This has probably been covered before though a quick search didn’t reveal it. Apologies ahead of time for my lazy nature.
Richard’s notes on the Monte Bello vertical mentioned several reductive wines. I have read that a penny or a stirring with a silver spoon can take care of the reduction: “H2S in the wine, quickly converting it into insoluble (and odorless) copper or silver sulfide.”
First of all, a penny doesn’t have enough copper in it to make this happen. But theoretically, a copper implement (strainer, perhaps) that the wine is run through may help if the “reductive” problem is sulfides.
If the problem is disulfides, trisulfides or mercaptans, the chemical bonds differ and the process to decrease their impact must take place in steps - and in the case of mercaptans, usually won’t work sufficiently to eliminate them. Often times, the process tends to strip the wine of desirable aromas and flavors.
BTW, here I use the word reductive as you did - to indicate the presence of sulfides.
That is not a technically accurate definition of the word but it is a short-hand used by many of us for the presence of sulfides.
I’ll leave discussion of that definition for another time.
No doubt that sulfur chemistry can be a challenge (moreso in wine). I didn’t realize that hydrogen sulfide existed in acids (i.e. wine) in that form. Apparently it’s as soluble in wine as water.
Back in my early environmental days, adding acid to an aqueous solution of sodium sulfide could’ve been enough to trigger a plant evacuation. Alkaline sulfide solutions (much safer) were incredibly effective at precipitating out metal salts of all sorts: Fe, Zn, Cu, Mn, Hg, Cd, Pb, Ag etc.
Organosulfur compounds add another layer of complication.
Its a big subject. Reductive wines, or more accurately, wines that exhibit sulphide compound aromas, can range from seductive to disgusting.
The basic science is that H2S is produced by yeast during fermentation when the yeast is stressed due to lack of oxygen (hence the term reductive), low temperatures, lack of yeat-available-nitrogen (YAN) or too much sulphur as a residue of sprays.
The H2S, if not prevented or removed can develop into mercaptans which give the wines aromas coverin forest-floor, compost, burnt rubber, iodine, onions, shrimp and skunk. As yopu can see, some of those increase the complexity and some of them ruin the wine. Some producers pretend those aromas are down to terroir. Which has a grain of truth becuase certain terroirs will give grapes with low YAN. It’s certainly accepted and sometimes praised by critics in France and Europe.
Popping a copper coin in the glass will usually remove the H2S and lower level sulphides but not the more stable mercaptans. It’s a fun party-trick to prove the wine was reduced but will not turn it into a nice one.
Adding copper to wine will precipitate out H2S and mercaptans (except during fermentation, which is a bad idea)…tho it can take a while for the copper and marcaptans to react and precipitate out. Copper won’t have any effect on disulfides unfortunately. Disulfides are an oxidized form of mercaptans…so the disulfides have to be reduced back to mercaptans so you can add copper to take them out (the reward of having successfully taken the disulfides out of wine is that you can now bulk it out…woo hoo).
OK, I’ll bite. Why? Granted, too much copper will kill the yeast, but yeast also metabolize copper. So it seems like the perfect time to add a little copper since the yeast will eat up the residual, leaving the wine copper free. And catching the problem as early as possible keeps the amount of copper needed to the bare minimum.
Apparently, copper in the must can cause yeast to produce more H2S…esp during the growth phase. Perhaps it’s safe to add later in the fermentation (after the growth phase)…I’m not sure about that. Keeping the yeast relaxed and stress free seems best of course.
I’ve only added it near the end of fermentation. Slight H2S smells during the peak of fermentation aren’t totally uncommon for us, and usually blow off in a day or two. But when if remains persistent past that, and can’t be diminished by extra hard punchdowns, that’s when I’ll try a 1ppm add. That usually does the trick.