As wine oxidizes, it produces - among other things - hydrogen peroxide, which is highly reactive. It can go on to react with many different compounds, but often reacts with ethanol to produce acetaldehyde.
Among different oxidation products, acetaldehyde has probably the biggest impact in wine - the more aldehydic character a wine shows, the more oxidixed it appears.
Unlike some people might think, free SO2 doesn’t really protect from oxygen directly by binding oxygen, but instead readily binds with acetaldehyde, turning it into a compound that either isn’t volatile (can’t be smelled) or doesn’t lend oxidative flavors to wine.
When the wine ages (or oxidizes) and the level of free SO2 drops below a certain threshold, changes in the equilibrium between free and bound SO2 make bound SO2 release oxidation products, making the wine suddenly appear oxidized.
Explained by J. Goode (in my words), from his book Authentic Wine. Does the chemistry seem sound?
“Free SO2 present in wine will prevent this oxidation by reacting with intermediate oxidation products, as well as with the formed acetaldehyde, resulting in a (supposedly) odourless sulphite combination known as hydroxysulphonate, which is stable in the acid medium.”
It’s a far too complicated thing for me to understand completely, and I’m a Ph.D. Chemist. This more technical article is fascinating, and seems to suggest that SO2 reacts with numerous components in wine, and not just the products of oxidation. Frankly, when hydrogen peroxide gets produced, I’m a little doubtful that it will be scavenged first by the small amount of SO2; it seems much more likely to just oxidize any number of higher concentration compounds it runs into randomly.
This is an area I think is one where wine geeks throw out a lot of old wives tales, without much real understanding, and I put myself in that category as well.
Of course, that’s a given. SO2 is used to stabilize wine, it has influence on wine color, it can bind with many volatile compounds making the wine aromatically closed, etc. However, we were discussing oxidation and how SO2 works with that, so I thought it wasn’t necessary to bring up all the things SO2 does.
Frankly, when hydrogen peroxide gets produced, I’m a little doubtful that it will be scavenged first by the small amount of SO2; it seems much more likely to just oxidize any number of higher concentration compounds it runs into randomly.
Where did you read this? What I explained from Goode’s book, hydrogen peroxide most often produces acetaldehyde, as ethanol is the highest concentration compound in wine after H20. Acetaldehyde is what gets scavenged by SO2 and transformed into hydroxysulphonate, not hydrogen peroxide.
2016 Renaud Bruyère & Adeline Houillon Savagnin Arbois- France, Jura, Arbois (26/07/2021)
A little light to begin, some smoke, firm acids. More expressive after an hour. Peach oils, jasmine but very strict, piercing. Really opens up with time, heftier and spicier. Very good.
Thats some serious Jura. Not jealous at all!
But the smoke here is probably down to a reductive approach and not SO2. Do the smoke match into your idea of a matchstick note?
In BC, in the Okanagan wine area in 2015, there were widespread wildfires and they tainted the wines made that year. Apparently grapes are especially susceptible to smoke taint during veraison.
In 2008 Ici la bas made Pinot and Chard from the Anderson Valley. The fires took place during veraison so the skins were coated with ash etc and the red ended up smelling like a campfire in need of some marsh mellows.The color was light. The white was fine if not great. In 2020 vintage I tasted some whites but sometimes it was hard to tell if the wine had been affected by smoke or if it just been too damned hot to make fine wine. In theory pressing should eliminate the smoke taint with whites.
They say brett is possible with whites but I have never seen it.
I could spam about a hundred tasting notes on bretty whites if it helped to convince you.
Brett is definitely more common in reds than whites because it prefers higher pH and SO2 is so much more effective in knocking brett out at lower pH. However, with natural wines that employ no SO2 whatsoever, it’s relatively common to see brett even in high-acid, low pH whites. Not like common common like every white is going to be bretty, but if you drink a lot of natural wines, you’re bound to come across them. Seems especially common in Jura whites.
However, I’ve seen lots of people drink quite bretty and funky white wines without realizing that the wines were bretty, because they’ve only thought that brett is something you see in Rioja or Rhône. Only when I’ve pointed out that the wine is quite obviously bretty, they’ve been like “oh my god, the wine actually IS bretty!”, as if taking a veil off their eyes.
The same thing has happened so many times when I’ve pointed out to people if a wine is mousy. At first they don’t seem to find anything wrong in the wine, but once you’ve learned to taste mousiness, it’s something can’t be unlearned.
Actually, come to think of it, I think I’ve ruined many wines for many people in the course of my life.
I tried a 2018 Aligoté that had been infected with brett. Of course, it had then been fined, filtered, osmosed etc to within an inch of its life, probably making it even worse. It was utterly revolting.
