Fermented Grape

how wine is produced

Debunking the world of wine

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Demystifying the world of wine

Wild yeasts in wine fermentation - Blast from the past, fad or future?

Saccharomyces cerevisiae yeast

It seems Fermented Grape is in full oenology mode. The science of wine making is fascinating especially as some maverick winemakers are choosing to make life more difficult and embrace nature. Risky, yes....but with risk there comes reward with fantastic wines.

Yeasts, single-celled microorganisms classified as members of the fungus kingdom, are a vital component in the production of wine. Without them alcohol would not be produced. The question for the wine industry in recent years has been whether the move by some wineries to use wild yeasts, a throw back to the past and origins of wine despite the associated challenges, is crazy or the way forward?

In winemaking, one of the most important characteristics of yeast is its ability to completely ferment all the sugar in grape juice and put up with high levels of alcohol. Without good alcohol in a wine it will not have the right body, flavours and aromas.

The fermentation process in wine production

First the science bit. Wine is produced during a biochemical process called alcoholic fermentation where yeast uses sugar to produce alcohol and carbon dioxide. A process well illustrated during the latter part of the 2011 French language movie starring Niels Aretrup. Excessive build up of carbon dioxide causes the premature death of the vineyard owner when the ventilation system is turned off by the vineyard manager! Super film by the way if you're a wine lover.

During maceration the grapes (skins plus seeds)  soak in the grape juice (the must) either prior to fermentation or during fermentation. In some wines the stems of the grapes are also included, in some cases not, a process called de-stemming. The Yeast does its stuff on the sugar during fermentation and after the process is finished they die and these dead yeast cells together with the other solids left in the fermentation tank are called lees. Lees can either be retained or removed from the fermented grape juice by methods called racking or fining or they may remain in the wine (so called non-fined wine). If the lees remain they will break down and release chemical compounds that interact with the fermented wine which can be used by the wine maker to create additional aromas and flavours.

If the lees are left to float down to the bottom of the container they coalesce, and assuming they aren't removed, wine makers need to stir to keep the lees mixed in with the aging wine. This is a process called Battonage (or Bâtonnage), a French term that ensures that all the wine liquid comes into contact with the lees, maximising the impact on it. This is traditionally carried out using a stick called a dodine or by putting the barrels on roller supports and turning the barrels. It promotes the death of the yeasts , which has the effect of giving more body and promoting the development of complex aromas in the wine. The baton is placed in the top opening of a barrel (bung hole) and gentle rotated within the barrel to stir the wine.

Yeasts - wild, inoculated and feral

Yeasts become evident in the must in a variety of ways, each one causing the wine to have different characteristics.  They can be inoculated in with cultured yeast cells using commercially produced products. Alternatively, winemakers can rely on wild yeasts.  The former has only been in use in more recent times.

Wild yeasts or sometimes called natural yeasts are wild in that they naturally live in the environment where the grapes are grown in the air, on vegetation or on equipment and can be quite specific to a particular location (indigenous yeasts).  However, there is no such thing as artificial yeast as all yeasts are natural and not synthetic. Any wild yeast species can end up in the must whether it is wanted by the winemaker or not and start to turn wine juice into alcohol during the fermentation process. Wine making is therefore made from fermentation using either wild or inoculated yeast.

Generally speaking, wild or indigenous yeasts have a low resistance to alcohol and when the alcohol reaches a certain level it can cause stuck fermentation. This causes a real headache for a wine producer - flabby low alcohol wines. Wild yeasts also exist on grapes and vines in much smaller numbers than inoculated yeast and it can take longer for wild yeast to multiply (up to a week in larger batches) leaving the grapes vulnerable to infection from bacteria and other organisms as well as oxidation. Grapes picked with a low acidity or pH naturally inhibit spoilage caused by other organisms during the lag phase it takes for spontaneous fermentation to start.

Feral yeast is a yeast that exists specifically in the winery on equipment or on barrels and its origin is often unknown. It could be wild yeast that blew in from outside or came in on winemakers cars, bodies or clothing. 

Born to be wild? 

Winemakers either love or loathe wild yeast fermentation. The big problem is that unlike inoculated yeasts, wild varieties can be unpredictable. Inoculated yeasts are much more reliable. For thousands of years wine was fermented using wild yeasts found naturally in the vineyard but nowadays most wineries inoculate in order to produce a consistent end product, barrel after barrel and year after year. There are thousands of different types of wild yeast but unfortunately many do not make good wine. Wild yeasts themselves can be broken down into two categories: wine yeast and spoilage yeast - the latter definitely aren't good for wine production.

Specific cultured yeast strains might be able to produce certain characteristics such a particular aroma or have an ability to ferment in certain temperatures. Others can produce sediment that settles quickly in the tank. 

The type of grape fermented will determine the strain of yeast chosen but the species of yeast considered most desirable for total alcoholic fermentation is Saccharomyces cerevisiae.

Major characteristics for an ideal yeast for wine making:

  • Fermentation speed
  • Alcohol tolerance
  • So2 tolerance
  • Cold tolerance : fermentation below 14ᵒc
  • Low foaming activity
  • Efficient conversion of sugar into alcohol
  • Production of desirable metabolites
  • Low production of undesirable metabolites: Such as acetaldehyde, acetic acid, sulphur dioxide and hydrogen sulphide
  • Resistance to “Killer” yeasts
  • Flocculation: An ideal yeast strain should flocculate at the end of the fermentation, leaving the wine clear and requiring less rigorous filtration

When grapes are harvested they are covered with lots of biological organisms, including bacteria and fungi as well as wild yeasts and winemakers use sulfur dioxide (SO2) kill wild yeasts and inhibit the growth of spoilage organisms. When inoculated yeasts are used the the dose is large enough to start fermentation quickly and for that strain to dominate if other wild strains are present. If rain fell just before harvest, wild yeasts may be washed off by the water and levels will be well down, insufficient to cause fermentation without further intervention. The moisture and the lower levels of yeast can cause bacteria to multiply in the must  or it can mean no Saccharomyces cerevisiae in the must at all. 

During the lag phase before fermentation starts, the must is vulnerable to bacterial growth and VA (volatile acidity) from acetobacter and lactobacillus. These bacteria can turn the previous wine into vinegar and produce terrible aromas such as rotten eggs.

When making wine with wild yeast, no Sulfur is added to the must and a process called spontaneous fermentation is allowed. The wild yeast just does its own thing at its own pace.

Some wineries have been fermenting on wild yeast for many, many years with successful results. For other winemakers spontaneous fermentation is a trendy new approach, a little on the edge, almost a gamble in the quest for better wines. Wild yeasts can help the grapes to produce specific chemical compounds e.g. esters that you just can't get with commercial products.

Because wild yeasts often take longer to work it allows more skin contact time on grapes potentially giving more body, complexity and colour to the finished wine. Wild yeasts can often impart unusual aromas and flavours they can help product distinctive, interesting wines. No two batches of spontaneous fermentation taste the same, even when grapes are from the same vineyard, fermented together in the same room.

The result can be a wonderful wine with fruit, amazing aroma and flavour, and with good alcohol. Though it is often much more of a gamble than using inoculation, for some the end result if worth the risk and this is the main reason why spontaneous fermentation is used in winemaking. Some winemakers are adamant that wild yeast is the only way as cultured yeasts produce boring, standardised wines with no character.  

There is often a half way house though. Winemakers allow spontaneous fermentation to begin using wild yeasts and take regular readings of the amount of sugar or specific gravity of the must, to determine the current alcohol. After alcohol has reached a certain threshold they may sometimes choose to inoculate with commercial S. cerevisiae to ensure complete fermentation. This achieves the desired quality but still allows the complexity of wild yeast.

Old world winemakers use a process called Pied de Cuve to ensure that fermentation begins. A small amount of their grapes are picked a week before the harvest and water may be added to overcome excess acid. The must is stirred to stimulate the wild yeast and start spontaenous fermentation. After several days, these grapes will be nicely fermenting and this starter culture is used to inoculate the harvested grapes when they come in after picking some days later. So instead of inoculating with bought in yeasts, inoculation occurs with the indigenous yeasts.

New Zealand wine producer, Pyramid Valley Vineyards, say that "All of our fermenters are 1,000 litres or less, which allows us to be very close to the wine in a physical sense. This allows us to hand and foot plunge and allows us to listen to the health of each ferment before we intervene. We never use commercial yeast for fermentation. We culture our own yeast through starter cultures, developed in each vineyard we source fruit from. This is a  technique that Mike Weersing developed to ensure that each of our wines talks entirely about where it is from without compromise from commercial yeast."

For those keen on their organic, biodynamic wines with mininal intervention in the vineyard or winery, wild yeast fermentation may be a game of chance, but a valid one for wines with a difference.

"Is there a better way to talk about wine?" by Bianca Bosker

An interesting article by Bianca Bosker from The New Yorker and "bullshit" wine speak by the critics. Just gone and bought her book on Kindle store called Cork Dork, looks a good read.

Is There a Better Way to Talk About Wine?

By Bianca Bosker, July 29, 2015

When the wine critic James Suckling described a Château Haut-Brion in the pages of Wine Spectator in 1992, he needed just a single phrase to sum up the taste: “Big and meaty, with lots of fruit and full tannins, but featuring a sweetness and silkiness on the finish.” At the time, the field of wine criticism was gaining momentum—the magazine’s circulation that year surpassed a hundred thousand—and written tasting notes were moving beyond encyclopedic reference books aimed at wealthy men_._ When Suckling sampled the same Haut-Brion again—a bottle from the acclaimed 1989 vintage—in 2009, his description of the wine’s flavor carried on for seven sentences, evoking cigarettes, pastries, and saunas in his promise of “perfumed aromas of subtle milk chocolate, cedar, and sweet tobacco.”

It’s possible that the renowned Bordeaux wine had evolved during the intervening decade and a half, but, then again, so had the tasting note. In recent years, flowery, elaborate flavor descriptions have become commonplace in the wine world and beyond, regularly speaking to us from wrappers of artisan chocolate bars, menus of craft beers, and display cases of gourmet cheese. Stumptown Coffee advertises Rwandan beans redolent of “crisp melon and subtle powdered cocoa.” Silver Haze, an award-winning strain of marijuana, gives off an “intense, mineral nose.” Wine stores, sommeliers, critics, and importers share tweet-length assessments of rare vintages via online oenophile apps.

But, as extravagant tasting notes have become de rigeur in the marketing world, they’ve also arguably lost their practical function as consumer guides. A 2007 study published in the Journal of Wine Economics gave amateur drinkers two different glasses of Bordeaux along with a professional critic’s tasting notes, and asked them to match each review with the correct glass. An “unctuous” 2000 Clos du Marquis supposedly evoked “crème de cassis, vanilla, and cherry”; the 2000 Château Talbot had flavors of “licorice, herb, earth, and leather.” The subjects performed no better at identifying each wine than if they’d guessed at random. Read any wine review or bottle label today and you will likely empathize with their confusion. Swallowing a substance that tastes of “strawberry bubble gum with tar” sounds like punishment, yet somehow Suckling extols this Montalcino as “delicious”; a drink with flavors of “graphite” mixed with “pâte de fruit, hoisin sauce, warm ganache, and well-roasted applewood” calls to mind a dinner party gone wrong, not a Wine Spectator Pick of the Year. And how can one know whether a bottle that the bimonthly newsletter Wine Advocate dubbed “liquefied Viagra” pairs better with salmon or pork?

Frustrated with the state of modern winespeak, some academics, sommeliers, and critics are attempting to rein in tasting notes and develop new idioms that convey quality more concretely**.** A group of researchers known as the American Association of Wine Economists has waged a nearly decade-long crusade against overwrought and unreliable flavor descriptions. In 2007, the association’s Journal of Wine Economics ran an analysis of wine critics which concluded that the industry was, in no uncertain terms, “intrinsically bullshit-prone.” “We, the wine-drinking public, are happy to read their evaluations, because we are largely ignorant of the quality of wines,” the study’s author, the Princeton economist Richard Quandt, wrote. (He and the president of the Wine Economists, Orley Ashenfelter, shun tasting notes in their own wine club.) Another contributor, Jordi Ballester, is a researcher at the Center for Taste and Feeding Behavior, in Dijon, France, who’s spent his career weeding out wine bullshit—or what he more politely terms “fuzzy concepts.”

In Ballester’s experience, the virtually limitless diversity of wines—paired with the “elevated language” that plagues élite hobbies—make the field especially susceptible. His past research has examined whether intrinsic wine quality exists, how experts deem a bottle worth aging, and what logic, if any, governs tasting notes. The buzzword “minerality” is his latest “victim,” Ballester told me, and was the subject of a paper shared at the Wine Economists’ annual conference, in May. The term, which has become popular in the past decade, is often attached to higher-acid white wines like those of Chablis, a region of Burgundy famous for its limestone soil. Last fall, Ballester dispatched a doctoral candidate to ask Chablis’s winemakers and consumers what “minerality” calls to mind. (According to a 2009 paper presented to the Geological Society of America, grape vines do absorb inorganic nutrients from the land, but the notion of granite or schist seasoning wine in any detectable way is “scientifically untenable.”) The researcher collected hundreds of answers, from “salty” and “gunflint” to “chalky” and “mineral water.” “We never found a consensual definition of minerality,” Ballester told me. “So how can we communicate like this?”

Like “minerality,” the very idea of describing a wine’s flavor is a relatively new phenomenon. The ancient Greeks and Romans, the Western world’s original wine snobs, generally used broad and imprecise descriptions for their vintages, preferring to pass judgment rather than dwell on aromas. In “The Odes,” Horace wrote that wines from the Sabine grape, apparently the ancients’ Yellowtail, are “humbly cheap.” The Falernian, from Southern Italy, by contrast, was “strong” and “powerful”; Pliny the Elder wrote that “there is now no wine known that ranks higher.” (Evidently no stranger to hangovers, Pliny elsewhere warned that wines from Pompeii are “productive of headache, which often lasts so long as the sixth hour of the next day.”) In the centuries that followed, oenophiles continued to focus on critiquing and praising wines rather than dissecting their flavors. Samuel Pepys, a high-ranking Admiralty officer whose diary offers a rare record of seventeenth-century drinking culture, reviewed an Haut-Brion in a meagre half sentence that would dismay the Wine Spectator crowd: “A good and most particular taste that I never met with.” By the late nineteenth century, better winemaking methods had helped to raise wine’s status as an art form, and oenophiles were beginning to evolve into the loquacious species they are today. From the nineteen-seventies onward, the variety and affordability of wines fed a market for experts who could help drinkers to navigate between bottles. Three centuries after Pepys, Robert Parker, the celebrity critic who introduced a hundred-point scale in the Wine Advocate, raved of an Haut-Brion’s “sweet nose of creosote, asphalt, blueberries, black currants, and jammy raspberries,” adding, “This is profound!”

The figure most responsible for the emergence of the modern sommelier lexicon was not a swish-and-spit celebrity like Parker but a professor of viticulture and enology at the University of California at Davis named Ann Noble. In 1984, Noble, drawing upon the work of other sensory scientists at Davis, published the Wine Aroma Wheel, a circular chart of six dozen descriptors that could be used to describe wine by smell. Like Ballester, Noble, who is now a professor emeritus at Davis, told me that she was motivated, in part, by a desire to eradicate fuzzy concepts. She organized her chart into broad categories such as “spicy” (cloves, black pepper, and licorice) or “fruity” (strawberry, lemon, and melon), and in an accompanying user guide argued against terms that were “hedonic” or “the result of an integrated or judgmental response,” and in favor of “specific and analytical” ones. (Minerality didn’t make the cut.) For the first time, winemakers, critics, and consumers had a common lexicon to draw upon. One researcher at the Burgundy School of Business told me that the Aroma Wheel is considered “the Ten Commandments” of the wine world. (Calvin Trillin wrote about Noble, and the challenges of telling a red wine from a white, in 2002.)

But even with a standardized vocabulary, the flavor of wine—like any form of taste—is dependent in large part upon the biases and predilections of the person doing the tasting. Scholars who have studied the language of wine critics have shown how cultural ideals of masculinity, class, and even physical fitness have influenced flavor descriptions in past decades. (Who knew that a wine could be “broad-shouldered” or “sinewy”?) Today, in a farm-to-table food culture that worships at the altar of the artisan, hundred-point favorites are often presented as farmers’ markets in a bottle, with comparisons to “wild strawberry” or “wet hay” conveying a rustic gastronomic ideal. Where Noble’s list included suburban-pantry references like “canned green beans,” a recent Wine Spectator review for a Châteauneuf-du-Pape mentioned “baker’s chocolate, espresso, bay, licorice root, black currant preserves, and steeped fig.” It seems possible that what we “taste” in a fine wine isn’t so much its flavor as the qualities of good taste that we hope it will impart to us.

Bias sneaks in in subtler ways as well. A doctoral candidate at Harvard University’s Social Cognitive and Affective Neuroscience Lab recently uncovered “euphemistic signs of quality” in the winemakers’ notes that appear on bottle labels, with words like “nutty” and “refreshing” corresponding to wines that had received low ratings from critics and rarified terms like “brioche” and “cru” corresponding to high-scoring ones. Similarly, research presented at the American Association of Wine Economists conference in 2013 showed that reviewers reserve florid prose for expensive bottles and use simpler, more pedestrian language to describe Two Buck Chucks. In other words, the fancier a wine appears—or is meant to be—the fancier the words critics conjure to describe it. It’s easy to see how this tendency helps to reinforce the status of high-end vineyards: spending hundreds of dollars on a vintage with aromas of “leather,” “eucalyptus,” and “Japanese maple” sounds more justifiable than splurging on one with flavors of “canned olives with black pepper.” (Maria Konnikova has written for this site about the psychology of wine tasting.)

So how best to confront the obfuscating nature of modern winespeak? One option is to think of flavor in terms of chemistry rather than gastronomy. In April, the Guild of Sommeliers, a nonprofit association of fine-wine specialists, created a cheat sheet encouraging wine professionals to name the chemical compounds that are responsible for the odors in a glass. When discussing wines with other experts, the guild suggests identifying hints of raspberry and strawberry as “esters,” peppercorn or rosemary aromas as “rotundones,” and gooseberry or grapefruit notes as “thiols.” A Sauvignon Blanc with notes of, say, green pepper might more accurately be said to smell of pyrazines, traces of which are present both in the vegetable and in grapes. This approach doubles down on the rigor of Ann Noble’s aromatic taxonomy, tethering smell more firmly to science. Geoff Kruth, a master sommelier and the chief operating officer of the Guild of Sommeliers, told me that the goal is to “make a connection between understanding the intrinsic, objective factors that are in a wine and the ways to describe them.”

To Matt Kramer, a Wine Spectator columnist and the author of a new manifesto called “True Taste,” the very notion of objectivity is a fuzzy concept—“a great myth of modern wine tasting,” he writes, and one that exists in “such a confined fashion … as to render it more a laboratory reality than a real-life one.” While the Guild’s chemical vocabulary indulges the Fitbit generation’s reverence for data, scientific rhetoric, and quantifiable hedonism, Kramer instead seeks to recapture the critical experience of drinking wine. In his view, only six words are necessary to evaluate a bottle’s essential attributes: “harmony,” “texture,” “layers,” “finesse,” “surprise,” and “nuance.” Australian Cabernets are “graceful wines of elegance and finesse.” A Sauvignon Blanc’s “denser textures” feature aromas of fig and melon. In contrast to the modern convention of meticulously describing the subtleties of flavor, Kramer prioritizes conveying judgments of quality—the critic’s most fundamental task. (He includes a seventh term, “insight,” to refer to the job of the wine critic.)

Yet there is something a bit dreary about Kramer’s call for such unvarnished expressions of judgment—something as inaccessible, in its way, as references to thiols or pyrazines. If such approaches can help to bring much-needed precision to wine reviews, they also seem less likely to stimulate a drinker’s curiosity or imagination in the way that a fruit salad of flavor descriptions might. At a recent dinner party in Manhattan, I heard one guest, a sommelier, liken a Barolo he’d recently tasted to a “male ballet dancer.” I laughed the comment off at the time—yet another example of oenophile pretensions—but a few days later I found myself scanning the shelves of my local wine store, wondering what a Baryshnikov in a glass might taste like. Those of us who enjoy wine apparently appreciate a little mystery along with our fermented grape juice. As Geoff Kruth, the master sommelier, told me, “At the end of the day, we’re selling poetry.”

Bianca Bosker is the author of “Cork Dork," a book about wine, obsession, and the science of taste out now from Penguin Books.

Secret wine note on 2600 year old Hebrew tablet

For 2,600 years, the message was hidden on a stone tablet. It had been missed by the best Hebrew scholars and by thousands of museum visitors over decades. But using the latest imaging technology, scientists have revealed a rare message from biblical Judea saying "Send us wine".

A team of Israeli scientists has found that one particular shard of pottery, held in a museum for 50 years had been hiding a message. Using full spectrum light imaging techniques they revealed the hidden message, between a soldier in a desert fortress and his quartermaster.

Although the beginning of the message discussing supplies for the camp had been visible, new words have been added and an extra passage discovered on the reverse side. This new text complains that someone called Ge’alyahu had taken some sparkling wine and makes the request it is replenished: “If there is any wine, send”.

Barak Sober, from Tel Aviv University, was one of the scientists involved in the find, which is reported in the journal PLoS One. “It was remarkable to discover completely new inscriptions,” he said. “This was lying in a museum for half a century and many Hebrew scholars were examining it over the years and nobody even considered the reverse side as something that was interesting or important.”

One of the more intriguing aspects was the fact that the soldier involved begins the letter, we now know, by referring to the quartermaster as “beloved”. Dr Sober said: “It’s . . . a really unique choice of words. Maybe they were colleagues, good friends. I don’t figure they were lovers.” He said that, as fascinating as it was to ponder the mysterious relationship between the soldiers, or the alcoholic tendencies of Ge’alyahu, the proof of principle was more important than the specific find itself.

“There are very few inscriptions from that time. Maybe 300,” he added. Unlike in Egypt, the climate was humid at the time so papyruses did not survive. “There is very little evidence of written words in Hebrew at that time. So each find expands the vocabulary and grammar.” This can be useful in analysing and dating biblical passages.

Even more generally, he said that the technique showed archaeologists should be more careful and think about applying the same technique, which used a digital camera to divide the colour spectrum into dozens of bands, rather than just the standard red, green and blue.

Mr Sober said: “The really sad thing is to think how many inscriptions have been overlooked because nobody saw what was there. If you go on excavations you see a huge amount of pottery being thrown away. Maybe some of it was written on.”