Stefania and I had an email exchange with a friend in Vermont and we exchanged a lot of good information about sulfur in wine. I've edit the excerpts here:
From our Friend:
I thought I had a mold problem in my cellar? .... I've isolated that it's not the cellar and it's not the glassware, I think I'm super sensitive to something in the wine. I've noticed that it's a smell that's much more prevalent in young wines than older wines,...Also, it's usually a smell that improves with some mollydooker shake, or with a few hours in the decanter. As you know I have trouble describing the smell. So I'm thinking that it's probably something that gets added to wines that dissipates over time. Any idea what it could be?
Sulfur! No doubt about it. From the conditions you describe that's got to be it. Most people think sulfur is going to smell like matchsticks, burnt rubber, rotten eggs (that's Hydrogen Sulfide, a by product of Sulfur) or mothballs. In reality, in the amounts added for most good wine, it smells slightly sweet and maybe chalky or minerally would be a descriptor. I could easily see someone thinking it's mold. It's kind of a sickly sweet smell with a hard tinge, like mold growing on something sugary.
We monitor our SO2 levels pretty closely and I usually bottle at 25-35 ppm of Free Sulfur. Free Sulfur is really what you smell. Over time sulfur in wine will become bound with oxygen or amino acids. That's what happens when you do the Mollydooker shake, or decant. The Free Sulfur is bonding with oxygen and 'leaving' the wine. It also happens with bottle age. Something like Mollydooker, with a pH over 4, they're going to have 75ppm+ of Free SO2.
I'd suggest continue to decant and give the decanter a good swirl or two to expose more of the S02 to oxygen. Something like a Venturi would probably also help. Everyone had different degrees of sensitivity. Stef says that after she's been working in the winery with SO2 she can pick it up easily in any wine and that now having working with it, she can pick it out in wine when it's in elevated levels.
Stef chimes in:
I was digging around for other compounds that also dissipate with oxygen exposure. One thing Steve did not mention was mouthfeel, which would also change after decanting. If the culprit is sulfur, there will be a change in how the wine tastes/feels...from being slightly tart making you salivate more than typical, to being less angular and smoother on the sides of the tongue, and then brightening to more fruit forward observances (that's also a little dependent on the type of wine, but I think we're talking about reds, and most likely cabs)
And I offered a little more advice on the problem:
One thing you might want to check is the pH. The lower the pH, the less SO2 that needs to be added. It's a bit of a crap shoot though still. A lot of wineries just add SO2 out of routine. "Every three months add 20ppm, and 50ppm at bottling." That kind of thing.
Somethings you probably want to avoid are wines under screwcap, wines that have been micro-oxidized, and wines aged in whole or part in tank. Those things all increase the Free Sulfur amounts. This may sound silly but another thing you might want to do is avoid smelling the wine when you first open it. Stef swears sulfur sticks in her nose for hours and effects all the wine she has after exposure. We've started wearing masks in the winery now whenever we handle it just to avoid burning up our noses.and a final though for the blog:
I'm a little reluctant to post about sulfates because so many people have wrong information about them and their effects. 1 in 250 people have a sensitivity to sulfates. You are probably not one of them, nor is your friend who says sulfides give the headaches. For those 1 in 250 people, they genetically lack an enzyme in their digestive system that breaks down sulfates. For those people the symptoms are elevated heart rate, flushing and raised blood pressure. The symptoms dissipate after a few hours. Anyone who has this condition will also be highly sensitive to white bread, broccoli and dried fruits which all have MUCH higher sulfate levels than wine.
If you are not sure, have two pieces of wonder bread. If you don't get a headache, drink more water next time you have wine and a little less wine, you had a hangover.