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Current Eamments@ EUGENE GARFIELD INSTITUTE FOR SCIENTIFIC lNFORMATION~ 3501 MARKET ST PHILADELPHIA PA 19104

Enology. Part 1. Fortifying an Ancient Art with Modem Science

Number 29 )UIY 20, 1987 For the past few years, Philadelphia has content falls much below 7 or 8 percent, the been experiencing a restaurant “boom’ ‘— beverage approaches what is now called a a renaissance of creative dining establish- “ cooler, ” a combination of undistin- ments. 1.2In addition to exotic foods pre- guished wine and unfermented fruit juice. pared in unusual or extravagant ways, a sig- The alcohol content of varies, of nificant part of this gastronomic revolution course. In some cases, with grapes that are has been the prominence of wine as a part very high in , alcohol levels may reach of the meal and an accompanying increase 14 percent; others can be as low as 7 per- in interest in types of wines and how they cent.5 (p. 43) The alcohol content of cham- are served. pagne and sparkling wines generally ranges One of my own favorites is Piesporter, a from 10 to 12 Percents (p. 178-90) If the term that, according to the Encyclopedia of bottle indicates alcohol content above 14 Wine by the eminent wine writer Frank percent, then a neutral has beerradd- Schoonmaker (1905-1976), refers to wines ed (as in port, sherry, and other dessert produced in the village of Piesport in the wines). j (p. 191-203) Wines that have not Moselle Valley of the Federal Republic of only a relatively high alcohol content (15 Germany-although some wines labeled percent or more) but also other natural fla- ‘‘Piesporter” may come from “less cele- vors—including herb flavors-are called brated townships nearby. ” Schoonrnaker aperitifs.5 (p. 204-1 1) described Piesport as “one of the small yet Goldtropfchen wines are sweet because deservedly one of the most famous not all of their natural grape have wine-producing” sites along the Moselle and been converted into alcohol during fermen- called genuine Piesporter wine “wonderful- tation; they have no synthetic or natural ly delicate and fragrant, fruity, with an in- sugar added to sweeten them. While my comparable distinction all its own.”3 A tru- more sophisticated friends continue to ‘‘ed- ly great Moselle wine is created by a selec- ucate” me to the virtues of other wines, my tion process that involves picking grapes col- particular chemical makeup doesn’t react onized by the “noble mold” Botrytis cin- well to dry wines or stronger alcoholic erea, which grows naturally on late-harvest- drinks. Some of these friends helped in ed grapes and depletes them of their mois- preparing this report, including my neighbor ture, thus concentrating their inherent sugar and good friend, wine enthusiast Arthur and flavor. ‘r Bayard; Arthur Seidel, patent attorney and As a matter of fact, my preference for scholar extraordirraire; and Morley Kare, Piesporter is even more spexitic-piesporter director of the Monell Chemical Senses Goidtropfchen (Golden Drops), of which Center, just across the street from lSl@. there are at least a dozen brands that I’ve Wine is the subject of considerable sci- encountered. But to paraphrase the Ameri- entific interest. Part 1describes some of this can humorist Will Rogers, I never met a published scientific research. Part 2 will Goldtropfchen I didn’t like. These sweet, discuss the leading centers of enology re- white wines are about as low in alcohol as search around the world. I imagine, how- you can get in a true wine—if the alcohol ever, that there is considerable “research”

190 in this field that remains unpublished. Most broadest sense, “wine” refers to the fer- likely, these trade secrets remain closely mented juice of any piant product; wine guarded because patents provide less than made from dandelions, a common iawn pest a generation of protection. For most inven- in North America, is popular in some parts tors, this is inadequate incentive. of the US, and the Japanese produce a wine, called , from fermented rice. Another popuiar Japanese fruit wine is made from Just What Is Wine? piums. It is ciose to a sherry in taste, and Wine has been a part of human cuiture for I’ve encountered at least a dozen brands in millemia. The word “wine” derives from Japanese and Chinese restaurants in the US. the ancient Greek word oinos, from which , of course, is the process came the Latin vthum and the Old and Mid- that makes wine possible. The chemistry of die Engiish forms of the word, win and wyn, fermentation-the conversion of a moiecule respectively. b /Uso derived from oinos is of grape sugar (glucose) to two molecules the far more modern word ‘‘ecology, ” the of alcohoi (ethanoi) and — science of wine and wine making. T was first described by French chemist Jo- “Wine” usually refers to the fermented seph Louis Gay-Lussac in 1810.1o.11How- juice of grapes-specifically, to the juice of ever, Louis Pasteur demonstrated in i 857 the Old World wine grape, Vitis viru’’era.8 that the process is due to the metabolic ac- (Vitis, the name of the genus to which this tions of ceiis (generaiiy of the Sacchar- plant belongs, is the Latin word for omyces cerevisiae species). 12.ls The chem- “grapevine”; vinifera is the species icai equation for this process is reproduced name.g) The variations of V. vinifera, in Figure i. which range from light greenish yellow But wine is a compiex liquid whose final through russet, pink, red, reddish violet, and flavor is influenced by numerous factors. Of purplish black, account for the vast majori- course, the amount of time the wine is ai- ty of fine grape wines. Other factors con- lowed to ferment is one such factor, but tributing to the diversity of these wines (as there are many others that affect flavor be- well as those made from other grapes) in- cause they affect the maturation of the clude the climate and soil conditions under grapes. These inciude moisture, suniight, which the grapes are grown, the techniques soil conditions (such as rninerai content), as of the wine makers, and the actuai processes well as any fungi, molds, and diseases that used during vilification (the conversion of may attack the vines (and thereby affect the juices into wine). ripening process). Even the temperature of But while V. vinifera is the fruit of choice the grapes when they are picked can influ- for most “noble” or distinguished wines— ence the flavor of the finai product. 11Not that is, those rhat are aged in the bottie— surpnsingiy, two of the 1986 1S1research most wines are produced from hybrid vines. fronts we identified in reiation to wine and Wines are produced from an array of grape wine making concern the yeast S. cerevis- varieties. For instance, the Concord grape iae (see Table 1). Three other fronts de- (V. kdwusca)–aiso known as the wild scribe new methods for the chromatograph- American fox grape and a native of the ic and spectrai analysis of the various con- eastern US—is one of the main alternatives stituents of wine. to V. vinifera.s (p. 25) The juice of other grape varieties, such as the Muscadines (V. Resemch-Frortt Data rotwtdifolia) and the desert grape (V. gir- diana), as weii as V. rupestris, V. ber,!an- In i986 there were 27 pubiished papers dieri, and V. riparia-ail of which are na- concerning’ ‘Computer regulation of sugar tive to North America-is aiso used occa- metabolism in yeast” (#86-0359). Waiter sionally to make wine, aithough their main Beyeler, Swiss Federai institute of Technol- use iies in serving as rootstock or as the ogy, Zurich, coauthored two of the four core parents of hybrid grape varieties.s (p. 25)$ papers that identified this topic. With col- In fact, the juice of any fruit can be fer- leagues Arthur Einsele and Arntin Fiechter, mented to produce wine. Indeed, in its he wrote a paper in i 98i describing a new, Tstbte 1: The 19S6 SCP /SSCP research fronts on vxrious aspects of enology. A =number of core papers. B=rtumber of citing papers.

Nmrtber Name AB

86-0359 Computer regulation of sugar metabolism in yeast 4 27 86-0360 -sensitive mutants of .%charomyces cerevisiae 4 35 86-2020 Current trends in wine tdsnology 16 131 86-6056 Determination of wine components by gas chromatography 2 13 86-8351 HPLC and spsctrd methods for separation of phenolic compounds 2 15

to keep track of the rate at which glucose Figure 1: The chemicaf equation for the conversion of was being metabolized and could add glu- glucose to alcohol. cose as needed to keep the level optimaJ. IT 1 glucose (CCH,20J ~ 2 ethanol (CH3CH20H) + A]ba also coauthored one of the four core 2C02 + about 56 kilocalories of energy papers for the research front on ‘‘Etha- nol-sensitive mutants of .$accharornyces cerevisiae” (#86-0360). His 1%8 paper dis- computerized prob for measuring fluores- cusses the growth rates of a specific strain cence in cultures of microorganisms. 14Ul- of S. cerevisiae under various concentra- traviolet light is used to cause the nicotin- tions of alcohol. la Alcohol, the natural arnide adenine dinucleotide phosphate product of fermentation, inhibits the meta- (NADP, which mediates oxidation and re- bolic activity of the yeast cells in concen- duction by carrying electrons) contained in trations of more than 20 percent. This in- yeast microorganisms to fluoresce; by hibitory effect was also the subject of two measuring the intensity of this fluorescence, core papers coauthored by D. Susan Thomas the amount of microorganisms contained in and A. H. Rose, Zymology Laboratory, the sample and their rate of growth can be School of Biological Sciences, Bath Urtiver- accurately estimated. Since different wines sity, UK. (Zymology is the study of en- are made by varying the length of the fer- zymes and metabolic processes.) One paper, mentation process, measures of fluorescence coauthored in 1978 with J. A. Hossack, dis- allow the process to be more precisely ar- cusses a method of increasing the resistance rested at any stage. Beyeler’s other paper, of S. cerevisiae to alcohol, 19 while the coauthored with colleague C. Meyer in other, published a year later, followed up 1984, is an analysis of methods used to con- on the earlier work.zo The fourth core trol the rate of microbial reactions in paper, by Tilak W. Nagodawithana and culture. 15 Keith H. Steinkraus, Cornell University, Another core publication for front New York State Agricuktu-al Experiment #86-0359, published in 1968, discusses the Station, Geneva, discusses the effects of spe- actions of seven different enzymes (includ- cific levels of alcohol on the growth of ing NADP-linked glutamate dehydrogertase) S. cerevisiae.21 in the growth of S. cerevisiae under various Figure 2 is a historiograph showing the concentrations of glucose. 16The interaction research leading up to front #86-0360. As of yeast and glucose is the subject of a 1976 noted previously, these historiographs, or core paper by Shuichi Alba, Shiro Nagai, microhistories of the research in a given and Yoshinon Nishizawa, Institute of Ap- field, demonstrate the continuity of research plied Microbiology, University of Tokyo, from year to year. But they can also show Japan. ITIt discusses a method of avoiding the consolidation of several lines of research the “glucose effect, ” a phenomenon in or indicate where a new line breaks away which “aerobic fermentation” (the partial from an old one. aerobic metabolism of glucose) occurs if the Whereas the above research fronts address concentration of glucose rises above a cer- aspects of the biology of wine making, tain level. By measuring the concentration others concern the chemical analysis of of alcohol in the medium (an indireet mea- wine. One emerged in 1986 and is entitled sure of fermentation), the authors were able “Determination of wine eomporsentsby gas

192 Figure 2: Histmiograph of current research on ethanol production, yeast fermentation, and wine-making technology. The numbers of cordciting documents are at the bottom of each hex, Variations from year to year in clustering methods may account for the dkorrtinuous configuration of the historiograph.

85.2008 86.2020 Synthesis of Currwrttrends m casqrritwpwmc in wine biologicalcom- and otheralcohol pounds by immo- ‘---7 glycosidss in relation bilized cells and to aroma and flavor L5uu_-J errzymm of grapes and wines 86.0360 30/249 12/89 j____. j Etharrokencitive nmtants of 83-2513 84.0018 85.3405 Saccharomyce.r Ethanol Aspects of Ethanol cwevisiae fermentation and ethanol Dmduction production from 4135 aspectsof errzp XYIOSSfermerrts- matic hydrolysis tion hy yeact n86.6351 17/209 5/43 HPLC and spectral methods far scparetirrn of 83.7598 85.0341 ph8110hC compounds Ethanol pro. Continuous alcohol 2116 duction by xvloaa- fnrmerrtation in fermentirrg yaact immobilized micro. 3/26 bird whole cells jn86JJ359 84.0937 35/221 Computw regulation of suwr metabolism In83-0352 I Oxygen Alcoholic yeast requirements and in yeast fermentation: other aspectsof 4127 I ethanol prodrm l.- growth conditions n P 86.6056 I Oetwminatiorr of wine components by gaschromatography u2113 chromatography” (#86-6056). It concerns Figure 3: Chemical etructure of an arrtfmcyanirr, one of methods of deteeting diethylene glycol, a the natural pigments found in wine, compound found in antifreeze and lubricants that “recently has been added illegally to certain wines in Austria, West Germany, and Italy, ” according to Cornelius S. Ough, professor of enology and chairman of the Department of Viticulture and Enology, University of Californut, Davis. “A rela- tively small amount of the materifd gives wine a mouth-filling feel and enhances its sweetness. However, it is highly toxic.’ ’22 OH One of the core publications for this front is Clinical Toxicology of Commercial Prod- ucts, a book written by Robert E. Gosselin The other core document is a quarterly in- and Roger P. Smith, Dartmouth MWIcrd dex of poisonous substances and common School, Hanover, New Hampshire, and items in which they are found, such as clean- Harold C. Hedge and Marion N. Gleason, ing products. 24 Since wines contain etha- School of Me&cine and Dentistry, Univer- nol—which, of course, is toxic in unusual- sity of Rochester, New York.2g Cited over ly large amounts-they are listed alphabeti- 230 times from 1957 through 1986, it pro- cally by brand name and manufacturer. vides exhaustive information on the toxici- The index is edited by Barry H. Rumack, ty of virtually every poisonous compound Rocky Mountain Poison Center, Denver, found in commercially producsd substances. Colorado. 193 In a highly competitive industry where allyhc pyrophosphates m the synthesis of everyone wants to know what components isoprenoid metabolizes.28 Pyrophosphates make for better-tasting wine, analytical are water-soluble compounds, some of methods are important. Thus it is not sur- which serve as the precursors of various ter- prising that a research fronton “HPLC and Penes,zg a class of about 5,000 structurally spectral methods for separation of phenolic related compounds that are made up of van- compounds” (#86-835 1) turned up. HPLC ous numbers of isoprene units (C5H8).29s30 refers to high-pressure liquid chromatogra- Terpenes and isoprenes—including mono- phy. It involves the use of tiny, high-pres- terpenes, which are made up of two isoprene sure tubes to separate the constituents of a units (10 carbon atoms)—were the subject solution for analysis. 25Phenols include an- of a 1953 paper by L. Ruzicka, Laboratory thocyanins, the pigments that produce most of Organic Chemistry, Swiss Federal Insti- red, purple, and blue colors in multicellu- tute of Technology,31 and a book chapter lar plants; they are the only significant by Rodney Croteau, Institute of Biological pigments in red grapss.s (p. 48) Other Chemistry and Biochemistry/Biophysics phenols found in grapes are the light yellow Program, Washington State.Jz Ruzicka’s anthoxanthin pigments in the skins and swds paper detailed the chemical strucmres of nu- of white-wine grapes. Figure 3 shows the merous terpenic compounds and described chemical structure of an anthocyanin pig- the reactions that produce them and the com- ment. pounds for which they, in turn, are precur- Phenols are the subject of a 1969 book by sors.q1Croteau’s quite recent article (1984) Vernon L. Singleton and Paul Esau, Depart- discussed the origins, production, and break- ment of Viticulture and Enology, Universi- down of monoterpenes, which constitute the ty of California, Davis. It provides qualita- “characteristic components of the essentird tive and quantitative descriptions of the phe- oils” of higher pktnts.sz nolic composition of grapes and wines and Another article that is core to this front discusses the impact of these compounds on involves gas chromatography. 33This meth- the flavor of wine.zG Phenols originate in od traps the components of the mixture be- grape skins and seeds and in the oak from ing analyzed in a stream of an inert, inor- the barrels used to age some wines. They ganic gas. The constituents are then briefly are responsible for the color, bitterness, as- absorbed in a liquid or solid through which tringency, some odors and flavors, and an- the gas is passed. The various compments tioxidant characteristics of wine. This book are absorbed at different rates, according to and a paper by Larry W. Wtdf and Charles their chemical composition; this results in W. Nagel, Department of Food Science and differences in the retention times in the col- Technology, Washington State University, umn of the instrument, allowing the constit- Pullman, on the use of HPLC to isolate and uents to k isolated. 25 quantify the various anthocyanin pigments Itis interesting to note that another core in two types of V. vinifera grapesZThelped document for front #86-2020 is George W. to identify research front#8@3351. Through Snedecor’s Statistical Methods Applied to co-citation analysis, just a pair of well-cited Experiments in Agrictdture and Biology,34 works can pinpoint complex subject matter. now 50 years old. We published a commen- There were 15paprs published on this topic tary on this Citation Classicm, written by in 1986. his coauthor, statistician William G. Coch- The largest 1986 research front explicit- ran, Harvard University, Cambridge, Mas- ly comected to wine making is entitled sachusetts, in 1977.35 (Snedeeor dkd in “Current trends in wine technology” 1974; Cochran authored a chapter analyz- (#86-2020) and turned up 131 citing publica- ing sample surveys for the fi~ edition of tions. A sampling of the 16 core documents Snedecor’s book, which appeared in 1956.) cited by these publications shows how basic It and many other similar works are cited some of the research on wine is these days. by nonmathematicians who apply statistical In 1980 David E. Cane, Department of analysis to their raw data. It is easy to un- Chemistry, Brown University, Providence, derstand why such books continue to be Rhode Island, wrote a review of the role of cited. However, it also illustrates how co- 194 cited documents that are in fact themselves from these institutions, and the journals that unrelated in subject matter can together de- publish ecological research. fine a precise subject area. ***** This concludes our discussion of current research in wine making; in Part 2 we will My thanks to Stephen A. Bonaduce and describe the Ieadmg institutions for wine re- C.J. Fiscus for their help in the preparation

search tcday, some of the highly cited papers of this essay. eI987 ,s1

REFERENCES

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