Are there any articles on the chemistry of how sweet wines age?
I went out for dinner on Saturday and picked out some wines to take.
Looking at the stickies I noticed that three splits of 2000 Van Der Heyden Semillon
were looking a remarkably nut brown colour, whereas the 2001 Rieussecs next to them
were all still a pale straw colour. Given that both had been stored in the same unit since
purchase I’d be curious if anyone can explain exactly why the Semillons were so dark
after such a relatively short period.
If only I were rich enough and lived long enough, I would love to learn enough to be able to explain why Sauternes age from a light lemon yellow to a rich mahogany brown, and the flavors that are implied by the color. Unfortunately even though I am a chemist I think I have to admit to being ignorant about this. There is a “browning” reaction, Maillard I think, that is the same thing that happens to toast. But the causes and implications? I dunno.
Doesn’t it have something to do with acidity?
Possibly. The Semillon was certainly on the lighter side in that department.
I posted exactly this question on the Ebob Education forum to see if anyone had a clue. Turned out that the education moderator didn’t know any more than I. So I spent some time looking things up and came up empty except for suggestions like the following:
Oxidation - several different mechanisms for this. SOme of the phenolic compounds are not stable and if there’s molecular oxygen around, they’ll combine. Sometimes it’s a result of enzymatic activity. Botrytis apparently produces enzymes that help this along too, and some metals help catalyze, but I don’t understand that entirely.
Caramelization - some people say it requires heat, others say that it can occur otherwise, and also if the wine was ever pasturized, that can be an issue. Also, if the wine was put into toasted barrels, or even untoasted since the staves need to be heated for bending, there may be some dissolved caramelized sugars in the wood that come into the wine.
Maillard reaction - unlike caramelization, which is based on sugars, this also needs proteins/amino acids. Some people dispute this because they say it requires heat, but other people say it can be caused by enzymatic reactions and can occur slowly at cellar temps. Doesn’t seem to be anything definite. However, there have been studies of melanoidin compounds in wine and some people have also suggested that some precursors are found in the berry skins, particularly in really ripe grapes.
In any case, the breakdown of the sugars causes much more interesting flavors to develop and the flavors seem to hint at all three of the above.
Also, if the winemaker doesn’t want to use much sulfur, the wine is far more likely to brown quickly. It seems to be highly individual and specific to the wine, because slight molecular differences between wines can cause a great deal of change.
And then there’s the issue of the corks and storage. Corks aren’t consistent, being organic products, so you have a range of oxygen ingress across an entire lot of bottles and you end up with different browning of the same wine. Browning seems highly temperature dependent and different storage conditions also matter.
Good question tho and I hope someone can help answer it. Reviewing the scientific literature, at least to my limited brain, doesn’t seem to show anything definitive.
Thanks for all the info, Greg.
On the oxidation, I was told once that sugar acts as antioxidant. That came from a geeky colleague in a camera store who recommended a teaspoon in your Dektol developer to keep it from turning brown if you left it out in the tray!
To my surprise, neither Jamie Goode (The Science of Wine) nor Harold McGee (On Food and Cooking - The Science and Lore of the Kitchen) have anything to say about this in their books, which usually have the answer to everything.
Neither does Jackson or any of the other usual suspects. I ended up going to scientific papers and almost nobody does any research directly on point so you end up looking at everything else that might be related.
Interesting about sugar. Fructose causes increases in uric acid in the body, at least according to the Pauling Institute, and that correlates to increases in antioxidant protection. But regular table sugar as an antioxidant directly? Somehow that doesn’t seem right but who knows.
My guess, based on absolutely nothing other than limited personal observation, is that probably most of the browning is due to oxidation and that’s because of oxygen that was incorporated as part of the bottling or that came through leaky corks. I have a few bottles of Tokaji-aszu that I looked at the other day - same vintage, producer, etc., and one is golden and the other is browning. Has to be the cork because storage was the same. And when Mercedes opened a bottle of 1964 at Tondonia, it was not browned at all.
I was just going to write something on this.
I bought three '88 Rieussecs on release. I had one last year and quite enjoyed it. I am planning on bring one to an OL in a few weeks. I pull out both bottles one is amber as I would expect given its age. The other straw colored?
I have never seen such disparity and can’t image why? Anyone have a guess.
I had 3 bottles of the Van Der Heyden; still have two. The colour on all three of them is the same nut brown, so while not disproving the leaky cork theory all three corks would need to have been equally leaky.
It’s certainly consistent with the ability of very sweet wines to age for decades.
I would have guessed (and I am certainly not equipped to opine intelligently) that it might be oxidation in the case of a bottle that was more amber/brown, but a browning reaction otherwise, since if the darkening occurs very slowing, it coincides with caramel flavors, and those are byproduct of browning.
Well, maybe we can all get some donations together and fund some research? It’s likely a number of reasons.
Dave - does he do that wine every year? Is it a botrytised wine or just late harvest like his cab? I like his stuff a lot.
No, it’s not something they do regularly. This was a 2000, the previous was a 1991.
We moved out here in 1995 and his was one of the first wineries we visited. The 1991 Semillon was one of the most unusual wines I’ve ever tasted; it started off very sweet but on the finish the sweetness just vanished in an instant leaving flavours of nuts - hazelnut and macademia. I’ve never found anything like it before or since, though a friend has told me that some Madeiras do this. I was hoping that the 2000 would do the same, but so far it hasn’t.
I still have a complete vertical of the late harvest Cabernet from 1990 to 2001 (6 vintages made), though we stopped going there soon after Sandy died,
Going back to your original post, Dave, I can think of several possible differences:
– Botrytis concentrates other elements in the wine, including acidity, so if there was more botrytis on the Rieussec, that might be a factor.
– Historically, some Sauternes producers used sulfur dioxide to halt the fermentation. The sulfur would both slow down aging and bleach the wine. I’m not sure, but I think filtering to remove the yeasts is a more common technique in the New World.