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BY James Kennedy, Department of Food Science & TechnologyOregon State University, Corvallis, OR

In the world of winemaking, thereis a universal truth about the qual-ity of the vintage: It is directly cor-related with optimal grape matu-

rity. Site selectionand grapegrowingpractices have atremendous influ-ence on achievingoptimal maturity.

A considerableamount of viticul-tural research hasidentified strate-gies that can beused to optimizegrape maturity atharvest includingirrigation,1,2,3 canopymanagement,4–9 andcropping lev-els,10,11,12 among oth-ers.13–16 To fully ap-preciate how thesestrategies can beused to optimizegrape maturity,grapegrowers andwinemakers shouldhave an under-standing of berrydevelopment.

Fruitdevelopment

The grape berry isessentially an inde-pendent biochemi-cal factory.17 Be-yond the primarymetabolites essentialfor plant survival (water, sugar, amino acids,minerals, and micronutrients), the berry hasthe ability to synthesize all other berry com-ponents (for example, flavor and aromacompounds) that define a particular wine.

There is a potential for tremendousvariability in ripening between berrieswithin a grape cluster, and thereforewithin the vineyard.18,19,20 Practicallyspeaking, it is difficult to determinewhen a vineyard with a large varia-tion in berry maturity is at its best pos-sible ripeness. One of the major objec-

tives of modern viticulture is to beable to produce a uniformly ripe crop.

If premium winemakers were tocome up with what constituted theideal, optimally ripe vineyard, it

would be uniformly ripe clusters withsmall berries chock-a-block with flavor.An understanding of berry anatomy,when and where berry components areproduced, is the first step in under-standing the rationale behind manag-ing wine style in the vineyard.

Berry structureFrom a wine-

making perspec-tive, the grapeberry has threemajor types of tis-sue (Figure I):flesh, skin, andseed, with thesheer bulk of winebeing derived fromthe flesh. Thesetissues vary con-siderably in com-position, andtherefore by exten-sion, they con-tribute differently tooverall wine com-position. Becauseof this, the compo-sition of wine canbe manipulatedby simply chang-ing berry size. Asa general rule,wines made fromsmaller berries willhave a higher pro-portion of skin andseed derived com-pounds.

In addition tothe effect of berrysize on the propor-tion of skin and

seed-derived components in wine, theactual number of seeds in the berry caninfluence the proportion of seed-derivedcomponents in wine. The normal or per-fect number of seeds in the grape is four;21

Understanding grape berry development

Figure I: Structure of a ripe grape berry partially sectioned on the long and central axis toshow internal parts. Illustration by Jordan Koutroumanidis, Winetitles.

in general though, the actual number ismuch less.

Environmental and nutritional con-ditions at bloom time affect the successof fertilization, and the resultingnumber of seeds per berry,20,22,23,24 andtherefore can be expected to influencethe presence of seed-derived materialin wine.

The berry is supplied through theberry stem or pedicel by a vascular sys-tem composed of xylem and phloemelements. The xylem is the vasculatureresponsible for transporting water,minerals, growth regulators, and nutri-ents from the root system to the rest ofthe vine. Current evidence indicates

that xylem is functional in grapeberries early in development (up tovéraison), but afterward, its function isreduced or eliminated.25

The berry is also supplied by thephloem, which is the vasculatureinvolved in photosynthate (sucrose)transport from the canopy to the vine.It has reduced function early in berrydevelopment, but becomes the pri-mary source of ingress after véraison.25

Increases in berry volume (primar-ily water) are associated with increasesin sugar after véraison. However, insome grape varieties (most notablySyrah), sugar increases during the lat-ter stages of fruit ripening are not

accompanied by increases in berry vol-ume, but are caused by berry shrink-age. This shrinkage appears to be dueto the transiprational loss of water,26,27,28

suggesting that the inability of theberry to stay well-hydrated at thispoint is due to blockage of phloem ele-ments into the berry. This indicatesthat, for some varieties, the vasulaturebetween the vine and the berries hasreduced function during late seasonfruit ripening.

Development during first growth period

Berry development consists of twosuccessive sigmoidal growth periods sep-

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0

Ber

ry S

ize

Xylem

Xylem flow ceases

Flowering Days after flowering

BERRY FORMATION BERRY RIPENING

20 40 60

4ºBrix 7 10 14 18 22 26

80 100 120

Phloem

pericarpcell division

Periods whencompoundsaccumulate

setting

Veraisonlag phase

Engustment

Tartrate Tannin Hydroxycinnamates Methoxypyrazine Malate Glucose Fructose Anthocyanin Flavour compounds

Figure 2: Diagram showing relative size and color of berries at 10-day intervals after flowering, passing through major developmental events(rounded boxes). Also shown are the periods when compounds accumulate, the levels of juice obrix, and an indication of the rate of inflow ofxylem and phloem vascular saps into the berry. Illustration by Jordan Koutroumanidis, Winetitles.

arated by a lag phase (Figure II).18 The firstperiod of growth lasts from bloom toapproximately 60 days afterward. Duringthe first growth period, the berry isformed and the seed embryos are pro-duced. Rapid cell division occurs throughthe first few weeks, and by the end of thisperiod, the total number of cells withinthe berry has been established.29 Theextent of cell division has some bearing onthe eventual size of the berry.

Also during the first growth period,the berry expands in volume as solutesaccumulate. There are several solutesthat accumulate in the berry during thefirst growth period, all of which reachan apparent maximum around vérai-son.30 By far the most prevalent amongthese are tartaric and malic acid.

These acids are distributed in theberry somewhat differently, with tar-taric acid being highest towards theoutside of the developing berry, andmalic acid being highest in the flesh.Tartaric acid appears to accumulateduring the initial stages of berry devel-opment, and malic acid accumulatesjust prior to véraison. These acids pro-vide wine with acidity and are there-fore critical to wine quality.

Also accumulating during the initialperiod of growth are the hydroxycinnamicacids.31 Hydroxycinnamic acids are dis-tributed in the flesh and skin of the berryand are important because of theirinvolvement in browning reactions, andbecause they are precursors to volatilephenols.32

Tannins including the monomericcatechins also accumulate during thefirst period of growth.33,34 Tannins arepresent in skin and seed tissues andnearly absent in the flesh, and areresponsible for the bitter and astrin-gent properties of red wine. Thesecompounds are also believed to beimportant in red wine color stability.

There are other compounds thataccumulate in the berry during thefirst phase of growth, and which haveimportance to wine quality.Minerals,30 amino acids,35 micronutri-ents, and aroma compounds (such asmethoxypyrazines36,37) have all beenobserved during the first period ofberry growth.

Our understanding of berry forma-tion and development during the firstperiod of growth and of the productionof compounds having sensory impor-tance is still developing. Under-

standing berry formation and the fac-tors that affect its formation is still lim-ited because of the complex nature ofthis type of research.

Understanding berry developmentand its compositional changes during thefirst growth period is limited probablybecause the compounds produced arethought to be of less interest from a sen-sory standpoint. It should be rememberedthough, all compounds discussed aboveare critically important to wine quality.

Development during second growth period

The beginning of the second phase ofberry growth or fruit ripening (véraison)is characterized by softening and color-ing of the berry. Overall, the berryapproximately doubles in size betweenthe beginning of the second growthperiod and harvest. Many of the solutesthat accumulated in the grape berry dur-ing the first period of developmentremain at harvest, yet due to the increasein berry volume, their concentration isreduced significantly.

Some compounds produced duringthe first period of growth are reducedon a per-berry basis (not simplydiluted) during the second period ofberry growth. Principal among these ismalic acid. Its reduction varies consid-erably but can roughly be correlatedwith climate. That is, grapes grown inwarmer regions tend to have less malicacid than those grown in cooler regionsas a result of this reduction.

Tannins also decline considerablyon a per-berry basis during the secondperiod of growth. The reduction inseed tannin appears to be due to oxida-tion as the tannins become fixed to theseed coat.38 As a result of this, the com-position of extracted seed tanninschanges considerably, and is character-ized by a proportional reduction in themost bitter tannin components.

Skin tannins decline or remain con-stant during the second period ofgrowth, and also become modified.Significant modifications that takeplace for the skin tannins include anincrease in their size. Also of potentialsignificance from a wine quality stand-point is evidence that extracted skintannins are modified with pectins andanthocyanins.33 This could make berrydevelopment an important considera-tion in the areas of wine texture andcolor stability.

Notable aroma compounds that areproduced during the first period ofgrowth, decline (again, on a per-berrybasis) during fruit ripening. Theseinclude several of the methoxypyrazinecompounds that contribute vegetal char-acters to some wines (such as CabernetSauvignon and Sauvignon Blanc).39 Thedecline in pyrazines is thought to belinked to sunlight levels in the cluster.Therefore, if these compounds aredeemed to be undesirable (the currentprevailing opinion), then canopy man-agement can be used to reduce them.

Despite these major changes in com-pounds produced during the firstgrowth period, the big story during thesecond growth period is the tremen-dous increase in compounds (the majorones being glucose and fructose) thatoccurs as a result of a total biochemicalshift into fruit ripening mode.

Beginning at véraison, sugar influxinto the berry commences. Sucrose pro-duced from photosynthesis is importedinto the grape berry during fruit ripen-ing. Once transported into the berries,the sucrose is hydrolyzed into its con-stituent sugars glucose and fructose.40

Their eventual concentration is dictatedpartly by the length of time the grapeberry is allowed to stay on the vine.(Other factors include the crop load,canopy size, disease status, and as men-tioned earlier, dehydration).

Beyond sugar accumulation, themajor determinants of a wine’s qualityare the secondary metabolites. In redgrape varieties, anthocyanin production(restricted to skin tissue in most culti-vars) is probably the most obvious com-pound of importance, but as with whitevarieties, most of the volatile flavor com-ponents are produced during fruit ripen-ing.41–45 These would include such com-pound classes such as terpeneoids,which are important to the pleasantaroma of many varieties, such as Rieslingand Muscat, and fruity aroma precur-sors. Aroma compounds are distributedin the flesh and skin of the berry.

In addition, many other importantaroma and flavor compounds are pro-duced late in fruit ripening. Some ofthese components are produced asprecursors, and are not actuallyvolatile until after the wine has beenproduced and aged for some time.46

Nevertheless, their precursors are pre-sent in the grape as glycosides, and theperiod of time where many of them

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appear to be produced has recently beengiven the term “gustation.”47

In examining berry development, ithelps to look at it from an ecologicalperspective. If the raison d’être for theberry is to reproduce, then its first pri-ority is to develop a viable seed.During the first period of growth theberry does just that. It develops aviable seed and produces compoundsto protect it while doing so.

If you think about the compoundsthat are produced during the first periodof growth (organic acids, tannins,pyrazines), they combine to make forag-ing by birds and mammals a downrightunpleasant experience. By the end of thefirst period of growth, a viable seed hasbeen produced, and therefore, the goalduring the second period of berrygrowth is to make the berry as appealingas possible to birds and mammals so thatseed dispersal can occur.

ConclusionMany advances have been made in

understanding of how the grape berrydevelops and of the components that areimportant in wine. No doubt the qualityof our wines has improved as a directresult of being able to manipulate thegrape berry through production practices.

Understanding when various compo-nents accumulate in the berry is criticallyimportant to understanding how grape-growing practices can be used to modifywine style. It is clear that this is an area ofresearch that will continue in the future,yet it is already apparent that a wine-maker can influence wine style throughgrapegrowing practices. The trick isunderstanding the what, when, and howof berry manipulation. ■

Illustrations provided by AustralianViticulture from text: “Ripening berries —a critical issue” by Dr. Bryan Coombe,(Honorary Visiting Research Fellow,Adelaide University, Australia) and TonyClancy (Editor, Australian Viticulture),March/April 2001. Illustrations preparedby Jordan Koutroumanidis.

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berries cv. Shiraz caused by impededphloem transport?” Australian Journal ofGrape & Wine Research 5: 17-21.

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