Spice and sulfur: Recent research news from Australia

Wine Australia’s “research, development, and extension” arm periodically releases briefings on research they’re funding. This month, two of those briefings promise particular interest for folks outside Oz.

Spice (Rotundone)

Short: How rotundone (and the peppery flavors it yields) develops in grapes still lacks good scientific explanations, but scientists are working on it and suspect that it’s a multi-factorial process involving sunlight and air exposure as well as enzymes.

Longer: Not necessarily positive for wine quality, but stellar for talking about how chemistry produces flavor. Rotundone is the “impact compound” behind the peppery flavors prominent in some Australian shiraz (and some other red wines), and rarely does a single compound correlate so clearly with a single and very easily identifiable wine sensory note. The sensory correlation seems simple (caveat emptor: expect it to become more complicated as scientists spend time studying it). How rotundone forms is anything but. A lot of scientific activity (and not just in Australia) over the past year or so has been working out both the chemical pathway (enzymes and intermediates) responsible for rotundone and the viticultural parameters describing where it forms.

A major rotundone conundrum has been why its concentrations seem highest in cooler sites – within the plant, the vineyard, and a region – and yet rotundone characterizes ripe Australian grapes. As is so often the case in scientific conundrums, the confusion may stem from trying to pin causality on the wrong set of variables. Rotundone is formed by an oxidation reaction. Recent work says that that oxidation may be motivated by enzymes, sunlight, or oxygen. Or all three. And so, even if rotundone = peppery flavors is a simple equation, solving X + Y + Z = rotundone is shaping up to be a good deal more complicated.

Expect big rotundone news from Australia in upcoming years. Sussing out a viticultural recipe for maximizing (or minimizing) pepper flavors in shiraz could set up Australian shiraz to do what the Marlborough sauvignon blanc industry has done, creating an international brand around a distinctive flavor profile, fueled by scientific research into how to make those flavors ever more obvious. What that research means for smaller producers who aren’t aiming for those sorts of flavor profiles is a different, and interesting question. 

Sulfur (and copper)

Short: Adding copper to finished wines to remove or prevent sulfur aromas may not work the way everyone hopes it does.

Longer: Wines made with very little oxygen exposure and bottled under screw cap don’t have much chance to blow off smelly sulfur compounds produced via this sort of reductive winemaking. (Why sulfurous aromas are a problem in reductive winemaking involves some complex microbiology that’s summarized well here.) A standard prophylactic against eau de cabbage or rotten egg in your freshly unscrewed bottle is adding some copper before bottling; copper binds to the smelly sulfur compounds and acts as a heavy anchor of sorts, keeping the malodorous molecules from volatilizing, entering sniffable air space, and registering as an undesirable aroma. Adding a copper penny to a sulfurous wine glass is a common parlor trick for confirming that particular wine fault; if you’re really smelling sulfur, in theory, the penny should mitigate the problem.

A nice, simple solution to nasty sulfur aromas would seem to be adding copper to bind to and “lock away” sulfur compounds, then counting on pre-bottling filtering to remove the copper-sulfur compounds.

Problem #1: It seems that filtering doesn’t reliably remove the copper.

Problem #2: The copper-sulfur binding isn’t always stable or permanent, so the copper may go off and do other (undesirable) stuff no one was counting on.

It seems likely that copper additions are useful under some if not all circumstances. The future work – of researchers and winemakers working together, one hopes – is defining “some if not all circumstances” more precisely.

The simple chemistry behind removing wine sulfites

There’s something horrifying about our standard reaction to a food label reading “Contains X” being “Is X bad?” That appears to be the standard reaction to sulfite labeling on wines: they had to tell me it’s there, so it must be bad for me. But it would be unfair of me to harp too much on snap judgments when I feel so much instant distrust toward Üllo just because they brand themselves with this horribly stereotyped photo of four young, attractive entrepreneurs smiling broadly at each other over their glasses.

Üllo promises to take any wine that comes with a “contains sulfites” label and turn it into a kinder, gentler, sulfite-free beverage. (Pardon the irony, but I’m still getting over that photo, and their name.) Just to cover my bases, once again, if you react to sulfites, you react to a lot of foods other than wine, you’re probably a severe asthmatic, and you’ll know. There’s nothing wrong with a tool to remove sulfites per se, but it contributes to this whole myth of their being a good reason why the Ordinary Wine Consumer would want to.

The scientific principle at work here is simple, and Üllo is a miniature version of a tool chemists and biochemists use often. In a complex mixture of many different molecules, some molecules will be selectively attracted to each other on account of unique properties related to their electric charge, shape, and atomic composition. If you want to remove one specific molecule or type of molecule from a mixture, you can pour the mixture through a resin loaded with another molecule that attracts it. Your Favorite Molecule (YFM; or least favorite, if we’re talking about sulfites) will remain trapped in the resin while everything else in the mix falls right through.*

What the Üllo folk did was come up with a “food grade polymer” that uses this principle to trap sulfites and put it in this thingamajig that you can sit over your wine glass. Once all of the polymer molecules are loaded up with sulfite molecules they can’t bind to any more, which is why the little filter that sits in the Üllo cup is disposable. They probably needed to do a lot of tinkering to find precisely the right polymer, so kudos to them on that account.

There are two problems with this simple idea. The first is that it’s not perfect. Some of YFM will always miss being bound up and fall through. Üllo marketing deals with that by talking about “returning” wine to it’s “natural” state, and since yeast naturally produce some sulfites, that leaves them about 10 ppm (parts per million) wiggle room. If you’re one of those rare few with a bona fide sulfite problem, that probably isn’t enough to set you off, though individuals’ sensitivities vary.

The second problem is the converse of the first. Inevitably, some stuff other than the target molecule gets stuck on its way through the filter. Üllo is trying to turn this bug into a feature by noting that you’ll remove unwanted sediment as well as sulfites, though I’d hazard that very few people in the target audience for this product are drinking wines with unpleasant sediments in the first place. I’ve not tried Üllo, so I don’t know how wine tastes after being poured through, nor what besides the sulfites changes in its molecular profile. But no matter how good a job those smiling entrepreneurs did with their chemistry, the wine will sustain some collateral damage. Again, probably not a problem if you’re drinking a commercial wine product to have something to hold at a party, but an altogether different issue if you’re expecting to savor the winemaker-crafted nuance of something special.

Üllo is a clever idea: simple, obvious, the kind of thing that makes you wonder why no one’s thought of it before. It might be a great tool for the gluten-avoiding Yellow Tail-sipping crowd that will feel better knowing their wine is virtually sulfite-free. It may even be a real help to some of those very few people who want to drink sulfite-containing wine but can’t breathe when they do. My problem with it is precisely the same as with gluten-free products. Most people don’t need them. Some of those folk are fooled into thinking gluten-free products are healthier anyway (even though they’re often lower in fiber and sometimes higher in fat and sugar). And while some of them are fantastic, most aren’t, and you’re usually losing something else along the way.

*The point of this exercise is often that you want to recapture a purified version of Your Favorite Molecule (YFM), so separation columns are often designed to be reversible: if you pour a solution of something that binds to the resin even better than YFM, YFM will fall off and come out the other side. When I spent time in a biochem lab working on HIV proteins, we used this technique to isolate specific viral proteins so that we could subject them to more testing.

April 2017:  I’m no longer accepting comments on this post after an ongoing deluge (relatively speaking, I know) of comments on this post telling me that I’m not taking individual’s symptoms seriously. Please note that I’m not telling anyone that their symptoms aren’t real or that they shouldn’t do things that make them feel better. I am saying (in addition to observing the clever chemical principle at work here) is that the best evidence we have at present suggests that sulfite allergies are very rare, and that this product preys on the same notions at the heart of the gluten-free craze: that a molecule which causes a very few people extreme harm is also somehow something the rest of us should fear.

There’s fat in your wine, but the fatty acids are the issue

Oil and water don’t mix (unless you add egg, but then you’ve got an emulsion…and mayonnaise). Wine is essentially water plus alcohol, which doesn’t mix well with oil, either. Since there’s no oil slick layer floating on top of your glass of wine the way fat drops glisten on top of a bowl of ramen, you’ve probably assumed that the wine is fat-free. And if you Google “is there fat in wine?” about 102,000,000 results will tell you that you’re right.

Which is wrong, sort of. Wine does, strictly speaking, include very small amounts of fat. New and improved chemical analyses of New Zealand sauvignon blancs have identified that they at least 25 different kinds of triacylglycerides — the chemical reference for your standard fat molecule: three fatty acids (tri-acyl) bound to a glycerol molecule (glyceride). That’s in addition to an assortment of other fat relatives such as free fatty acids and some waxes.

It’s actually the free fatty acids that are most important here. (Those fats are there in such minuscule quantities that even the jumpiest health journalist can’t pretend there’s anything to jump about there.) They’re present in milligram per liter quantities (so we’re talking less than the amount of sugar found even in truly dry wines) which is enough to make a significant sensory impact on wine indirectly. 

Yeast need lots of free fatty acids to grow well; they’re a major raw ingredient for new cell walls. With plenty of oxygen they can make their own; without oxygen, that particular yeast production line shuts down. Fermenting wine is a mostly anaerobic job for yeast: they get a little oxygen exposure at the top of the vat, a little if the wine is vigorously mixed to keep the skins submerged, but mostly need to rely on the fatty acids initially contained in the grape juice to tide them over. If that source fails, a long and very complicated chain of yeast stress response events kick in, ultimately ending in stuck fermentations, icky aromas, or both. In short, the amount and kind of fatty acids in particular and lipids in general affects wine aroma.

That’s not a wholly unheard-of problem. Overly enthusiastic efforts to clarify white juice before fermentation can pull fatty acids out, too, to the yeast’s detriment. But, ironically, the more common issue is too much of the wrong kind of fatty acid after the yeast have been at it awhile. Lacking the ability to synthesize cell wall components they really need, too much of cell wall molecules they can make (decanoic and octanoic acids) accumulate with toxic consequences. The effect fatty acids have on yeast is a bit like the effect fat has on humans: too much of the wrong kind kills us after awhile, but not enough of the right kind can cause serious problems, too.

But there’s a different and possibly more interesting point to be made here. Lipids originally present in the grape juice affect yeast metabolism, which affects wine aroma, which gives us new places to intervene to make alterations. Adding lipids to South Australian chardonnay boosted production of aromatic molecules: esters, aldehydes, higher alcohols, and volatile acids. The authors of that sauv blanc study speculate that adding specific lipids might be a way to create new, different styles of that so very identifiably aromatic wine.

This information is splendid in two ways. First, it tells us more about that complex and ill-described business of how winemaking works. Second, it may be a way to experiment with new wines. But, third, it could open up one more avenue for adding stuff to make wine fit a particular sensory profile, which we might more generally call “manipulation” and to which many of us* are generally opposed but which fuels the contemporary commercial wine-as-supermarket-commodity industry and supplies inexpensive reds and whites to fit market niche-targeted profiles specifically designed for the glasses of middle-class suburban mothers between 31 and 40 or single 22-29 condo dwellers who prefer to drink wine before dinner with friends on Thursday and watch Orange is the New Black. All wine is manipulated, all wine contains fat, but what that means for any individual case is a different question.



*Assuming, perhaps unfairly, that “us” is mostly comprised of people who prefer to drink and/or help produce unique and expressive wines that rely more for direction on local traditions, personal philosophy, and vintage conditions than Nielsen numbers.