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Composition of Sauvignon Blanc Grapes As Affected by Pre-Veraison Canopy Manipulation and Ripeness Level

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Composition of Sauvignon Blanc Grapes As Affected by Pre-Veraison Canopy Manipulation and Ripeness Level Composition of Sauvignon blanc Grapes as Affected by Pre-veraison Canopy Manipulation and Ripeness Level J.J. Hunter*, C.G. Volschenk, J. Marais and G.W. Fouche ARC Infruitec-Nietvoorbij, Private Bag X5026, 7599 Stellenbosch, South Africa Submitted for publication: June 2003 Accepted for publication: March 2004 Key words: Grapevine, Sauvignon blanc, canopy management, suckering, shoot positioning, topping, leaf thinning, yield, grape compo- sition, ripeness level The implications of pre-veraison canopy management and ripeness level (19°B and 21 °B) on microclimate and grape and must composition were determined on intensively micro-sprinkler irrigated Vitis vinifera L. cv. Sauvignon blanc/110 Richter vines, grown on a vertical trellis in the Breede River Valley of South Africa. Rows were y Canop . apart m c 5 1 y approximatel d space e wer s Spur . m 5 1. x m 5 2.7 d space s vine d an d orientate t east-wes management consisted of different combinations of seasonal practices (suckering, shoot positioning, topping, leaf thinning) during the pre-veraison growth period (just after budding to pea size berry) in order to accommodate foliage and to improve the canopy microclimate. Treatments that included leaf thinning improved the light conditions in the canopy without a noticeable effect on other microclimate parameters as well as bunch and berry sap temperature. The must pH remained relatively stable, with an increase in ripeness level from 19°B to 21°B, whereas the rest of the measured grape composition components followed a decreasing pattern during this period. Treatments that included leaf thinning tended to increase titratable acidity and decrease pH at both ripeness levels. Additional leaf thinning (up to the lower half of the canopy at pea size) increased the glucose and fructose concentrations without changing their ratio. It also decreased the malic acid concentrations of the berries, whereas the free-amino-nitrogen content of the must was stimulated. Furthermore, leaf thinning in general increased the monoterpene content (fruity aroma) and apparently enhanced the 2-methoxy-3-isobutylpyrazine content (grassy/green pepper aroma), thereby increasing the total measured aroma profile. Both palate and flavour profiles were therefore changed by applying pre-veraison seasonal canopy management. The data emphasised the importance of the correct timing and application of canopy management. This seemed to be of great significance in the realisation of an improved grape composition, even for S. blanc subjected to a relatively hot terroir. It is well known that macro/meso-climate affects grape composi- improved light distribution in the canopy. Judicious changing of tion and wine quality (Coombe, 1987, 1989). The sensitivity of the physical appearance of the canopy also has physiological the nitrogen-containing 2-methoxy-3-isobutylpyrazine (ibMP) implications that virtually always comprise a change in the compound, typically occurring in cultivars such as Sauvignon source:sink relationships in the grapevine and a simultaneous blanc, Cabernet Sauvignon and Semillon (Lacey et al., 1991) improvement in photosynthetic activity and export of photo- under conditions of high light intensity and/or high temperature, assimilates from leaves to sinks such as the berries (Johnson et has already been shown (Lacey et al., 1991; Alien & Lacey, 1993; al., 1982; Hunter & Visser, 1988a, 1988b, 1988c; Candolfi- Marais et al., 1999). The resulting reduction in grassy/green pep- Vasconcelos & Koblet, 1990; Hunter et al., 1995; Koblet et al., per-like aroma of the wine is a matter of concern to growers and 1996). Marrying the canopy microclimate required for the winemakers, particularly in the case of S. blanc. improvement of viticulturally-essential parameters - such as bud The value of canopy management for obtaining and improving burst, bud fertility, disease control, the accumulation of well- grape and wine quality in vineyards where it is required, because known quality-determining compounds (e.g. sugars, organic of injudicious long- and short-term decisions during establish- acids, amino acids, phenolics, monoterpenes) and berry pH with ment and cultivation, has been shown unequivocally (Kliewer et a sufficient, quality-contributing occurrence of typical character al., 1988; Koblet, 1988; Candolfi-Vasconcelos & Koblet, 1990; in the grapes of particularly S. blanc remains a challenge under Smart et al, 1990; Stapleton & Grant, 1992; Hunter et al., 1995; different environmental and cultivation conditions. Hunter, 2000; Volschenk & Hunter, 2001a, 2001b). Since canopy In this study the effect of judicious canopy management as well management (along with pruning, training and trellising) is pri- as ripeness level on the presence of some flavour- and palate- marily focused on altering canopy components (shoot position determining compounds in S. blanc grapes produced in a rela- and orientation), the microclimate that the grapes are subjected to tively hot terroir was investigated. The study was also aimed at during development is also changed, mostly in favour of elucidating the importance of creating improved metabolic func- *Corresponding author: E-mail address: [email protected] Acknowledgements: D.J. le Roux, E. Fourie, L.F. Adams, W.J. Hendricks and Personnel of the Robertson Experiment Farm for technical assistance and the South African vine and wine industry (through Winetech) for financial support. S. Afr. J. Enol. Vitic., Vol. 25, No. 1, 2004 13 14 Sauvignon blanc Grape Composition pre-veraisoe th g . durin nperiod s grape d an s leave tionin e th f go s ("Balling)solid H ,s g/p titratabl(a Ld y tartarian ) eacidit cacid Indicationg s are thaconsistin e t eventsampl s durinh bunc g e this period marepresentativ a y bm e criticafro d l in the determine e wer determination of eventual grape and wine qualit. y (Carbonneabunches n seve u t & leas t a f o Deloire, 2001; Hunter & Archer, 2001, 2002; Ojeda et al., 2002). Malic, tartaric and citric acid as well as glucose and fructose S METHOD D AN S MATERIAL s a d performe e wer C HPL y b s analyse d an s berrie m fro n extractio viticulturad s an d lpractice Vineyar described by Hunter et al. (1991). Grape monoterpene and ibMP n d VitisSauvigno vinifera. cv 10-year-ol . L s vigorou y visuall A extractions and analyses by means of GC and GC-MS were done blanc (clone SB 10) vineyard- , monoter grafte l d ontindividua oe 110 RichteRelativ . r (clon(1996) Maraio t g al. eset accordin et s Marai y b d describe s a d summarise e wer s concentration e pen RQ28A), and situated in the Robertson region (semi-arid Breede g (1999)al. accordin d . Free-amino-nitrogedetermine s wa ) n(FAN River Valley of the Western Cape - Winkler Region IV) (Hunter - refer s a e sulphat m ammoniu g usin d metho r Analyse o Aut n a o t g Workin n Classificatio l Bonnardot Huttoa & (Soi n l o ) nsoi ,2002 Group, 1991) was used. Vine rows were orientated approximate- ence (Anonymous, 1974). n cordo d an m 5 1. x m 5 2.7 d space , south-west o t t north-eas y l Statistical layout and analyses trained to a Lengthened Perold (Vertical Shoot Positioned) Treatments were replicated five times with five vines per replicate System (Zeeman, 1981). Two-bud spurs were spaced 15 cm apart. in a randomised block design and applied for three years. Buffer Intensiv. e micro-sprinklelayout l r irrigatioexperimenta e th n ni wad s appliedinclude t no . e wer s vine d an s row Treatments Mean values of the last two years of the experiment (1994/95 and Three treatments comprising different combinations of seasonal 1995/96) are presented. Student's t-LSD test was used to deter- ) suckering1 : t shoo ,applied e wer s practice t managemen y canop . differences t significan e min f lea , topping , positioning t shoo , suckering ) 2 ; topping , positioning RESULTS AND DISCUSSION f lea , topping , positioning t shoo , suckering ) 3 ; set y berr t a g thinnin thinning f lea d include t tha s treatment t managemen y Canop thinning at berry set and pea size. Treatments were harvested at , this f o e spit n I . 1) e (Tabl y canop e th n i s condition t ligh d increase ripeness levels of 19°B and 21°B, respectively. Shoot positioning other microclimate parameters (temperature, relative humidity, - correspond h wit e lin n i s shoot f o g positionin l vertica f o d consiste air flow) as well as bunch and berry sap temperature were large- ing spurs. Suckering consisted of the removal of shoots not located t tha y canop a n i d resulte g thinnin f lea m rando e Th . unaffected y l on spurs at approximately 30 cm main shoot length. Topping (30 s leave r interio e th t tha y wa a h suc n i e penetrat o t t sunligh d allowe cm above the top wire) was done twice during the period berry set and bunches received diffused (filtered) sunlight, which was , shoots f o m c 0 3 o t p u f o l remova e th d entaile d an e siz a pe o t recognised in the vineyard by the canopy shadow having small, resulting in a remaining primary shoot length of approximately 1.4 . 1990a) , Visser & r (Hunte s sun-fleck d distribute y evenl e th n i e sid o t e sid m fro y evenl e don s wa ) (33% g thinnin f Lea . m canopy on all leaves, i.e. on primary and secondary shoot leaves Average yield and bunch rot amounted to 15.8 ton/ha and 0.6%, d consiste g thinnin g durin d remove s leave f o % 30 y (approximatel .
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