Pigment development during ripening oi the grape

Using marked berries from a single Shiraz grape cluster in a vineyard at Magill, South Australia, the composition of extractible grape pigment was examined over a 50-day period from veraison to post-harvest. The analyses of total skin extract were made by gel column chromatography, from which measures of acylated anthocyanins, anthocyanins and tannin pigments were obtained.Acylated anthocyanins were present from the earliest stages, and the levels of both acylated and non-acylated anthocyanins became maximal at 20 to 30 days after veraison, when the Brix value was 21 to 24 degrees. There was a decline from a maximum of about 1.0 mg total extractible anthocyanins per berry around day 20 to about 0.7 mg per berry approaching day 50; this decrease was associated with shrinkage of the berries.The tannin fraction was initially yellow and averaged 0.7 mg/berry at day 1. In the first few days after veraison, there was sharp increase in the quantity of this fraction per berry (to 2.4 mg at day 4) with fluctuation thereafter between 2.1 and 4.3 mg!berry (mean 3.1 mg from day 4 to day 50). There was also progressive change in spectral characteristics up to about day 30, with increasing pigmentation in the samples isolated during this period.The grape tannin pigments are considered to be artefacts arising from the use of HCI in the extraction and measurement of extremely labile phenolic materials, but their facile formation in such conditions is relevant to interpretations of the normal course of ageing reactions in red wines.Die Pigmententwicklung während der TraubenreifungAn gekennzeichneten Beeren einer einzigen Traube der Sorte Shiraz wurde über einen Zeitraum von 50 Tagen vom Weichwerden bis nach der Ernte die Zusammensetzung der extrahierbaren Traubenpigmente untersucht. Die Analyse des Gesamtextraktes der Beeren erfolgte durch Säulenchromatographie an Sephadex G25, wobei Daten über die acylierten und nichtacylierten Anthocyane und die Tanninfarbstoffe gewonnen wurden.Die acylierten Anthocyane lagen schon in den frühesten Beerenstadien vor; acylierte und nichtacylierte Anthocyane erreichten ihre Maximalkonzentration 20-30 Tage nach dem Weichwerden der Beeren bei 21-24 °Brix. Von einem Maximum mit ca. 1,0 mg extrahierbaren Gesamtanthocyanen je Beere um den 20. Tag ging die Anthocyanmenge auf ca. 0,7 mg je Beere gegen den 50. Tag zurück; diese Abnahme war vom Schrumpfen der Beeren begleitet.Die Tanninfraktion war anfänglich gelb und betrug am 1. Tag durchschnittlich 0,7 mg je Beere. In den ersten Tagen nach dem Weichwerden nahm der Gehalt dieser Fraktion je Beere stark zu (bis auf 2,4 mg am 4. Tag); danach schwankte er zwischen 2,1 und 4,3 mg je Beere (Mittelwert in der Zeit vom 4. bis zum 50. Tag: 3,1 mg). Auch die spektralen Kenndaten veränderten sich bis zum 30. Tag fortlaufend, wobei die Pigmentierung in den während dieser Periode isolierten Proben zunahm. Die Tanninpigmente der Trauben werden als Artefakte angesehen, die durch die Verwendung von HCl bei der Extraktion und die Messung von extrem labilem phenolischem Material entstehen; aber ihre leichte Bildung unter diesen Bedingungen erlaubt Rückschlüsse auf den normalen Ablauf der Alterungsreaktionen von Rotweinen

Pigment profiles of grapes and of wines

Gel column analysis of pigment extracts has been automated, and the distribution of total coloured constituents in terms of tannin pigments, acylated anthocyanins and anthocyanins can now be measured routinely, enabling rapid evaluation of materials. Quantitative determinations of polymeric and monomeric pigments in grape extracts and in young wines have been made from the pigment elution curves. Wine grape varieties from the same viticultural area were found to have characteristieally different elution curves. Evidence Ls presented for one variety that some degree of selective extraction of pigments occurs during normal fermentation on skins, the anthocyanins being more efficently extracted than other fractions - thus the composition of pigments in the new wine differs from that in the grape. Other young varietal wines are also qualitatively different from one another in pigment compositions, which generally resemble those of the grape varieties.Regional differences between grapes and wines oi one variety have been demonstrated, which relate to colour extraction and to the ageing characteristics of the wines from these regions.The gross changes in pigment distribution which occur during ageing of red wines, with progressive loss of monomeric pigments and increase in the relative proportions of tannin pigments are described. The latter fraction is seen to be of primary importance to red wine technology.The elution curves obtained are regarded as pigment profiles of the grapes or wines, and the utility of this concept in viticultural and oenological research is demonstrated

Interpretations of colour composition in young red wines

Recent developments in research on pigment composition and anthocyanin equilibria in red wines have enabled more objective description, and some useful interpretation, of the various wine types and styles.Very large variations in recognised parameters of wine colour have been shown in varietal Australian wines by application of a new analytical method. While there are wide ranges in phenolic content, which normally arise from corresponding variation in the harvest composition, the wine pH and the evel of free S02 are also significant determinants of wine colour density and hue. Data on such influences together with measures of the anthocyanin and total phenolic content, are readily obtained from a set of 6 spectrophotometric observations. The method is proposed as providing a kind of "anatomical description" of a young red wine in terms which relate both to the harvest composition and the wine making method. The utility of this concept in oenology has been emphasized by the showing of correlations between several parameters of wine colour and independent assessments of wine quality.Interpretation der Färbungskomponenten bei jungen RotweinenNeuere Erkenntnisse der Forschung über die Farbstoffzusammensetzung und das Anthocyangleichgewicht von Rotweinen ermöglichen eine objektivere Beschreibung und eine zweckmäßige Interpretation der verschiedenen Weintypen und -nuancen.Durch die Anwendung einer neuen analytischen Methode konnte bei australischen Rotweinsorten eine beträchtliche Variabilität der Parameter, welche die Weinfärbung charakterisieren, aufgezeigt werden. Der Phenolgehalt kann über einen breiten Bereich variieren, wofür normalerweise entsprechende Schwankungen in der Zusammensetzung des Lesegutes verantwortlich sind; aber auch Wein-pH und Konzentration der freien schwefligen Säure stellen wesentliche Faktoren für die Ausprägung der Farbintensität und -tönung dar. Aus insgesamt 6 spektralphotometrischen Bestimmungen können leicht Daten über solche Einflüsse sowie Werte des Anthocyan- und Gesamtphenolgehaltes gewonnen werden.Es wird vorgeschlagen, diese Methode für eine Art „anatomischer Beschreibung" junger Rotweine zu benutzen, wobei Größen verwendet werden, die in Bezug sowohl zu der Zusammensetzung des Lesegutes wie zur Weintechnologie stehen. Die Brauchbarkeit dieser Vorstellungen wird dadurch erhärtet, daß Korrelationen zwischen einer Reihe von Parametern der Weinfärbung und den unabhängig davon gewonnenen Ergebnissen sensorischer Qualitätsprüfungen aufgezeigt werden konnten

Flavonol haze in white wines

The formation of a yellow haze in commercial white wines, and of yellow sediments from both juices and wines, was due to precipitation of quercetin. The vine leaves were found to be the major source of soluble quercetin glycosides, leading to excessive levels of free quercetin after hydrolysis during juice or wine storage. Flavonols were analysed by reversed-phase HPLC. Widespread use of machine harvesting, with higher leaf contamination of the grape crush, is considered to be the primary cause of this new form of wine instability. An enzymatic procedure for detecting susceptibility to such deposition in juices and wines is described

Phenolic assessment of white musts: Varietal differences in free-run juices and pressings

Direct spectrophotometry over the range 250-400 nm enables rapid assessment of juice fractions from commercial juice preparation systems. Attention is focused on spectral estimates of the total flavonoids which increase during skin contact, with increasing must temperature, and particularly during recovery of heavy pressings.Spectral data from many sets of commercial juice fractions, concerning eight grape varieties in several districts, were collated over three seasons, 1987-88-89. Such observations have indicated the prime importance of grape variety in relation to phenolic extract in the juice fractions. The data have suggested the notion of 'spectral recognition profiles' arising from intrinsic varietal differences in the distribution of phenolic constituents within wine grapes.Thus the flavonoid concentration appears to be a significant variable of varietal dry white wine style. Qualitative differences in phenolic composition have also been demonstrated by differential spectrophotometry of model skin extracts at 250-300 nm.Fining treatments with various commercial fining agents had only minor effect on flavonoid levels in juice pressings and in press wines

Evolution of red wines III. Promotion of the maturation phase

Die Entwicklung von RotweinenIII. Beschleunigung der ReifungsphaseAusgehend von der Tatsache, daß die chemischen Reaktionen zu Beginn des Weinausbaus im wesentlichen anaerob sind und durch erhöhte Temperaturen beschleunigt werden können, wurde der Einfluß der anaeroben Lagerung bei 42-45 ° C über einen Zeitraum von 25-40 d verfolgt; als Kontrolle dienten bei normaler Kellertemperatur gelagerte Weine. Die Versuche wurden mit Gebinden junger Rotweine (Shiraz, Cabernet Sauvignon, Malbec) in isolierten Edelstahltanks (250, 1200, 5000 l) durchgeführt. Es wurden stetige Veränderungen bei Komponenten festgestellt, die für Farbe, Geruch und Geschmack wesentlich sind; sie entsprachen den Veränderungen, die sich bei normaler Kühllagerung während eines viel längeren Zeitraumes einstellten. Die spektralen Veränderungen der Farbintensität und -tönung waren von einer raschen logarithmischen Abnahme der Anthocyankonzentration bei Wärmebehandlung begleitet, während sich die Kontrollweine nur geringfügig veränderten. In den behandelten Weinen stabilisierte sich die Färbung, bedingt durch die Zunahme oligomerer Farbstoffe.Es gab keine analytischen oder sonstigen Hinweise auf den nachteiligen Einfluß einer derartigen, zeitlich begrenzten Weinlagerung. Bei Shiraz-Weinen wurde die Entwicklung eines zarten Beerenaromas und -geschmackes festgestellt; gleichzeitig wurde zu Beginn der Wärmebehandlung die vermehrte Bildung von Damascenon beobachtet

Evolution of red wines I. Ambient influences on colour composition during early maturation

Observations of changing colour composition and phenolic content of two new red wines were made during the 12-month -period after vintage. Spectral data were plotted with reference to two storage temperatures (3 and 25 °C), storage under nitrogen and under air headspace, pasteurised and non-pasteurised wines, cold-stabilised and non cold-stabilised wines. Progressive formation of polymeric pigments occurred under nitrogen headspace with much faster reaction rates at 25 °C. The presence of oxygen increased rate of change in colour composition, but data points were erratic. Pasteurisation had no influence on phenolic ageing reactions, nor did prior cold-stabilisation. Two types of phenolic condensation reactions during normal wine ageing are indicated. Interpretations suggest the feasibility of accelerating red wine maturation, while at the same time directing phenolic ageing reactions along controlled lines

Evolution of red wines II. An assessment of the role of acetaldehyde

Factors influencing formation and utilisation of acetaldehyde during red vinification have been examined, with emphasis on its production during primary fermentation and depletfon during early maturation.Acetaldehyde concentrations in new wines were controlled at predictably low levels by addition of SO2 at 30- 50 mg/l before fermentation. There was no appreciable effect from yeast strain, pH or temperature on acetaldehyde production. Significant decrease in acetaldehyde, a-ketoglutaric acid and pyruvic acid, with release of free SO2, occurred during malolactic fermentation. The rate of acetaldehyde consumption in sterile-filtered wine was increased at higher te·mperature and decreased by the presence of free SO2 at high levels. Progressive change in pigment composition of new wines was not influenced by variation in bound acetaldehyde within the range 2-103 mg/l.Acetaldehyde concentration also decreased in a majority of red wines during conservation in commercial cellars. Increases were attributed to abnormal conditions of wine exposure to air. lt was concluded that acetaldehyde formation in wine is probably a surface phenomenon, involving autoxidation of ethanol at the wine interface with atmospheric oxygen. Increase in acetaldehyde during vinification was considered to be adverse in relation to sensory properties and stability of red wine

Red wine quality and style: Diversities of composition and adverse influences from free SO2

Relationships between wine colour composition and the overall quality rating were investigated by analyses of 404 young red wines in two varietal classes from three successive vintages. The wines, of Shiraz and Cabernet Sauvignon from 20 viticultural regions of Australia, had been presented for comparative assessment at the Adelaide Wine Shows of 1974-75-76. There was a large variability in all aspects of phenolic content, in wine colour density and tint, in pH, and in levels of total SO2 and free SO2. The latter was the major influence on pigment equilibria, in which there was up to 10-fold variation in the degree of ionisation of anthocyanins (a). Positive quality factors were wine colour density, the parameter a, coloured anthocyanins, total pigments and total phenolics. Negative factors included colour tint, free SO2 and total SO2. There was no correlation with wine pH. Wide variation in winemaking practice concerning the amount and timing of SO2 additions is considered to have been responsible for much of the range in quality within these groups of wines.Qualität und Nuance von Rotwein: Schwankungen der Zusammensetzung sowie nachteiliger Einfluß von freiem SO2 Anhand der Analysen von 404 jungen Rotweinen - zwei Sorten aus drei aufeinanderfolgenden Jahrgängen - wurden die Beziehungen zwischen den Komponenten der Weinfärbung und der Gesamtnote der sensorischen Qualitätsprüfung untersucht. Die Weine, Shiraz und Cabernet Sauvignon, waren bei den Adelaide Wine Shows 1974/75/76 zur vergleichenden Beurteilung angestellt worden. Sämtliche Parameter des Phenolgehaltes, die Farbintensität und -tönung, der pH-Wert sowie der Gehalt an Gesamt-SO2 und freiem SO2 zeigten eine beträchtliche Variabilität. Das freie SO2 beeinflußte das Pigmentgleichgewicht am stärksten, wobei der Ionisationsgrad der Anthocyane (a) bis zu 10fach schwanken konnte. Positive Qualitätsfaktoren waren: Farbintensität, der Parameter a, gefärbte Anthocyane, Gesamtpigmente sowie Gesamtphenole. Zu den negativen Faktoren gehörten Farbtönung, freies SO2 und Gesamt-SO2. Keinerlei Korrelation bestand zum Wein-pH. Die unterschiedlichen Qualitätsnoten der geprüften Rotweine dürften zum Gutteil kellertechnisch, durch die beträchtlichen Schwankungen der zugesetzten SO2 -Mengen und des Behandlungszeitpunktes, bedingt sein