When wine grapes are medicine, forgotten varieties deserve a second look

Autocthonous, adj. – Indigenous to a particular environment, habitat, or geographical area.

Italy, like other places that have vineyards substantially older than their nationhoods, mothers a gobsmacking number of unique, local, autocthonous grape varieties known only to village natives and sleep-deprived MW students obliged to memorize them all. At the risk of offending, most aren’t famous for good reason. International grape varieties (cabernet sauvignon, merlot, riesling, and the like) become international in part because they grow well in diverse locales, in part because of accidents of history, but in part because they tend to make darn good wine. Even as the recent fashion for weird, little-known, and hard-to-get wines means that hyper-local varieties are hearing their names uttered in distant lands (like London and San Francisco wine bars), they’re a niche interest at best.

Nevertheless, lots of scientific work has recently been going into documenting these autocthonous grape varieties. A cynical observer might attribute that to the necessary technology being newly cheap and still trendy, a less cynical one to our renewed appreciation for biodiversity. We could even end up rediscovering lost talent and invigorating new wine styles, like finding the greatest novel of the 20th century as a manuscript in the bottom drawer of your great-aunt’s writing desk and giving it the publication run it always deserved. While we’re waiting for that to happen, there’s actually a different and you might say nobler motive at work. Biologists are hunting for medically useful compounds, and Frosinone in Latium in Central Italy has become their new Amazon rain forest.

Italian biologists have been scouring their countryside for “local, ancient ecotypes” and, beyond the usual business of documenting whether they’re genetically unique, a recent paper takes the extra steps of measuring their concentrations of antioxidant phenolic compounds and observing their effects against proliferating cancer cells. Having first ranked their 37 autocthonous Frosinone varieties by anti-oxidizing and free radical-fighting capacity, they threw concentrated seed extracts at model cancer cells growing in lab dishes. And some of the cancer cells died or stopped growing!

Now, dead cancer cells floating in dishes are clearly a very, very, very long way from wine grape seed extracts being used as the next cancer-fighting miracle drug. But. Compounds from wine grapes likely will (continue to) be investigated as medications. And no matter whether Zimavacca or one of the numerous unnamed “new genetic profiles” from this study become the trendy new somm-bait, we have good reasons to preserve such things. Analyzing samples from odd nooks about the countryside shouldn’t need economic justification: preserving our cultural-biological history is a good fight. But in the present climate, a little economic justification doesn’t hurt.

Melatonin: Regulates your sleep cycle, regulates grape ripeness cycle

Short: Spraying melatonin on vines increases grape size and tightens up the time window over which grapes ripen so that there’s less variation in °Brix across the whole vineyard on any given day. This was just one study in merlot vines, but melatonin could well become a useful viticultural tool.

Longer: Melatonin is a lot more versatile than the little bottles on “natural supplements” shelves suggest. You’re probably familiar with the hormone as something you take to relieve jet-lag or to help you fall asleep on-schedule if you have insomnia. Animals naturally produce the stuff, and so do plants. We know less about what it does in our leafy companions than our furry ones, but research over the past decade has been outlining some kind of role for melatonin in plant growth regulation. It’s structurally similar to auxins, used for decades to increase yields for table grapes which, together with recent studies using it on other fruits, led some Chinese researchers to try spraying melatonin on wine grapes.

14 year-old merlot vines were sprayed with melatonin twice, ten days apart, before veraison (July). The researchers also tried spraying vines just once; spraying twice had a more significant effect. Melatonin-treated vines bore slightly larger berries, possibly a negative for wine quality. But treated grapes also ripened more evenly, a boon for growers trying to harvest as many fully and evenly ripe berries in a single pass as possible. Untreated grapes came in at 16-25 °Brix and twice-sprayed grapes at 18-23 °Brix (eyeballing their graphs), with alcohol content in the resulting wines about even across the board. The researchers also documented some changes in a whole range of aroma compounds that are a bit too up-and-down to warrant saying much, but they suggest that melatonin probably has positive wine sensory effects, increasing ripe/spicy notes (perhaps in part thanks to more even ripening?)

This is one of those “early studies” that happens long in advance of a technology actually hitting the market. But if these results play out in other varieties and other locations, melatonin might well be a reasonable commercial prospect. It seems to have low (if any?) toxicity, be easy to apply and, I suspect is reasonably easy to produce. And (though I shouldn’t make light of the damage vineyard and farm workers suffer from exposure to toxic sprays), treatment for accidental exposure might just be going home for a nap.


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.


Brett + bacteria = worse, or better

Microbiology has gotten a lot wrong studying yeast and bacteria. We’ve assumed, until quite recently, that if a microbe doesn’t grow in a dish it’s not there. And that a microbe is either on/live/growing or off/dead. And that we can study microbes in isolation — “pure culture” — away from other species in little sterile dishes and expect them to behave normally. In all fairness, microbiologists have sometimes seen these as a problems, but have mostly just gone on this way, writing books about what we think we know.

DNA detection and sequencing technology is showing just how many bugs don’t grow in dishes — “high throughput” technology can document (theoretically) all of the species in a drop of [insert favorite liquid here]. That’s pretty routine these days. And we’re slowly beginning to study how mixtures of microbes — you know, the way they live in the wild — behave in the lab. Wine was a bit ahead of the curve here: microbial enologists have been studying the goings-on of spontaneous and mixed fermentations since the late 1980’s.*

Usually, mixed-microbe studies are about what grows where together. Occasionally, you can predict something more specific with a bit of logic and some scratch paper. That, plus a little knowledge of yeast and bacteria metabolism, leads to an interesting hypothesis: some malolactic fermentation bacteria should make Brett smell worse.

Brettanomyces bruxellensis (aka “Brett,” aka barnyard-stench spoilage yeast) creates its signature aroma by converting hydroxycinnamic acids (HCAs) naturally present in wine to smelly volatile phenols. This is a two-step process. First, an enzyme (a decarboxylase) converts HCA to a vinylphenol. Second, a different enzyme (a reductase) converts the vinylphenol to the volatile ethylphenol, including the Brett signature 4-EP and 4-EG.

But before that can happen, Brett has to be able to get to the HCAs. Many of the HCAs in wine are chemically bound to tartaric acid. Brett can’t use them if they’re bound. The HCA-tartaric acid bond spontaneously and slowly breaks, giving off free HCAs for Brett to use, but there’s theoretically a much bigger pool of pre-stink molecules that need only lose their acid first.

Some lactic acid bacteria — like the ones that commonly perform the malolactic fermentation (MLF) so important to most reds and a lot of white wines — can enzymatically split HCAs from tartaric acid. In theory, that should mean that some (but not all) MLF bacteria are Brett enablers. Wine + bacteria + Brett = worse smell than wine + Brett alone.

Building on previous research, a team at Oregon State University has made that more than a theory. Their recent paper (currently pre-press in AJEV) shows that some commercially available MLF strains make more HCAs available than others, AND that leads to Brett making more 4-EP and 4-EG,

The team only experimented with one strain of Brettanomyces, and they obviously couldn’t test anywhere near all of the MLF strains on the market, but this (plus the multiple studies that have come before it supporting the effects of lactic acid bacteria on HCAs) is strong evidence indeed that winemakers buying commercial bacteria for MLF may have better and worse choices if they’re worried about Brett.


*A good open-access (no paywall) example of this kind of research is Granchi and company’s 1999 study here.

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.


High alcohol wines dial down your brain (but does it matter?)

My April piece for Palate Press pokes at the question, “how can we really tell what we’re tasting” by removing as much of the subjective mess around language as we can and going straight to the brain. Using functional magnetic resonance imaging — stop-motion shots of your brain in real time as you perform some kind of task, like tasting wine — we can look for differences in what parts of your brain are active when you’re sipping on wine A versus wine B and infer something about what effect they really have on you. Variations on the theme let us ask all manner of interesting questions. Make wine A and B the same, but tell tasters that one’s expensive and one’s cheap. Brain reward centers will light up more in response to the “expensive” wine. Or keep the wines the same and change the people. Trained sommeliers think demonstrably more and more analytically about wine tasting than casual sippers. Or try to pair up wines to be as similar as possible save for their alcohol level and ask whether tasters prefer the higher or lower alcohol versions.

Okay. The last one is  a stretch. Scientists have done it and shown that higher alcohol wines provoke less brain activation than their lower alcohol counterparts. That’s interesting, particularly because researchers expected the opposite. Instead of more intense wine provoking more intense sensation, it seemed that tasters had to work a bit harder to pay more attention to the subtle nuances in the less hit-you-over-the-head reds.

Okay. I suspect knowing this doesn’t change much for you if you’re a winemaker, but perhaps if you’re running complex formal tastings — either for sensory science experiments or to train sommeliers or diploma students — you now have more evidence to back using lower-alcohol wines to improve students’/subjects’ learning and focus.

But, can we say anything at all about whether tasters prefer the lower- or the higher-alcohol versions? Here’s where they’re stretching. Specific types of brain activation tell us things about pleasure, no doubt: we’ve identified “reward centers” and “pleasure centers” and we can even visualize people drawing associations with memory and emotions (perhaps you’ve made the acquaintance of your amygdala?). But to say that, because higher alcohol wines “dial down” the brain, relatively speaking, tells us nothing about what you should drink when you’re trying to maximize the pleasure of that evening out at the restaurant you’ve been anticipating for weeks.

Far too many other factors come to bear upon wine preference for us to imagine that these study results say much (if anything) about it. My somewhat embarrassing preference for light-bodied Willamette Valley pinot noir is a good example. I appreciate and enjoy virtually everything (just because I’ve never tasted a white zin I could enjoy doesn’t mean it couldn’t exist), but I have a soft spot for raspberry and pine and ocean spray-scented, fine-boned, earth and mushroom-framed pinot. Like the ones I grew up on as a kid scampering around a big front yard abutting a vineyard on Cooper Mountain. I have so many pleasant memories associated with that style of wine, long conversations with my father, warm evening light spreading across the great big round dining room table he made, and mud squishing through my toes while I picked the green beans that I’m going to prefer it, even if it turns out that they require less cognitive attention, even if every critic tells me that they’re poorly made, even if I learn to assess quality by other criteria.

Duh. I haven’t said anything earth-shattering. And, in one way, the difference between a marketing study and a neuroscience one is whether that gestalt gets captured in overall “behavior” or whether one factor is isolated and analysed. The neuroscience is still useful for describing how wine works (something marketing studies rarely do well, to be honest). But it does squat for speaking to complex behaviors made up of scores of these bitty considerations which we need to remember aren’t anywhere near as binary and are a whole lot messier than simple science like this fMRI study makes them seem. So let this be a counterpart to all of the enthusiastically reactionary science journalism that responds to press releases about people drinking wine in giant magnetic tubes by shouting “Science discovers high-alcohol wines aren’t really as good after all!” from their collective rooftop. Nope. We’re not there yet.

One more reason why wine is good for you, and not just the red stuff

When it comes to health benefits, red wine tends to get most of the credit.

Cardiovascular benefits have been ascribed to alcohol itself (find a reasonably readable and full-text review here, courtesy of the Journal of the American College of Cardiology). But, of late (as in, say, the past decade), resveratrol has attracted the most attention; as a potent antioxidant, it truncates the chain of events involved in endothelial plaque formation (“hardening of the arteries”). Resveratrol is much more concentrated in red wine than in white. But resveratrol is a polyphenol, one of many. And polyphenols in general, and both red and white wine, have circulatory system benefits in lab studies we can ascribe to other causes.

For instance, NO, which is to say nitric oxide. Polyphenols encourage artery-lining cells to produce more NO. We know NO both as laughing gas and as a potent (if short-lived) vasodilator. NO tells the artery muscular to relax, which increases vessel diameter and lowers blood pressure. Arteries that no longer relax properly are a feature of many cardiovascular diseases and part of the cascade of interrelated faults that progressively damage both the heart and organs like the kidneys and eyes that suffer damage from blood pressure that’s consistently too high. NO also helps makes platelets less sticky with the effect of gently working against that damaging plaque formation.

Antioxidants, including polyphenols, increase NO levels indirectly by countering oxidative molecules that can rapidly destroy NO in the bloodstream. Polyphenols also stimulate NO production directly, and arteries benefit by learning to relax and suffering clogs less readily.

A paper just out in PLOSOne (always and ever open access) convincingly adds to evidence that caffeic acid, a polyphenol in which white wines are particularly rich, increases arterial lining NO production. The research team demonstrated that caffeic acid increases NO, but also that it improves arterial cell function and slows kidney disease damage in mice. Translating caffeic acid-dosed mice to white wine-dosed humans is still a leap we’ve not yet made, but it’s a likely one. Doses mice received were along the lines of what a moderately-drinking wine lover might ingest, and these sorts of mouse experiments have worked well to model human arterial disease in the past.

In short, there’s a good argument to be made that white wine is good for your heart. As good as red? That’s going a step too far, and not least of all because individual wines vary so much in their concentrations of resveratrol and caffeic acid and total polyphenols that we’d need to compare individual wines rather than try to stereotype by color. But the next time someone tries to talk you out of a glass of Chablis or riesling in favor of the red option for the sake of your health, don’t let them. You know more than they do.

In other news: three useful-if-not-groundbreaking reviews arose in recent days, on biotech uses for winery waste products, causes of and solutions for protein hazes, and polyphenols found in oak. Details are here.

Studying sulfur dioxide effects with better DNA technology suggests we may not need much of it

Fast: In a new study using better-than-ever microbiology, 25 mg/L SO2 added after pressing was enough to “stabilize” yeast and bacterial growth during fermentation, and higher concentrations actually seemed to slow fermentation. Inoculating the must with commercial S. cerevisiae had a very similar effect, even without adding SO2, which looks really, really good for no-added-sulfur wines. BUT (and this is a big but) the study only included one wine (a California chardonnay) made in one way, in smallish (19 L) lab volumes. Goodness only knows if their results will generalize, but let’s hope this encourages someone to look.

More: Sulfur dioxide is the single most commonly used winemaking chemical worldwide. That familiarity probably has something to do with our not understanding it better: we know it’s safe, we know how to use it, and so we don’t have much reason to study it.

In all fairness we do understand SO2 well, but microbiology keeps changing. The publishing dynamo* of Nicholas Bokulich and David Mills – responsible for really excellent recent research on how microbes are spread around a working winery over space and time – plus UC Davis wine microbiologist Linda Bisson (and another Davis student and a Japanese collaborator have published a new American Journal of Enology and Viticulture article on how SO2 affects bacteria and yeast populations in fermenting wine.

The question isn’t new, but the technology they’re using is. Short story: better DNA detection techniques let them pick up on the presence of a bigger range of both bacteria and yeast than previous strategies.

Longer story: Microbes in wine (and elsewhere, for that matter) can be “viable but nonculturable” (VBNC), a new idea ten years ago when microbiologists could still think that agar and Petri dishes were a reasonable way of identifying bugs in a sample. Until better DNA technology made clear a serious issue: yeast and bacteria might be stressed out enough by environments (like wine) to not grow on command but still be alive and able to multiply and cause problems, aka VBNC. (The unculturables who won’t grow in dishes at all are trouble, too.) The details of the high-throughput DNA sequencing they used to ensure that VBNC bugs weren’t left out of their survey aren’t important except to note that it lets them detect more microbes than previous studies.

The other great = new element of this study is its looking at multiple SO2 concentrations, from 150 mg/L down to nil. More work for them; more data for everyone. They also included ferments inoculated with commercial S. cerevisiae and not, which ended up being important.

Their results say that the most important factor in determining what grows in fermenting wine seems to be the degree to which a single strain has the opportunity to take over. One way of encouraging dominance is inoculating with commercial yeast: it more or less takes over and overall microbe diversity declines. But another way is adding SO2, which knocks down some microbes and gives tolerant ones (S. cerevisiae strains included) an opening. Adding SO2 and inoculating S. cerevisiae even without SO2 had similar effects on overall microbial diversity. And, moreover, 25 mg/L was enough SO2 to “stabilize” the ferment. In other words, sulfur-free wines may be less risky than winemakers are generally inclined to believe if they inoculate (which plenty of people inclined not to use sulfur are also inclined to avoid).

The obvious problem: one wine, one vintage, one set of processing techniques, and 19 L volumes. All of these are major reasons to question whether these results will hold for any other set of circumstances. pH and a slew of sulfur-binding compounds affect SO2 efficacy. Fermentation temperature, oxygen, clarification, means of harvesting…the list of processing steps important to microbial diversity is too long to list. And it’s well-known that fermentation volume is important to microbial kinetics.

In short? This article is almost certainly more important to wine microbiologists as a methods paper than to winemakers. (It’s not incidental that the methods section abbreviates the winemaking protocol — “grapes were harvested, crushed, and pressed according to standard winemaking procedures,” whatever that means – and uses nearly a full page of text to describe the DNA sequencing technique.) Nevertheless, it may well serve as impetus for more experimentation with low- and no-sulfur wines, and a good reminder that we always have more to learn about SO2.

Even more: find the full paper, with many more details on which specific yeast and bacteria species were detected and when they peaked (unfortunately behind the AJEV‘s lovable paywall) here. Read the full paper if you can; it contains plenty of potentially idea-generating details that I’ve not even attempted to summarize here.

*Hackneyed maybe, but, seriously, what else do you call them? Bokulich’s CV, as a PhD student, could put to shame plenty of tenured professors. When I’m not just feeling horribly inadequate, I’m wondering where this guy will end up post-graduation. Barring his speaking French and fancying living overseas – or starting a lucrative consulting firm – he’s probably lined up to make tenure at Davis in record time. Heck, he probably already qualifies for tenure.

The value of cold soaks for red winemaking; the value of cold soak research for winemakers

Cold soaking seems to be an especially divisive winemaking technique, at least in the Pacific Northwest, and that’s saying something in an industry full of strong personalities. Cold soakers say that allowing crushed red grapes to rest for one to several days in an environment too cold for Saccharomyces activity, before warming everything up to yeast-pleasing temperatures and allowing fermentation to begin in earnest, deepens color and augments flavor and tannin extraction. The anti-cold soak camp claims that these benefits aren’t real and sometimes adds that cold soaks allow for the dangerous possibility — dangerous, that is, if you’re also in the anti-spontaneous ferment camp — of illicit microbial growth before winemakers inoculate commercial yeast strains at the soak’s end.

Research to date has been unhelpfully mixed. Some studies show increased phenolic (color and/or tannin) extraction, some don’t, some even show lower phenolics following cold soak, and the variables responsible for the differences haven’t yet been worked out. Adding to the confusion is the inevitable mess that follows pro-spontaneous from anti-spontaneous fermenters, since the non-Saccharomyces activity that might occur during cold soaks is a source of desirable complexity to some and unconscionable spoilage to others.

I would love to say “until now” and herald the arrival of a brilliant, conclusive paper outlining a robust explanation for how and why and where and when cold soak works. My inability to do so isn’t likely to come as a surprise. Nevertheless, there is new research and, while far from once-and-for-all conclusive, it helps, if perhaps not in the expected way. A new study from an Argentinian team* tested cold soak on cabernet sauvignon, merlot, syrah, pinot noir, malbec, and barbera d’asti, looking for differences both when the wines were pressed and after a year of bottle aging. Cold-soaked wines saw four days of 6.5-11.5ºC (44-52ºF) courtesy of periodic dry ice additions, then 10-day fermentations at 21.5-26.5ºC (71-80ºF); control wines went straight to 14-day fermentations. All varieties were made in the same way: same full twice-daily pump-overs, same twice-daily punch downs. All were inoculated with the same commercial yeast strain five hours after crush. Regrettably, the study didn’t include multiple variations on the cold soak theme — different times, temperatures, or techniques — that might have helped to suss out where any cold soak differences are happening and given much more information to winemakers. In particular, it’s important to emphasize that chilling with dry ice meant as much as a 10ºC (18ºF) difference in temperature between different parts of the tank because the dry ice clumped. Jacketed tanks would have applied a more uniform treatment.

The agglomerated results were straightforward enough. Cold soaks increased color density, but didn’t increase phenol or tannin concentrations. Cold soaking also didn’t make a statistical difference to any basic wine chemistry parameters: ethanol concentration, pH, acids, glycerol, and residual sugar. Tasters found that the most important difference between all of the wines was driven by grape variety, though that’s hardly meaningful and says nothing about cold soak. That’s the big picture.

The details in the supplemental data attached to the main paper show something more interesting. Each variety responded a bit differently to the cold soak treatment. In the barbera and the syrah, tannin concentrations actually were higher in the cold-soaked wines. The opposite was true for the pinot noir, where cold-soaked wines measured tannin concentrations statistically significantly lower than the control. Cold soaking related to increased total phenols in cabernet, decreased in pinot noir.

What this says to me is that we’re measuring the wrong construct at the wrong level of detail. Asking whether “cold soak” works seems to be the wrong question. Instead, we need to be testing out different potential cold soaking parameters in specific grape varieties to identify what precisely makes a difference and what is moot. This is the kind of data that could really help winemakers who through the lens of their communal experience are saying that cold soak sometimes makes a noticeable positive difference and sometimes doesn’t, and who might reasonably look to science to help them figure out what features separate the worthwhile instances from the useless ones. Unfortunately, if the research question continues to be “Does cold soak increase phenol concentrations?” instead of “Under what conditions does cold soak make a difference to phenol concentrations?” we’re likely to continue seeing confused yes-no-or-maybe reports instead of useful, applicable explanations of what winemakers seem to observe.


*Including Federico Casassa, who has in the past published excellent phenol-related research with James Harbertson at Washington State University, including the American Society of Enology and Viticulture’s 2014 Best Enology Paper of the Year, on the phenolic effects of extended maceration and regulated deficit irrigation, the full text of which is freely available here.

Authenticating icewine: closer, if not quite close enough

Scenario #1 – You’re sitting next to your fire after dinner, relaxed, with a few ounces of fine Canadian or German icewine, maybe a few slices of blue cheese and a ripe comice pear, and the current evening reading book. You enjoy all three for an hour or so and retire, happy and sleepy, to bed.

Scenario #2 – You’re sitting next to your fire after dinner with a few ounces of icewine and an active mind in search of a target, maybe two active minds if you have a companion. Conversation turns to the wine, how desperate those first Germans must have been to salvage their inadvertently frozen grapes and how arduous and expensive repeating the process on purpose now is. You speculate that cutting real icewine with something else must be mighty tempting, and the gaze you cast on your glass turns wary. And then you cast your gaze on Google and find this new article in the American Journal of Enology and Viticulture on a new strategy for testing the authenticity of icewine.

Icewine production is very expensive and no International Body of Icewine Authenticators polices producers to ensure that they’re doing it right or in good faith. Canada produces the bulk of the world’s stock (though I also enjoyed some fine examples in the Finger Lakes, not too far south of Ontario), and the Canadian Vintner’s Quality Alliance (VQA) legislates use of the term: a Canadian bottle with “icewine” or “ice wine” on the label must be made from approved varieties, from grapes harvested during “sustained” temps of at least -8°C, naturally frozen on the vine, coming in at at least 35°Brix, with no added sugar or alcohol, all overseen by a VQA representative. European producers employ similar standards, but the Asian sweet wine market is apparently well-populated with “Iced wine” and other unauthorized and fraudulent variations on the theme. Having a reliable means to verify that an “icewine” is really icewine made from frozen grapes seems prudent.

Per Armin Hermann’s new research, tracking oxygen isotopes could be that way. The idea is clever and conceptually simple. When grapes freeze, water partitions unequally between the part that turns to ice and the part that remains liquid. That’s the point of icewine: more water freezes, leaving sugars and other dissolved molecules concentrated in the syrupy liquid that remains. The naturally occurring isotope 18O, present in the water, will also distribute into the frozen and the unfrozen parts unequally. Since the frozen ice is more or less excluded from what ends up in a bottle of true icewine, then, icewines will contain a characteristic amount of 18O. All we need to do is determine — theoretically, using mathematical equations, and empirically, by measuring a bunch of icewines — what the “icewine” versus the “not icewine” 18O ranges are. Simple, elegant, and probably effective.

The plots of 18O measurements Hermann created show what looks like reasonably convincing separation between the ice- and non-icewine samples (understanding that judging how convincing is outside my expertise). BUT, there are two important caveats. First, the comparison was lab-frozen grape musts against the unfrozen originals. Again, it’s simple: “Frozen grapes, when pressed, will produce a must that is always depleted in 18O relative to its marc and also to their unfrozen counterparts.” The study didn’t include creating a database of icewine samples from various regions to establish reasonable 18O ranges. That’s solvable in theory, though the success of the whole method still depends on finding good, clear separation between real live ice and non-icewines.

Second, the method provides no way of determining how the wine was frozen. The 18O-depleted wine could have just as easily been frozen after harvest, in the winery, illegally. So, no matter how successful that empirical database is, the method won’t perfectly solve the how-do-we-detect-fakery problem. It is, as Hermann notes, an “additional” means giving a “strong indication” of authenticity. I wonder: is there a detectable chemical difference between the kind of slow freezing that would happen naturally on a grapevine in a cold Ontario winter and fast winery cryofreezing? Until then, looking for the Canadian VQA mark on the bottle — and avoiding anything labeled “iced wine” — remains the safest option, North American privilege notwithstanding.