- Wines that age well make up only a tiny fraction of overall production, but get a great deal of attention from wine lovers. Do we know how this process works?
- Research in the last half-century has increasingly focused on the role of complex phenolic polymers in preserving wines against damaging forms of oxidation.
- Acidity and pH are also critical, particularly in white wines that lack red wine phenolics.
- Predicting whether a wine will "hold together" for 20 years is easier than predicting how it will smell and taste.
One of wine's most magical properties is its ability, unique among foodstuffs, to not only survive but improve with long-term aging. A good cheese may benefit from a year or two of affinage,
but only after a decade or two (or three or four) does the full wonder of a fine wine emerge--if, that is, it hasn't completely fallen apart in the meantime.
The respect paid to wine's ageability is one of the first nuggets of knowledge new wine drinkers encounter, often leading to the utterly incorrect notion that all
wines can and are supposed to age. In fact, only a tiny percentage of the world's wines are built for longevity, and only some of those candidate wines in fact grow old gracefully. The negligible volume of these much-prized wines helps explain why they aren't the focus of much research.
So if some wines age well, and most wines don't, do we know why? Can we quantify the wine chemistry of the sprinters and the distance runners? If they wanted to, could winemakers just tweak a couple techniques and make all their products suitable for laying down for the grandchildren? Can researchers or winemakers accurately predict the trajectory of a particular wine the day it goes into bottle--or is that kind of prognostication best left to the marketing department?
This investigation into the whys and wherefores of aging will be divided into two columns: this time a review of the state of our scientific knowledge, according to some prominent researchers, and next month a survey from the vantage point of veteran winemakers trying to parse out one vintage after another. Trending toward tannins
Over the sweep of history, many factors have been cited as keys to the ability of some wines to age, and most of these continue to have some currency, at least in the popular/consumer discourse about ageability. Sugar must have something to do with the amazing life expectancy of sweet-style German Rieslings; and the trajectories of those same wines also suggest a life-affirming role for acidity. High alcohol, especially in the form of fortified wines, has a history as a means to ensure stability in wines long enough for their hidden charms to surface.
But for the past several decades, researchers have increasingly focused on the preservative powers of phenolic compounds, particularly tannins and anthocyanins. One of the contributions of French enologist Emile Peynaud in the mid-20th century was to argue for the centrality of tannins, rather than acid, in wine aging, with the corollary observation that the combination of high tannin content and high acidity made for hard wines that might live forever but never become drinkable.
The key players on the phenolic team are the complex polymeric combinations of anthocyanins and tannins that develop--maybe--in the first few years of wine aging and play a critical anti-oxidant role for the years after that. Phenolics researcher Andy Waterhouse of the University of California, Davis, calls these compounds "a sink for oxygen," giving color, aromas and flavors an extended lease on life. It's not so much that pigmented polymers prevent oxidation; rather, they promote and are in part a result of "good" oxidation, a particular, beneficial form of oxidative reaction. This is why the technique of intentional micro-oxygenation speeds up the process of maturation, encouraging those friendly phenols, rather than damaging the wine with "bad" oxidative reactions.
Besides serving as anti-oxidants, the polymerized tannins are behind the evolution of mouthfeel, from firmer and more astringent to softer and rounder. Even though long-chain tannins are generally more astringent than shorter forms--the way gravel is scratchier than sand--the polymeric phenols somehow find a way to become less rude. We don't yet know exactly how this happens.
Nothing in wine is forever, and so the phenolic guardians can only hold off the inevitable decomposition and breakdown so long.
Color goes from red to brick to brown (or straw to amber), fruit flavors go away, mouthfeel wanes into nothingness, and eventually wine is reduced to little more than acidity. But phenolic content does play a key role in distinguishing long-lived vintages from those that quickly fade, and in separating mass-market, drink-it-tonight wines from those with aging potential.
Since other factors clearly come into play to affect the aging curve, there is no magic number for correlating phenolic content and optimum cellaring. Wine microbiologist Ken Fugelsang of California State University, Fresno, says, "People have been trying to reduce ageability to a number for 20 years, but since that is a dynamic system, that's not achievable."
But as a rule of thumb, both Waterhouse and Jim Kennedy, a tannin specialist at Oregon State, suggest that a total phenolics measurement of 2.5 grams per liter or higher likely would put a red wine in the ballpark as a prospective ager. Kennedy also notes that with just a pinch of residual sugar to mask astringency, wines with even higher total phenolics measurements can be quite drinkable. Acid, pH and alcohol
Even the fans of phenolics acknowledge that acidity and its kissing cousin, pH, are also important factors. Acid-catalyzed reactions march on alongside oxygen-related reactions, affecting flavor and aroma compounds. A wine's pH sets the framework in which all of these dynamics unfold, and its acidity ha s everything to do with how it tastes at any stage of development.
Leo McCloskey of Enologix, a Santa Rosa, Calif., consulting firm that advises high-end clients through use of an extensive wine analysis database, insists that pH is critical; the seemingly small difference between a pH of 3.6 and a pH of 3.7 makes, he says, a tenfold difference in ageability. And while Peynaud may have emphasized tannins over acidity as the path to longevity, his idea of a moderate level of acidity might seem downright high compared to what's found in many of today's big California reds.
And then there's alcohol--and these days, lots of it. Everyone I spoke with agrees that the different chemistry of high-alcohol wines means they will age differently from the old familiar 12.5%-in-a-good-year benchmark Bordeaux wines of yesteryear. But different isn't necessarily bad. Kennedy says it's possible to create wines with a new kind of balance--more alcohol, more phenolic extract, lower acidity, higher pH--and with the help of a fractional percentage of sweetness have them be appealing both now and later on.
"The Bordeaux standard that we're used to," Waterhouse says, "had moderate alcohol and low pH. What the current ones will taste like we can only speculate about, but we can guarantee they will be different. If we hold to that historical standard, they won't be as 'good'--but a lot of people may enjoy them." Throw in factors such as climate change, (riper grapes) and changes in closures (screwcaps that alter the oxidation rate), and it's clear that the sensory profile for long-lived wines is a moving target. Aromatic and flavor changes
What we like about old wines is not just their age; it's also the mutation of how they smell and taste. Favored descriptors for well-aged wines include just about everything but fruit; many of them--like cooked corn--don't even sound that great on paper. These new/old organoleptic dimensions are one reason not everybody craves these wines. But for those who do, simple longevity isn't the whole story: great wines have to get better, too, and our friends the phenols can't do that part of the job.
A wine can hold together perfectly well for many years and still be boring. What makes the difference, says flavor chemist Sue Ebeler of UC Davis, is hydrolysis: the capacity of ethanol (and acidity) to break down compounds and release volatiles, making new compounds in the process. Besides needing alcohol as the active agent, wines need to have the right precursors available for those nifty aromatics. Analyzing and predicting this part of the aging process is a lot tougher than measuring total phenolics.
Which gets us to white wines, some of which age remarkably well without benefit of tannins or anthocyanins. Whites pursue a very different chemical logic from what happens in red wines, leading to very different sensory results.
When I asked Jim Kennedy what makes white wines age, his first response was, "Beats me--I'm kind of a red wine guy." It turned out, of course, that he and the rest of my consultants knew a big part of the answer here really is acidity, a hallmark of both German Rieslings and great white Burgundies. Without phenolics to scavenge oxygen, winemakers have to limit how much of it gets into the wine in the first place. To buy time for the emergence of old white wine aromatics over many years--Riesling's famous petrol characteristic, for example--winemakers have to worry about acidity, pH, and the control of temperature and oxygen uptake--plus have grapes with a lot of volatile and pre-volatile stuffing in the first place. Predictions, anyone?
In summary, we know a lot about the processes and chemical composition that affect aging. We know what phenols do, and we can catalog many of the precursors and aromatic volatiles that make up an old wine's bouquet. We also know the importance of storage conditions, particularly temperature, and the whole discussion presupposes that the wines under consideration are microbially stable, not sacrificing their future to a Brett bloom or some other unfortunate event.
Given all that, and given all the grad students and lab equipment imaginable, can wine scientists predict how and how well a wine will age on the day it's bottled?
Andy Waterhouse thinks that if we know about a wine's tannins and acidity, we can predict whether it will stand up to aging. Jim Kennedy says he knows we can distinguish between Two Buck Chuck and Screaming Eagle in the lab, and "likes to think" we could predict how a wine will fare over the years.
On the other hand, Sue Ebeler says we aren't at the point where we can predict tomorrow's sensory profiles from today's chemical composition--there are too many complex interactions that affect perceptions. And while Ken Fugelsang says that maybe he could make a projection about a wine "plus or minus five years," he also thinks we're a long way from the finish line in understanding how all this works.
Can we foresee how long a wine will live, or at least which ones will live for a long time? Probably. Can we prophesy what the survivors will taste and smell like? Probably not.
Next time: what do the winemakers think? When a new vintage goes out of the cellar, how confident are they about how it will end up? Tim Patterson writes about wine and makes his own in Berkeley, Calif. Years of experience as a journalist, combined with a contrarian streak, make him interested in getting to the bottom of wine stories, casting a critical eye on conventional wisdom in the process. He may be contacted through email@example.com.