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Canopy Microclimate Modification for the Cultivar Shiraz II. Effects on Must and Wine Composition

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Canopy Microclimate Modification for the Cultivar Shiraz II. Effects on Must and Wine Composition Vitis 24, 119-128 (1985) Roseworthy Agricultural College, Roseworth y, South Australia South Australian Department of Agriculture, Adelaide, South Austraha Canopy microclimate modification for the cultivar Shiraz II. Effects on must and wine composition by R. E. SMART!), J. B. ROBINSON, G. R. DUE and c. J. BRIEN Veränderungen des Mikroklimas der Laubwand bei der Rebsorte Shiraz II. Beeinflussung der Most- und Weinzusammensetzung Z u sam menfa ss u n g : Bei der Rebsorte Shiraz wurde das Ausmaß der Beschattung innerha lb der Laubwand künstlich durch vier Behandlungsformen sowie natürlicherweise durch e ine n Wachstumsgradienten variiert. Beschattung bewirkte in den Traubenmosten eine Erniedri­ gung de r Zuckergehalte und eine Erhöhung der Malat- und K-Konzentrationen sowie der pH-Werte. Die Weine dieser Moste wiesen ebenfalls höhere pH- und K-Werte sowie einen venin­ gerten Anteil ionisierter Anthocyane auf. Statistische Berechnungen ergaben positive Korrelatio­ nen zwischen hohen pH- und K-Werten in Most und Wein einerseits u11d der Beschattung der Laubwand andererseits; die Farbintensität sowie die Konzentrationen der gesamten und ionisier­ ten Anthocyane und der Phenole waren mit der Beschattung negativ korreliert. Zur Beschreibung der Lichtverhältnisse in der Laubwand wurde ei11 Bonitierungsschema, das sich auf acht Merkmale stützt, verwendet; die hiermit gewonne nen Ergebnisse korrelierten mit Zucker, pH- und K-Werten des Mostes sowie mit pH, Säure, K, Farbintensität, gesamten und ionj­ sierten Anthocyanen und Phenolen des Weines. Starkwüchsige Reben lieferten ähnliche Werte der Most- und Weinzusammensetzung wie solche mit künstlicher Beschattung. K e y wo r d s : climate, light, growth, must quality, wine quality, malic acid, potassium, aci­ dity, anthocyanjn. Introduction This paper is a companion to that by SMART et al. (1985), which described the effect of canopy manipulation on the radiation microclimate. Now the effects of microclimate change on must and wine composition are investigated. The previous paper proposed that the effects of soil, climate and cultural practice on must composition and wine quality could be understood, at least in part, by recog­ nising the effect of these factors on canopy microclimate. A number of factors can cause stimulation of grapevine vigour and concomitantly yield, and unless there are changes made to the training system, increased within-can­ opy shading can be the consequence. Given that shading reduces wine quality as is demonstrated here, we believe that considering microclimate leads to an explanation of the common observation that high yields lead to reduced quality. Recent studies have demonstrated an effect of canopy microclimate on must com­ position and wine quality (CARBONN EAU and HuGLI N 1982; SMART 1982). Common quality defects for Australian dry red table wines are high pH and low colour and phenol con­ tent (SoMERS 1975). The present study was designed to investigate whether a shaded 1) Present address: Ruakura Soil and Plant Research Station, Hamilton, New Zealand. 120 R. E. SMART, J. B. ROBINSON, G. R. DUE and c. J . BRJEN canopy microclimate is associated with these problems. Four different methods of managing grapevine canopies were studied, as weil as a naturally occurring variation in vine vigour, for effects on microclimate and must and wine composition. Further­ more, a system of visually assessing grapevine canopies was evaluated for association with must and wine composition. Materialsand methods 1 . Vineyard treatments Full details of the experimental site are given by SMART et al. 1985. Four treatments were used to provide a range of canopy microclimates: T r e a t m e n t 1 - s h a d e ( T 1 ) : The vine foliage was constrained into a smaller volume using a thin filament bird netting. This produced a very shaded micro­ climate. Treatment 2 s l a s h ( T 2 ) : Shoots were trimmed to about 9 nodes per shoot. Treatment3 c o n t r o l ( T 3 ) : The canopies grew in the normal growth habit. T r e a t m e n t 4 G D C ( T 4 ) : The vines were trained to Geneva double cur- tain with proper shoot positioning as described by SHAULIS et al. 1966. There were nine replicates of each treatment. The blocks were arranged across a pronounced vigour measurement, with block 9 plots the most vigorous, and block 1 the least. The companion paper, SMART et al. 1985, outlined viticultural and microclimate measurements. 2. Fruit and wine measurements 50 berry samples were taken from each plot during ripening (9 February and 24 February). Juice was separated by pressing berries against a fine screen and then centrifuging before sugar, acid and pH determination. Samples diluted 1 : 1 were frozen for subsequent K and organic acid analysis. The fruit from each plot was processed into wine using a procedure described by SMART (1982). Yields ranged from 7.4 to 30.5 kg/vine, with an average of 17.l k g. Each must was adjusted to 7 g/l titratable acidity at the onset of fermentation. Many of the wines produced H2S during fermentation which was treated with up to 3 ppm Cu2+ prior to bottling. Organic acid analyses were made with HPLC and cation concentrations by flame photometry. The spectral measurements due to SOMERS and EVANS (1977) were used. Sensory evaluation was carried out on 20 October 1981, by six experienced enolo­ gists from the Australian wine industry. Ten different wines were presented to each judge in each of four sessions. Within each session, at least two w ines were repeated to allow assessment of the judge's performance. The other eight wines consisted of two replicates of four treatments. Wines from replicate one were not subjected to evalua­ tion due to presence of H2S . Wines were scored with standard Australian Wine Show system (3 points for colour, 7 points for bouquet and aroma and 10 points for palate). Subjective ratings were also given for colour density and hue, and fruit flavour on the palate and nose (ex 5 points). Taster reliability was evaluated by performing an analysis of variance on the pairs of scores for the eleven dup!icated wines. The intraclass correlation coefficient was cal­ culated as a me~sure of reliability. Canopy microclimate modification for the cultivar Shirai. II. 121 Results 1. Fruit composition Changes in fruit composition during ripening are shown in Table 1. Delayed maturity was evident for Tl shade, T2 s.lash and T4 GDC early in the period, but at har­ vest there was no significant difference. Juice.K concentration and pH were lower for T4 GDC over the period, the highest for Tl shade. Malic acid levels were highest for Tl shade at 24 February. Replicate effects were significant o n 1 y for sugar concentra­ tion, being highest on the low vigour plots. Table 1 Changes in fruit composition during ripening Die Veränderung der Beerenzusammensetzung während des Reifeverlaufes Treatment Variable Tl shade T2 slash T3 control T4GDC 5 0/o LSD 9 February Sugar (0 Brix) 15.2 17 .2 18.5 16.6 1.3 Titratable acidity (g/l) 10.l 9.1 8.3 10.4 0.6 pH 3.16 3.13 3.21 3.05 0.03 K(ppm) 1 760 1 840 1 770 1 730 NS Tartaric acid (g/1) 7.8 7.8 7.3 7.8 NS Malic acid (g/l) 4.5 3.8 3.6 4.6 NS 24 February Sugar (0 Brix) 18.5 20.2 21.3 19.5 1.0 Titratable acidity (g/l) 7.1 6.4 6.1 6.7 0.5 pH 3.54 3.44 3.54 3.36 0.04 K(ppm) 2 220 1 960 2 310 1 920 180 Tartaric acid (g/1) 6.4 . 7.0 7.3 7.2 NS Malic acid (g/l) 4.1 2.3 2.5 2.9 0.6 19 March (harvest) Sugar (0 Brix) 22.l 23".0 23.5 23.6 NS Titratable acidity (g/l) 4.2 3.9 3.8 3.8 NS pH 3.89 3.82 3.80 3.67 NS K(ppm) 1 930 1 780 1 780 1 502 170 NS ~ Not significant. 2. Wine composition Wine composition analyses, presented in Table 2, show that T4 GDC had generally the most desirable composition and Tl shade the least desirable. In particular, wines from Tl shade had lowest titratable acidity and tartaric acid, highest pH and K and succinic acid content, and lowest colour density, proportion of ionised anthocyanin, total and ionised anthocyanins and total phenols, and highest colour hue. Not all of these analyses reached significance at the 5 % level but the trends were consistent. 122 R. E. SMART, J. B. ROBI NSON, G. R: DUE and c. J. BRIEN Table 2 Effects of treatment on wine composition Der Einfluß der Behandlung auf die Weinzusammensetzung Treatment Variable Tl shade T2 slash T3 control T4GDC 5 % LSD Titratable acidity (g/l) 7.0 7.6 7.4 8.3 0.4 pH 3.62 3.46 3.54 3.35 0.09 K(ppm) 1 700 1 470 1 580 1 270 130 Tartaric acid (g/l) 2.24 2.44 2.28 2.91 0.16 Lactic acid (g/1) 0.82 0.75 0.71 0.83 0.047 Succinic acid (g/1) 0.23 0.18 0.22 0.15 0.029 Wine colour densityI) 8.6 11.8 12.6 12.2 NS Wine colour hue1) 0.54 0.48 0.49 0.45 NS a (%)') 24.7 31.7 29.l 34.0 3.6 a' (%)') 27.3 33.9 31.7 37.8 2.8 Total anthocyanins (mg/l)I) 340 371 437 405 NS Ionised anthocyanins (mg/1)1) 86 122 129 136 NS Total phenols 33.9 38.5 43.3 41.3 NS ') After techniques of Sm1ERS and EvANS (1977).
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