Comparison of Ethanol and Acetone Mixtures for Extraction of Condensed Tannin from Grape Skin

Discrepancies in condensed tannin concentrations in grape skin determined by different analytical methodsprompted the closer examination of aspects of the methodologies. One of these was the choice of extraction solvent.Condensed tannins were extracted from Shiraz grape skins using a range of aqueous solvent mixtures ranging fromzero to 100% acetone and ethanol to examine the relative effectiveness of each solvent mixture and to determinewhether different solvent mixtures extracted similar condensed tannin components. Acetone extracted morecondensed tannin than ethanol. Mixtures of 50 to 70% acetone were equally effective. The most effective ethanolconcentration was 50%. Epicatechin-gallate terminal subunits were not detected by HPLC following acid-catalysedcleavage in any of the extraction solvents. Extension subunit composition was similar between solvents across mostmixtures. Polymers were generally shorter in the ethanol extracts than in the acetone extracts. Despite differencesin tannin concentration and polymer length, the subunit composition was similar in 50% ethanol and 70% acetone.More tannin and tannins with longer polymer lengths were extracted with 70% acetone than with 50% ethanol. Thissuggests that all grape skin tannins are similar in composition, varying only in length. Thus, 50% ethanol and 70%acetone would give a fair indication of the grape skin tannin composition extracted into wine. However, both 50%ethanol and 70% acetone may overestimate the amount of tannin that is extracted into wine, as wine typically has amuch lower solvent concentration, ranging between 10 and 15% ethanol

Resilience of Sultana (Vitis Vinifera) to Drought and Subsequent Recovery: Field Evaluation of Nine Rootstock Scion Combinations

The work reported here surveyed the recovery of H4 Sultana from severe drought when grafted to 9 rootstocks (101-14 Millardet, 116-60 Lider, 187-24 Lider, 5BB Kober, 1103 Paulsen, Ramsey, 140 Ruggeri, Schwarzmann and selfgraftedSultana). Vines did not receive any irrigation water from July until late February in the 2007 to 2008 seasonbut were watered normally thereafter to facilitate their recovery. Large differences in leaf retention and fruit yieldwere apparent among rootstocks just before rewatering and were quantified in order to document the influenceof rootstock on vine resilience and the potential for subsequent recovery. Vines grafted to the rootstocks 101-14Millardet, Schwarzmann and self-grafted Sultana performed poorly during drought and some vines did not recoverafter re-watering. Vines on other rootstocks retained a viable leaf canopy and showed good potential for recovery.Vines grafted to 187-24 Lider performed best showing high resilience during and good recovery from drought

Chemical Removal of Cordon Bunches in Dried Grape Production

The Shaw swing-arm trellis has increased mechanisation in dried grape production as it enables trellisdrying of the grapes in the vineyard. However, cordon bunches that do not dry reduce the quality of driedfruit at harvest. Traditionally, foliar application of ammonium nitrate was used to remove cordon bunches,but results were inconsistent. In recent years, health and safety concerns have heavily restricted the useof ammonium nitrate in the agricultural sector. Use of alternate chemical treatments was investigated tofind an alternative to ammonium nitrate for removal of cordon bunches in Carina Currant, Sultana andSunmuscat dried grape production. Different doses of calcium nitrate and Ethrel® (21.7%, w/v, ethephon)were applied to grapevines at various stages of vine growth. Calcium nitrate applied at a rate of 2.6%(w/v) to the vine pre-bloom at the 6 to 8 leaf stage (LS) and 250 ppm Ethrel® applied at full bloom (10 to 12LS) achieved the most effective results. Both treatments provide a cost effective alternative to ammoniumnitrate without any significant negative impact on growth, fruit bearing of vines and yield in the followingyear. Separate application scheduling of calcium nitrate (at pre-bloom) and Ethrel® (at full-bloom) offersflexibility in spray (application) schedules a management practices

Impact of exogenous tannin additions on wine chemistry and wine sensory character

Tannins are an important part of wine quality and are frequently added during winemaking. Tannin additives and their impact on wine are poorly documented. This work sought to characterize a range of enological tannins and their contribution to wine quality. Enological tannins were analysed for protein precipitable tannins and iron reactive phenolics. One tannin product was added to a Merlot wine during barrel ageing, at a range of concentrations from 60 to 300 mg/l. Condensed and hydrolysable tannins were added to Cabernet Sauvignon wine post-pressing at a recommended and excessive rate. Wines were analysed for anthocyanin, small and large polymeric pigment, precipitable tannin, iron reactive phenolics and sensory character. Enological tannins contained 12\u201348% tannin and recommended additions had little impact on wine tannin. High tannin additions were readily measured in the wines and were discriminated in sensory analysis with lower intensities of most parameters except brown colour, bitterness and earthy character. Recommended addition rates are too low to impact the measured tannin concentration of Merlot and Cabernet Sauvignon wines from Washington (USA). High enological tannin additions had a measureable impact on final wine had a negative impact on sensory character. Tannins are added to wines for a range of reasons and represent one of many input costs in an industry increasingly seeking efficiencies in response to global economic circumstances, over-supply and an ongoing price point squeeze. This research suggests many tannin additions may be unjustified and have limited or negative impacts on quality

Defoliation of two-wire vertical trellis: effect on grape quality

Basal leaves were removed from Cabernet Sauvignon vines trained to a two-wire vertical trellis at fruit set and at veraison. Leaf removal did not modify total soluble solids and titratable acidity at harvest. Defoliation at fruit set of lower cordon recovered the grape anthocyanin composition gap between upper and lower cordons and that produced a positive effect on anthocyanin synthesis. Hence, control of the upper cordon and defoliation of fruit set of the lower cordon treatments showed comparable values of anthocyanins. Defoliation at veraison did not produce any appreciable effect. This study shows that skin anthocyanin composition in a two-wire vertical trellis can be modified by leaf removal in the fruit zone of the lower cordon, reducing variability in the ripeness between the two cordons

Exclusion of sunlight from Shiraz grapes alters wine colour tannin and sensory properties

© 2008 Australian Wine Research Institute The definitive version may be found at www.wiley.comThe aim of this study was to determine how changes in grape composition brought about by artificial shading (sunlight exclusion) influence wine properties including colour, flavonoid composition and sensory attributes. Prior to flowering, bunches of Shiraz grapes were enclosed in boxes designed to eliminate light without altering bunch temperature and humidity. This artificial bunch shading had little effect on berry ripening and accumulation of sugar but at harvest the shaded bunches had smaller berries and higher seed weight, juice pH and titratable acidity. The amount of anthocyanins in the fruit was not changed significantly but anthocyanin composition in the shaded berries was shifted towards dioxygenated anthocyanins (the glucosides of cyanidin and peonidin derivatives). Shaded fruit had increased seed tannins and decreased skin tannins but the largest relative change in flavonoids was a marked decrease in flavonols in the shaded fruit, similar to previous studies. Wines made from shaded fruit had lower wine colour density, total phenolics, anthocyanins and tannins when the wine was bottled and after ageing for up to three years. Analysis of potential flavour compounds following acid hydrolysis indicated that the wines made from shaded fruit had decreased levels of glycosides of β-damascenone and 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN). Sensory analysis of the wines indicated no significant difference in aroma attributes but the wines made from shaded fruit were rated lower for astringency, fruit flavour and flavour persistence in-mouth sensory attributes. The results indicate that extreme shading of Shiraz fruit can decrease wine colour, anthocyanins and tannins as well as altering sensory attributes

Transcriptional regulation of anthocyanin biosynthesis in ripening fruits of grapevine under seasonal water deficit

Anthocyanin biosynthesis is strongly up-regulated in ripening fruit of grapevines (Vitis vinifera L.) grown under drought conditions. We investigated the effects of long-term water deficit on the expression of genes coding for flavonoid and anthocyanin biosynthetic enzymes and related transcription factors, genes sensitive to endogenous [sugars, abscisic acid (ABA)] and environmental (light) stimuli connected to drought stress, and genes developmentally regulated in ripening berries. Total anthocyanin content has increased at harvest in water-stressed (WS) fruits by 37-57% in two consecutive years. At least 84% of the total variation in anthocyanin content was explained by the linear relationship between the integral of mRNA accumulation of the specific anthocyanin biosynthetic gene UDP-glucose : flavonoid 3-O-glucosyltransferase (UFGT) and metabolite content during time series from v\ue9raison through ripening. Chalcone synthase (CHS2, CHS3) and flavanone 3-hydroxylase (F3H) genes of the flavonoid pathway showed high correlation as well. Genes coding for flavonoid 3\u2032,5\u2032-hydroxylase (F3\u20325\u2032H) and O-methyltransferase (OMT) were also up-regulated in berries from dehydrated plants in which anthocyanin composition enriched in more hydroxylated and more methoxylated derivatives such as malvidin and peonidin, the grape anthocyanins to which human gastric bilitranslocase displays the highest affinity. The induction in WS plants of structural and regulatory genes of the flavonoid pathway and of genes that trigger brassinosteroid hormonal onset of maturation suggested that the interrelationships between developmental and environmental signalling pathways were magnified by water deficit which actively promoted fruit maturation and, in this context, anthocyanin biosynthesis. \ua9 2007 The Authors