The New York Academy of Sciences Magazine -- The Science of Red Wine

7/27/2019 The New York Academy of Sciences Magazine -- The Science of Red Wine

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the Scienceof RedWine

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Update MagazineMay/June 2007

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Treasurer : Counsel: Secretary :MICHAEL SCHMERTZLER VICTORIA BJORKLUND [ex ofcio] LARRY SMITH [ex ofcio] Governors:KAREN E. BURKE VIRGINIA W. CORNISH BRIAN FERGUSONMARIA C. FREIRE JAY FURMAN BRIAN GREENEWILLIAM A. HASELTINE STEVE HOCHBERG MORTON HYMANMAREN IMHOFF MADELEINE JACOBS ABRAHAM LACKMANBRUCE MCEWEN JOHN F. NIBLACK ERIC A. ROSEJEFFREY D. SACHS FRANK WILCZEK DEBORAH WILEY Honorary Life Governors :WILLIAM T. GOLDEN JOSHUA LEDERBERG TORSTEN N. WIESEL Presidents CouncilRICHARD AXEL, Nobel Laureate & University Professor, Columbia Univ.; Investigator, HHMILEE BABISS, Vice President, Pre-Clinical Research & Development, Hoffmann La RocheDAVID BALTIMORE, Nobel Laureate & former President, CaltechETIENNE-EMILE BAULIEU, former President, French Academy of SciencesELEANOR BAUM, Dean, School of Engineering, The Cooper Union for the Advancement of Science and ArtPAUL BERG, Nobel Laureate & Professor Emeritus, Dept. of Biochemistry, Stanford Univ.LEN BLAVATNIK, Chairman, Access IndustriesGNTER BLOBEL, Nobel Laureate & Director, Laboratory for Cell Biology, Rockefeller Univ.CHRISTIAN BRECHOT, Director General, INSERM, FranceSYDNEY BRENNER, Nobel Laureate & Distinguished Prof., Salk Inst.MICHAEL S. BROWN, Nobel Laureate & Prof. of Molecular Genetics, Univ. of Texas Southwestern Medical CenterLINDA BUCK, Nobel Laureate & Investigator for HHMI, member of the Fred Hutchinson Cancer Research CenterKAREN E. BURKE, Dermatologist & Research ScientistTHOMAS R. CECH, Nobel Laureate & President, HHMIGORDON CONWAY, Chief Science Advisor, UK Department for International DevelopmentPETER DOHERTY, Nobel Laureate & Researcher, St. Jude Childrens Research Hospital, Memphis, TN; University of MelbourneFRANK L. DOUGLAS, Executive-in-Residence, MIT Sloan School of Management; former Executive Vice President, AventisPETER FARINA, Senior Vice President, Development, Boehringer Ingelheim Pharmaceuticals, Inc.EDMOND H. FISCHER, Nobel Laureate & Professor Emeritus, Department of Biochemistry, University of WashingtonRICHARD N. FOSTER, Managing Partner, Foster Health PartnersCLAIRE M. FRASER-LIGGETT, former President & Director, The Inst. for Genomic Research (TIGR)

ALAN J. FRIEDMAN, former Director, New York Hall of ScienceJEAN-PIERRE GARNIER, Chief Executive Ofcer, GlaxoSmithKline, UKCOLIN GODDARD, Chief Executive Ofcer, OSI PharmaceuticalsWILLIAM T. GOLDEN, Honorary Life Governor; Honorary Life Member, New York Academy of Sciences;

Chairman Emeritus, American Museum of Natural HistoryJOSEPH GOLDSTEIN, Nobel Laureate & Chairman, Molecular Genetics, Univ. of Texas Southwestern Medical CenterPAUL GREENGARD, Nobel Laureate & Prof. of Molecular & Cellular Neuroscience, Rockefeller Univ.PETER GRUSS, President, Max Planck Gesellschaft, GermanyWILLIAM A. HASELTINE, President, The Haseltine Foundation for Medical Sciences and the Arts;

Chairman, Haseltine Global Health, LLCERIC KANDEL, Nobel Laureate & Prof., Physiology & Cell Biology, Columbia Univ.KIYOSHI KUROKAWA, Science Advisor to the Prime Minister of Japan; Adjunct Professor, RCAST, The University of Tokyo;

Professor, Research Institute of Science and Technology, Tokai UniversityJOSHUA LEDERBERG, Nobel Laureate & Honorary Life Governor, New York Academy of Sciences;President Emeritus, Rockefeller Univ.

LEON LEDERMAN, Nobel Laureate & Pritzker Prof. of Science, Illinois Inst. of Tech.;Resident Scholar, Illinois Math & Science Academy

RODERICK MACKINNON, Nobel Laureate & John D. Rockefeller, Jr. Prof., Rockefeller Univ.; Investigator, HHMIJOEL S. MARCUS, Chief Executive Ofcer, Alexandria Real Estate Equities, Inc.GERALD J. MCDOUGALL, National Partner, Global Pharmaceutical & Health Sciences Practice, PricewaterhouseCoopers LLPRICHARD MENSCHEL, Senior Director, Goldman SachsRONAY MENSCHEL, Chairman of the Board, Phipps Houses; Board of Overseers, Weill Cornell Medical CollegeJEAN-MARC NEIMETZ, Vice President, Global Life Science Group, CapgeminiJOHN F. NIBLACK, former President, Pzer Global Research & DevelopmentPAUL NURSE, Nobel Laureate & President, Rockefeller Univ.ROBERT C. RICHARDSON, Nobel Laureate & Senior Vice Provost for Research, Floyd R. Newman Prof. of Physics, Cornell Univ.PETER RINGROSE, Chairman, Biotechnology & Biological Sciences Research Council, UK; former CSO, Bristol-Myers SquibbEDWARD F. ROVER, President, The Dana FoundationF. SHERWOOD ROWLAND, Nobel Laureate & Prof. of Chemistry & Earth Science, Univ. of California, IrvineBENGT SAMUELSSON, Nobel Laureate & Prof., Medical & Physiological Chem., Karolinska Inst.;

former Chairman, The Nobel FoundationCHARLES SANDERS, former President, GlaxoSmithKlineISMAIL SERAGELDIN, Librarian of Alexandria, Director of the Bibliotheca Alexandria, The Library of Alexandria, EgyptPHILLIP A. SHARP, Nobel Laureate & Director, The McGovern Inst., MIT Center for Cancer ResearchELLIOTT SIGAL, Chief Scientic Ofcer, Bristol-Myers SquibbMICHAEL SOHLMAN, Executive Director, The Nobel FoundationPAUL STOFFELS, Company Group Chairman, World Wide Research & Development, Pharmaceuticals Group, Johnson & JohnsonMARY ANN TIGHE, Chief Executive Ofcer, New York Tri-State Region, CB Richard EllisSHIRLEY TILGHMAN, President, Princeton Univ.HAROLD VARMUS, Nobel Laureate & President & CEO, Memorial Sloan-Kettering Cancer CenterHERBERT M. WACHTELL, Founding Partner, Wachtell Lipton Rosen & KatzFRANK WALSH, Executive Vice President, Discovery Research, WyethGERALD WEISSMANN, Prof. of Medicine, NY Univ. School of MedicineJOHN WHITEHEAD, former Chairman, Lower Manhattan Development Corp.; former Co-Chairman of Goldman SachsGEORGE WHITESIDES, Mallinckrodt Prof. of Chemistry, Harvard Univ.TORSTEN N. WIESEL, Nobel Laureate & Honorary Life Governor, New York Academy of Sciences;

Secretary General, Human Frontier Science Program Organization; President Emeritus, Rockefeller Univ.FRANK WILCZEK, Nobel Laureate & Herman Feshbach Professor of Physics, MITERNST-LUDWIG WINNACKER, Secretary General, European Research Council;

former President, Deutsche Forschungsgemeinschaft, GermanyGUANGZHAO ZHOU, former Chairman, Chinese Association of Science & Technology

On the cover:On the cover: Red Red WineRed Red Wine , an abstract, an abstractphotographic image of red wine by Kian Eriksenphotographic image of red wine by Kian Ean illustrator from Cape Town, South Africaan illustrator from Cape Town, South Afri


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TheThe ScienceScience ofof RedRed Wine Wine

By James KennedyFlavor, Texture, and Tannins

Wine can o their wits thewise beguile, Make the sage rolic, and

the serious smile. Homer, The Odyssey (Alexander Pope translation)


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Update May/June 2007 11

elebrated or centuries, redwine has extensive histori-cal, cultural, and economic

signifcance in the Western world. Wine

connoisseurs become enamored with themystique o a supple Burgundy or an ex-plosive Australian Shiraz. Tey expoundon the taste o black currants and leathercoexisting in the same wine.Te averagewine drinker, by contrast, may be contentto distinguish between dry and ruity.Yet it is unlikely that either consumer ully grasps how dynamic the chemical systemis that trans orms a simple ruit juice intoan ever-evolving synthesis o soil, sun, ox-idation, winemaker in uence, and age.

THE CHEMISTRY OF WINE

Wine is a complex liquid. Although wa-ter, ethanol, glycerol, and various organicacids comprise the major (nondescript)portion o wine, its distinct identity comesrom the aroma compounds (such as ter-penes, esters, and alcohols), polysaccha-rides and phenolics (such as anthocyaninsand tannins). Some aroma compoundsare present in the grapes rom which thewine is made, and some are synthesized asby-products o ermentation by the yeastthat turns the sugar in the grape must intoethanol. Still others are ormed only a er

wine has been aged and are the result o oxidation and acid-catalyzed reactions.Tis constant evolution o the di erentkinds o aroma compounds is one o themany subtle aspects o wine appreciation.

Polysaccharides are polymeric un er-mentable sugars that lend body and viscos-ity to a winewithout them, a wine mightseem thin or watery. Tese compoundsare ormed during ruit ripening when thegrape berry so ens. Te riper the grape, themore these components are ound in thefnal wine. Tis explains why wines rom

warm growing areas (Australia, the Cen-tral Valley in Cali ornia) o en have morebody than those rom cooler climates.

annins contribute to the color sta-bility, astringency, and bitterness o wine.Tis combination o actors is critically im-portant to the age-worthiness and textureo wine, and possibly has health benefts.With regard to texture, tannins can be apositive or negative in uence. Tis dual-ity is a core aspect o red wine qualitythe

right amount o the right type o tanninyields a blockbuster wine, whereas toomuch o the wrong type o tannin resultsin a wine lacking character and suppleness.

From a chemical and research standpoint,tannins are probably the most defningcomponent o the quality o red wine.

WHAT ARE TANNINS?

annins (sometimes re erred to as proan-thocyanidins or condensed tannins) area class o complex avonoids that are lo-calized in the grape skin and seed and areextracted into the wine during ermenta-tion. Flavonoids are ound in plantsandinclude several compound classes such asanthocyanins (responsible or the color inmany ruits and owers), catechins (the

healthy component o green teas), andavonoid-based tannins ( ound in blue-berries, apples, cranberries, bananas, andquinces). annins encompass a large mo-lecular weight range and interact strongly with most proteins. Tis interactive prop-erty is the unctional role o tannins in na-ture. For example, many developing ruitscontain large amounts o tannins, whichinteract strongly with salivary proteins.Any creature eating the ruit perceives it

as astringent; there ore, tannins are e ec-tive eeding deterrents. Tis same prop-erty explains why tannins are the com-ponent o red wine that makes the tastersmouth pucker, a distinctive characteristico red wine.

Although scientists understanding o the physiology o taste is incomplete, wedo know that tannins can be perceived asgood or bad. Wines with good tan-nins we o en describe as ripe, supple,

lush, velvety, or round, whereas awine with bad tannins we fnd unripe,hard, coarse, and bitter. Tis is muchlike how we describe the taste o ruit

(think o the experience o eating an un-derripe banana in contrast to one that isully ripened). Eating an underripe ruit isnot a pleasant experience or most people,yet with su cient time and ripeness, theruit emerges as a succulent and tasty mor-sel. Where did the tannin go? Troughthe complex biochemical process o ruitripening, the tannins, while still in theruit, have become inactivated by theproduction o sugars, oxidation, and thebreakdown o cell-wall material. Te ruitbecomes a delectable treat. In the caseo red wine, changes in the grape duringruit ripening yield wine with increasingly ripe tannins.

ASTRINGENCY AND TEXTURE

Te molecular structure o the di er-ent tannins is strongly correlated with itssensory property in wine: the lowest-mo-lecular-weight tannins can have a distinctbitterness associated with them, whereasthe larger-molecular-weight tannins are re-garded as purely astringent. Whether thesesensory properties are considered individu-ally or in combination, they are almost uni-

versally regarded as negative. Humans haveevolved in such a way that we fnd bitter-ness and astringency to be repulsive. How can this repugnant taste become somethingwe desire and prize in red wine?

annins become palatable in ruitbecause our ability to perceive tannins isin uenced by many things. Tis combinedperception o tannin in the presence o other components is described as textureor mouth eel in the wine world. In many ruits, organic acids are produced at thesame time as tannin and the combination

o high organic acid and tannin concen-trations yields a very astringent (and sour)experience. During ruit ripening, sugarsare produced, and our ability to perceiveastringency diminishes as the sweetnessincreases. Moreover, many ruits so enduring ruit ripening, due to cell-wallbreakdown. Te breakdown o cell-wallmaterial produces soluble polysaccharideswhich interact with tannins, once againreducing their astringent properties.

C

Wines with good tanninsWines with good tanninswe often describe as ripe,we often describe as ripe,supple, lush, velvety,supple, lush, velvety,

or round, whereas a wineor round, whereas a winewith bad tannins we ndwith bad tannins we ndunripe, hard, coarse,unripe, hard, coarse,

and bitter.and bitter.


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was repeated and again, the winner wasa Cali ornia Cabernet Sauvignon (1971Ridge Vineyards Monte Bello). Tese re-

sults suggest that it is indeed possible toproduce age-worthy wine in such a way that it can be consumed when young ora er a considerable amount o time.

TIMING TANNINS

Te process o optimizing tannin concen-tration and composition in red wines occursat all stages o production and in a variety o ways. In the vineyard, research has shownthat wines made rom increasingly ripe ruittend to have a more desirable texture. Yet,grapes that are le to ripen too long risk developing so much sugar content that theresulting wine is excessively alcoholic, and isthere ore perceived as hot in the mouth.During the winemaking process, the er-mentation temperature and the contact o the new wine with the skins and seeds in u-ence the extraction o tannins and thus thebalance o the wine. Skill in wine productionis knowing when to separate the skins andseeds rom the new wine. Premium winesare generally aged in small oak barrels.When they age in barrels the tannins oxi-dize (and thus so en) at a more rapid ratethan they would in the bottle, so cellaringtime is another critical actor. Tis is a sig-nifcant cost to wineries because o the bar-rel and time investment. Recent advances inwine production practices have acceleratedthis process and reduced the cost by incor-porating oak in wine stored in stainless steeltanks along with micro-oxygenation.

THE FUTURE OF WINE RESEARCH

Te comparatively recent progress in ourunderstanding o grape and wine tanninsserves as a good example o how the wineindustry is better served when scientists

and cra smen can work side by side touncover the secrets o a centuries-old tra-dition. An example o how wine sciencehas contributed immensely to the successo our global wine industry is seen in theemergence o commercial winemaking inparts o the world that have had little inthe way o wine history. For example, inOregon, the wine industry is based upon vineyards that were planted on sites with-out prior grape production experience.

Moreover, the most signifcant varietalin Oregon is Pinot noir, a varietal notori-ously di cult to produce well.

And Oregon isnt alone in its achieve-ment. Other wine producers have doneas well in Australia, Chile, New Mexico,South A rica, exas, and many other new and emerging winemaking areas. Whattook centuries to achieve in well-estab-lished lands, new wine-producing regionshave achieved in mere decades. Grape andwine scientists o the world: give yourselvesa collective pat on the back. Job well done!

Where does wine tannin research gorom here? Here are some examples o projects that are currently in progress andhow they are designed to contribute to theprogress o our fne wine industry.

Spatial Variation in Grape and WineTannins. In many parts o the world, vine-yards are planted in sites that are ar romuni orm (e.g., soil, aspect, elevation, nutri-ent availability). Tis makes the ruit asheterogeneous as the site. rans erring thisheterogeneity into a ermentation tank isnot desirable because it makes wine quality a guessing game. Using precision agricul-ture tools, this heterogeneity can be mappedout and the vineyard management practicescan either be modifed to try to minimizethe heterogeneity or the winemaker can usethis in ormation to make harvesting deci-sions. Based upon our research fndings,understanding how site variation in uencestannin chemistry can have a large impact onthe entire winemaking enterprise.

Infuence o Grape Cluster Tem-perature on Composition. Te immedi-ate climate around a grape cluster can pro-oundly a ect its composition at harvest.Understanding how specifc microclimateactors (e.g., light, temperature, relative hu-midity) in uence grape composition could

change grape management practices andour ability to predict e ects due to climatechange. Working with United States Depart-ment o Agriculture micrometeorologist Ju-lie Tarara , the Food Science and echnol-ogy department at Oregon State University is investigating how cluster temperature in-uences grape tannin composition.

Relative Extraction o Skin and SeedTannins. When tannins are extracted romthe grape into new red wine, they generally

come rom two sources, the skin and seedo the berry. Research has shown that thesetannin pools have di erent compositions.

Anecdotally, it is thought that seed and skintannins have di erent sensory properties inwine. Winemakers have developed produc-tion methods to accentuate the presenceo one or the other tannin based upon thisanecdotal evidence. Te problem: How doyou di erentiate skin tannin rom seed tan-nin once extracted into wine? Tis problemwas recently solved1 and we are now study-ing how specifc grape and wine productiontechniques in uence the extraction andpresence o these tannin pools in wine, andmore importantly, their corresponding sen-sory properties.

SCIENCE AND CRAFTMANSHIP

Wine history predates western civilizationitsel , and it is not surprising that wineproduction today is steeped in tradition.Despite the many advances in wine sci-ence, rom a traditionalists perspective, ito en seems that the product o wine sci-ence is dull and uninteresting. Yet I wouldargue that at no other time in the history o wine have so many fne age-worthy wines been readily available. Wine sciencehas been instrumental in this progress. Sopour yoursel a fne wine and toast to theaccomplishments o wine science!

James Kennedy is an assistant pro essor in thedepartment o Food Science and echnology at Oregon State University. His research ocus ison grape and wine chemistry, with much o hiscurrent research in the area o red wine pheno-lics and how they relate to wine quality.

Note:1. Peyrot des Gachons, C.; Kennedy, J.A.

(2003) Direct method for determining seedand skin proanthocyanidin extraction into

red wine. Journal of Agricultural and Food Chemistry 51, 5877-5881.

Here lies the source of one of the fundamental schisms in the wine-producing woHere lies the source of one of the fundamental schisms in the wine-producing woshould a wine be drunk? Wines consumed within a couple of days . . . should conshould a wine be drunk? Wines consumed within a couple of days . . . should conlower concentrations of tannin. Wines meant to be aged should contain lots of talower concentrations of tannin. Wines meant to be aged should contain lots of ta

Listen to a podcast of James Kennedystalk, A Toast to Tannins, at the Decem-ber 15, 2006 Science of Wine event at the

Academy, part of the Science of Foodseries, by going to www.nyas.org/podcast

on the web

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The New York Academy of Sciences Magazine -- The Science of Red Wine