Reduction

“While foul smelling, H2S is rather harmless since it can be removed with oxygen or copper but the continued production and presence of H2S can lead to more problematic sulfur compounds such as mercaptans and disulfides (garlic, canned corn, rubber etc) which are permanent without very harmful aggressive treatments.” -Kevin Harvey

Sorry if this specific question was somewhere answered in some other related thread, but I was just wondering:

1. If a wine from bottle shows reduction which improves with air and with copper (as in a copper penny), is that apparently “non-terminal” reduction ALWAYS present in the bottle regardless of how many years pass? Is it “stable” in a sense, and will ALWAYS require efforts (air and copper) to reverse it…or can it lessen or worsen in severity in the bottle? And if it improves somewhat with air and copper but still shows some unattractive elements of reduction, will that always be the case? And will that condition most probably be present in all bottles of that wine (unless perhaps if the wines were bottled from individual barrel as opposed to batched), unlike the very different issue of premox which can be hit or miss in any given bottle from a case?

2. How can one interpret tasting notes from barrel OR early from bottle where the critic notes reduction but does not seem terribly concerned and gives the wine a high rating…can a taster reliably distinguish “temporary” reduction from “terminal” reduction when barrel tasting, and if not, would it be wise to shy away from any wine where early tastings noted reduction in order to avoid what could be a very expensive mistake?

(I have looked over some of the previous threads, but I am not sure I still understand the answers to the above questions.)

reductions in wine are akin to following tide… how so, molar SO2 bound and free … as wine ages the chemical reactions polymerization of tannins acids precipitating out… this all takes SO2 and utilize it … sometimes the bound increases and the reduction is stronger , other times the bound SO2 becomes free and reduction ebbs… in my experience reduction happen most distinctively once bottled and in a closed environment … not to say a vat can’t reduce, it can, just that some splashing , racking or other treatments will awaken her up… if only the bottle had an indicator that disclosed the reduction, we would not open and hate that wine on that specific day…

Bump.

My random thoughts, opinions and occasional facts:

Background: Reduction, from a chemist’s perspective, is the opposite of oxidation. From a simplistic perspective, oxidation occurs when lots of oxygen is present (surprise!) and reduction is when little/no oxygen is present (the actual description here involves gaining/losing electrons and atoms changing their ‘oxidation state’, but not sure that’s helpful here…not sure this entire paragraph is helpful, but here it is). Reduction in a wine context refers to chemical reactions that occur when the wine is reduced (aka reductive). Newly fermented wine has lots of complex chemical reactions where these reactions that need an oxygen molecule. Wine is stored in barrels partly because the barrels allow a small/constant flow of oxygen to get into the wine. If, despite this, the wine becomes reduced…these complex ‘oxygen requiring’ reactions will still occur, however a sulfur molecule will take the place of the oxygen molecule (this is a vastly simplified description). The result is complex sulfur compounds called Thiols (they used to be called Mercaptans). Thiols is a large group/class of chemicals that range from the disgusting (skunky, burnt rubber, etc) to the sublime (truffle, etc). So reduction in wine is not a universally bad thing, tho it is risky. These Thiols all have their own ‘perception threshold’, below which you can’t smell/taste it and above you can. Beyond this tho is the smell/taste of Thiols can differ/vary greatly depending on the Thiol’s concentration (above the perception threshold)…which can make their identification and description somewhat tricky. Thiols (some of them anyways) can oxidize into disulfides, which are trickier to get rid of and tend to be more permanent (have have their own smell/taste/thresholds).

Questions in #1: The copper trick will make the Thiols ‘inert’ (not perceivable)…so if the smell/taste persists then it’s likely a disulfide and the wine will never improve (either that or what you’re smelling isn’t a reduction product at all, in which case you’re very likely is good shape).

Giving the wine air will often times mask the Thiol (the perception threshold changes when it becomes oxidized…generally the threshold is higher for the oxidized state, meaning that a higher concentration is required to be perceived at all). So if the wine cleans up with air, partly or completely, then Thiols are/maybe your culprit. If the wine doesn’t improve with air then it might or might not be thiols, disulfides (or something else)…I’d tend to lean toward disulfides being the culprit her tho.

Will the wine improve with age? Disulfides are the ‘blue screen of death’ for wine. Thiols may or may not “age away”. My experience with Pinot is that it generally does age away. I’ve had some reductive wines that, based on wise advice, cleaned up after extra time in barrel and bottle (different situations). Chardonnay appears to be in the same group (assuming it doesn’t premox first).

Will the condition be present in all bottles, or will it be hit/miss like premox? The perception of Thiols, and their ability to ‘age away’ depends (in part) on the amount of oxygen in the wine as it ages (in bottle). So it might be a bit like the premox situation…since corks with higher oxygen transmission rates will make premox-potential wines worse, and reductive wines better (depending on the Thiols in the wine). Also, reduction tends to develop in some barrels and not others…so this assumes the wine was completely uniformly mixed in tank prior to bottling. This is more difficult to achieve than you might think…and there usually aren’t good ways to measure/track this.

Questions from #2:

Interpreting tasting notes: Like all aspects of flavor descriptions in tasting notes, this is very difficult if not impossible. Imo, you’re more likely relying on the critic’s experience smelling the reduction in barrel (or recently bottled) and having it clean up later in life.

Distinguishing between temporary and terminal reduction: This is a tricky business. But, as I implied above, with enough experience and a good memory for flavors/aromas, I believe it is possible to correlate flavors/aromas with reductions that will/won’t go away. Like I said tho, this is a tricky business. Assuming we’re talking about Burgundy (perhaps 2010 Hudelot-Noellat? ), Allen Meadows, John Gilman and Antonio Galloni (insert other experienced critic/review sources here) all seem sufficiently experienced with reduction that I would trust them to mark down a wine that has terminal reduction. Whether you agree a particular wine merits a 92, 95 or 98 (from AM/JG/AG) is separate from the fact that I would expect it’s very likely to get through its reductive issues without issues (note the use of ‘likely’ here, but the only other reliable approach is to avoid reductive wines/producers altogether…or stop buying burgundy (insert other region/wine in question)).

Note that even when a reductive wine completely resolves itself, in my experience it will have some impact on the wine long term…tho it’s generally to the benefit of increased complexity but possibly at the expense of masking Terroir (I’m conflicted about this last part, as it appears that how different wines/vineyards become reduced differs…so perhaps how the reduction expresses itself is as mush a part of the Terroir as it is the winemaking?). It’s a bit like oak in wine. Roty’s Charmes Chambertin generally has a lot of new oak, and tho it seems (in my limited experience) to absorb it all…but it’s not like it turns into the same wine if no oak were used. I believe reduction works the same way.

It appears that Chardonnay is more predictable than Pinot Noir (red Pinot, aka not champagne) in its reductive qualities. Leflaive and Coche Dury, for example, have made producing reductive qualities in their whites into a fine art and a part of their house signature.

Those are my opinions…feel free to correct or disagree (not that I need to state that on this board ).

Thanks Eric that was super helpful, a clear and thorough answer to a well-stated question.