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.

When a wine is salty, and why it shouldn’t be

Salty is not a common wine descriptor. That it’s also not a positive one probably goes without saying. As a consumer, it’s also not a fault you’re likely to fret over (I don’t think I can recall ever hearing anyone say something like “Hey, Sarah, does this wine taste salty to you?”) But the fact that wine-producing countries have (widely varying) legal maximums for sodium chloride in wine should tell you something. Salinity is a concern in dry locations when frequent irrigation increases soil salinity, which increases wine salinity, which may add one more to the list of western American winemakers’ concerns. Soil composition often doesn’t translate in the way you’d expect into grape composition; salt is, unfortunately, an exception.

An article in the American Journal of Enology and Viticulture last year mentions Australian growers’ and winemakers’ experience that grapes that taste salty may clock in under the legal sodium chloride limit and vice-versa. Law or no law, obviously no one wants “salty” to show up in their product’s tasting notes. The article reported on an effort to quantify when wine saltiness kicked in and how best to measure it. Most of the non-sodium chloride salts that show up in wine – potassium chloride is notable – register as bitter more than salty. Sodium chloride registers as salty, obviously, but also appears to convey soapy sensations. They were interested, then, both in how much salt it took for a taster to call a wine salty and in the negative impacts of defined amounts of salt on wine flavor.

Their cadre of tasters – enology students at the University of Adelaide with some specialized tasting experience – were able to first identify saltiness in Australian Shiraz and unoaked Chardonnay at .36 to 1.76 g/L with a median of .8 g/L and a lot of individual variation (values were lower for the white wine, higher for the red). The Australian legal maximum of .606 g/L, then, means that some of these folk may sometimes encounter a salty wine; the Swiss limit of .06 g/L, on the converse, seems unwarranted at least in terms of sensory concerns. The researchers also spiked the Chardonnay with several concentrations of NaCl and asked a smaller group of specially trained students to rate their sensory qualities. Those experiments confirmed that at .5 and 1 g/L, added salt dampened perceptions of fruit and added a salty flavor and soapy mouthfeel.

To the Australian researchers, the utility of their findings was in recommending that Australian growers could probably rely on their (quite possibly a bit more sensitive than average) taste perceptions to gauge grape saltiness in the field, in terms of acceptability for the Australian market, but not for meeting more stringent international guidelines. They didn’t comment on the implications of their findings for the reasonableness of those guidelines, though perhaps they go without saying. It does seem plausible that saltiness perception thresholds might vary among people of different nations accustomed to different diets, though this study’s Australian-based results were about on par with previous studies including a few conducted in Japan.

One other interesting implication, for household use. Obsessive molecular gastronomist Nathan Myrhvold has recommended that people try salting their wine as they would salt any other food. This is the same gentleman who suggests that a blender is an efficient tool for oxygenating wine, a more aggressive version of “letting it breathe” in a decanter. Myrhvold suggests a tiny pinch per glass. If one teaspoon of salt weighs about six grams, then 1/10th teaspoon per liter of wine amounts to the Australian limit of .6 g/L. A standard glass of wine is about 150mL. In other words, any realistic pinch will send your glass over the technically established edge. But it’s worth noting that Myrhvold is recommending this as a tactic to make a wine taste more savory.

I tried this with an exceptionally ordinary glass of Australian shiraz. The salt did, indeed, make the wine taste more savory. Frankly, that was neither difficult nor especially unwelcome for something that started off as a bit of a fruit bomb. But – and keep in mind that I was not tasting blind – the potential for that to be a benefit was outweighed by the kind of soapiness you get from having added a bit too much baking soda to your biscuits. In this wine, where the fruit was pretty much what it had going for it, I wouldn’t do it again, but I’m interested to see what happens with the next glass of reasonably lively Chardonnay I come across.

For producers in California, Washington, and other devastatingly dry locales, unfortunately, adding salt isn’t going to be that kind of easy option.

Empirical evidence: organic/biodynamic vit = more textured wines

A six-year comparison of organic, biodynamic, and “low-input” and “high-input” viticulture (three years of conversion, three of maintenance) recently came to fruition in South Australia, courtesy of researchers at the University of Adelaide. The full report is freely available here (and three cheers for research freely shared). It’s 73 pages long, but the conclusions are fairly simple. The most worthwhile among them: in blind trials, experienced wine professionals rated the organic and biodynamic wines more interesting than the conventional versions.

  • Soil health (nitrogen, phosphorus, organic carbon, microbe mass) was most strongly improved by compost, not by any particular management system. All four systems were tested with and without compost.
  • Compost had the single most dramatic positive effect on soil health, no matter the underlying management system.
  • Management system had no consistent effect on vine growth, berry weight, or berry composition.
  • Low-input, organic, and biodynamic alternatives yielded at 91%, 79%, and 70%, respectively, of the high-input condition.
  • Organic and biodynamic wines were more “textural, rich, vibrant, and spicy” than their conventional counterparts. (pH, TA, and color held constant; high-input wines were a bit higher in alcohol.)

Improved soil health with organic/biodynamic management has been demonstrated numerous times over, and so have the benefits of compost. This study was unusual in making compost a separate variable, showing that both organics/biodynamics and compost, separately, were beneficial. The upside here is the attitude, across the study, that conventional growers can benefit from organic techniques even without undertaking a full-on organic conversion.

The downside is that the “organic” and “biodynamic” management used in the comparison are weak compared with what many committed non-conventional growers undertake. How can you practice biodynamics without compost? “Biodynamic” here seems to have meant nothing more than adding the core preparations 500 and 501, a far, far cry from anything Demeter would certify as honest biodynamics. Even the organic system is pretty bare bones: weed control with mowing and cultivation instead of herbicides; no insecticides or pesticides other than copper. (The low-input condition pulled back on the insecticides and some of the pesticides.)

Talking about those lower yields, the researchers make an important point. Very little research has been done on organic or biodynamic cultivation methods. We could develop better techniques within those systems and preserve environment and fruit quality while improving yields. Many organic/biodynamic growers have surely worked out such techniques on a local scale, which leaves a role for scientists to listen to what they’re doing, identify why it works and how/whether it can be generalized more broadly. Some environmentally conscious wine people are happy to pour their big pharma money (or whatever it might be) into projects they believe in with no thought for financial return, but most are trying to support their families as well as their values. Sharing successful organic/biodynamic techniques — say, for weed management, which was the biggest issue in this study — developing them scientifically, and stamping them with a scientific seal of approval so that they’re not dismissed as just those quacky organic people, will help conventional growers improve their weed management tactics, too. Likely, too, with economic benefits you can appreciate even if you honestly don’t care about trashing the environment for short-term gains.

The researchers should have made another point about those yields. Are the high-input yields a reasonable benchmark? Should we buy short-term gains with long-term environmental and social damage? If your business isn’t “sustainable” without using chemical warfare to eke every last grape out of the earth, then perhaps you need to reconsider your business practices in other areas. It comes back to the old resurrecting dinosaurs argument. Just because we have the technology to do something doesn’t mean we should. The wine might even be more interesting.