully, not many of us winemakers need to use very often. However, when it’s required, there’s nothing like copper sulfate to take the rotten egg smell out.
Order some and be sure to ask for technical literature about hydrogen sulfide (the usual culprit of the rotten egg smell), sulfide detection trials and copper sulfate trials. Of course, prevention is always the best solution to any problem, so take extra care and pay close attention to details in your winemaking before your wine starts smelling like rotten eggs and you will have solved the issue before it arose.