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.

Rotundone: Is there anything new to learn?

Having a spare two days in Auckland last week, I paid an all-too-short visit to Waiheke island which — thankfully, if you’re like me and are always looking for an excuse to get out of a big, crowded city — is only a pleasant 40-minute ferry ride from downtown. While the island is still best known for Bordeaux-style blends, syrah has of late become the island’s new darling. So, as it will when wine science geek meets winemakers in a spicy red zone, rotundone came up.

Rotundone is, quite fairly, one of the better known contributors to wine aroma. Unlike so many other more or less mysterious molecules, rotundone produces a specific, distinct, and very characteristic aroma: the black peppery note we associate strongly with Syrah (or Shiraz, if you’re speaking Aussie). We’ve only had specific evidence of that rotundone-pepper-syrah correlation since 2008, when an Australian group identified the compound, showed it to be the heretofore most powerful wine aroma compound (i.e. the one with the strongest impact at the lowest concentration), and demonstrated that 20% of their experimental syrah-drinkers couldn’t smell it at all even while the other 80% were being overwhelmed. In 2008, it was “an obscure sesquiterpene.” Six years later, I had a winemaker ask me whether there was really anything more to learn about rotundone.

Two articles have been published on how rotundone develops in the vineyard in 2014, both from Australia (including researchers involved in the original rotundone research), both confirming that viticultural practices and vineyard conditions generally can affect rotundone concentrations. One, working from a precision viticulture stance, gave evidence that rotundone concentrations vary across a vineyard in ways that might be related to how soil differences and topography affect temperature. The other showed that rotundone concentrations decreased with leaf pulling (which increases grape sunlight exposure and therefore temperature) and increased with irrigation; dropping unripe clusters (as growers do to control yields and even out ripening) didn’t have an effect.

The winemaker’s point was: “Um, duh? We knew that already.” Whether or not he could, in fact, have predicted all of the details of these experimental results matters less, I think, than that he perceived the research as useless. Vineyards on Waiheke aren’t irrigated. The estate vineyards with which he deals are small enough and local enough for him to walk and taste regularly, observe when and where the peppery flavors he wants (or doesn’t) are happening, and give picking orders accordingly. None of this rotundone research changes what he’s going to do in his vineyard so, to him, it’s pointless.

His comment highlighted a question increasingly on my mind of late. Who is wine research for? It’s obviously for scientists, and there’s nothing wrong with that: knowing about the world is a worthwhile goal on its own merit apart from any specific practical outcomes that knowledge might have, and long live basic research. Scientists and the community at large say that it’s for the benefit of “the wine industry” and, in part, that’s true. For a large operation manufacturing a specific wine style calling for a “dialed in” level of pepperiness and relying on fruit from many vineyards, that rotundone research might change things. Maybe they think about calling for a different leaf plucking regime on some of their syrah vineyards that aren’t quite meeting quality targets. But is the research for small producers, like this skeptical Waiheke winemaker? Call him provincial or even selfish for thinking that research doesn’t continue to help “us” understand more about rotundone, but he still knows what he needs to do to make a syrah that, by all indications, sells like roses on Valentine’s Day, out his cellar door, at prices that folks without the million-dollar views find hard to justify.

The syrahs I tried, at Mudbrick and Obsidian, were pretty convincing. Both relied more on freshness than power to make their case and certainly didn’t lack for rotundone, even minus irrigation and with leaf plucking common across the island. Obsidian’s 2013, carrying enough fruit and tannin for its lightness and brightness to be delightful and refreshing (and a pleasant alternative to the overpowered, clumsy or pretentious syrahs too easy to find in many New World climes), would accompany a sweaty Waiheke summer afternoon as nicely as a grilled lamb chop.

Is there anything more to learn about rotundone? Unquestionably. But, maybe, the more pertinent question for a Waiheke winemaker is whether there’s anything more to be learned about making well-balanced, pleasantly but not overpoweringly peppery syrah. Realizing that those two questions are in fact different is key, I think, to furthering both goals.