Wine Colour Density Research Articles

Non-acylated and acylated anthocynins in red wines of different ages: Color contribution and evaluation

This study investigated the non-acylated and acylated anthocyanins and chromatic characteristics of 108 red wines with a range of ages. The K-means cluster analysis showed that the evolution pattern of cyanidin-3-O-glucoside (Cy) differed among non-acylated anthocyanins and the pattern of malvidin-3-O-(6-O-acetyl)-glucoside (Mv-ac) differed among acylated anthocyanins. Partial least squares regression (PLS) showed that non-acylated anthocyanins, especially Cy, contributed to the red-violet color. Wine age, tawny characteristics, and color density strongly negatively correlated with anthocyanins. Wine age played an essential role in chromatic characteristics and anthocyanins, especially more than 4 years. A prediction model of wine age was established using the chosen variables of color parameters and anthocyanins employing PLS. This model showed good performance in predicting the wine age. Besides malvidin-3-O-glucoside (Mv), other anthocyanins and acylated forms with low content were demonstrated to be promising and practical chemical parameters for predicting the age of dry red wine.

Phenolic contents, antioxidant activity and colour density of Slovak Pinot Noir wines

Recent studies show that wine contains more than thousand different compounds that could come from grapes, or could be formed in the process of winemaking and maturing. The most abundant compounds in wines are polyphenols, which affect sensory properties such as colour, taste and aroma, but also has antioxidant properties. The aim of this study was to determine total polyphenol and total anthocyanin contents, and to evaluate antioxidant effects and wine colour density of red wines ‘Pinot Noir’ produced in Slovakia. Thirteen analysed, bottled, quality dry ‘Pinot Noir’ wines with origin in various Slovak wine regions were purchased in retail network, to provide that analysed samples of wine would have the same properties as wines that are consumed by common consumers. The content of total polyphenols in analysed ‘Pinot Noir’ wines ranged from 1458 to 3324 mg GAE l-1, while contents of total anthocyanins ranged from 43.6 to 279.6 mg l-1. Antioxidant activities ranged from 80.2 % to 85.3 % inhibition of DPPH and wine colour density ranged from 0.679 to 1.495. The highest total polyphenol content, total anthocyanin content, and wine colour density was determined in wines from the south Slovakia winegrowing region, while the highest antioxidant activity in wines from Nitra winegrowing region. Results did not show significant differences among studied parameters in wines from different winegrowing regions. Results showed that Slovakian ‘Pinot Noir’ wines have characteristics comparable with ‘Pinot Noir’ wines from other countries.

Comparison of water addition and early‐harvest strategies to decrease alcohol concentration inVitis viniferacv. Shiraz wine: impact on wine phenolics, tannin composition and colour properties

Background and Aims Regulations in some wine‐producing countries allow water addition to grape must. The research presented compared the impact of water addition to must on wine phenolics and colour relative to that of wines at the same alcohol concentration, prepared from fruit harvested earlier. Methods and Results Shiraz grapes were harvested at three stages; earlier harvest at 13.4 and 14.4°Be (H‐1, H‐2) and a later harvest at 15.6°Be (H‐3). Water was then added to H‐3 must to match the sugar concentration of H‐1 and H‐2, respectively. Two modes of water addition were followed: (i) water was directly added to the must; or (ii) juice was substituted for water. Both water addition treatments significantly decreased the concentration of phenolics throughout the winemaking process. At the end of malolactic fermentation, the concentration of phenolics, tannin and non‐bleachable pigments, tannin molecular mass and wine colour density were lower in the water addition treatments compared with that of H‐3, but in all other compositional aspects were higher than that of H‐1 and H‐2. Interestingly, where the extent of alcohol reduction by water addition was equivalent, no difference in any of the measured wine attributes was found between the two modes of water addition. Conclusions Water addition to the H‐3 treatment led to higher wine tannin, colour and non‐bleachable pigment than were found in wines made from grapes harvested at a lower sugar concentration. Significance of the Study The study presents a meaningful comparison of potential outcomes in Shiraz wine phenolics and colour for producers who aim to lower alcohol using the approaches of either water addition or early harvest.

Effect of rootstock on yield, grape composition and wine sensory attributes of Shiraz grown in a moderately saline environment

Background and Aims The study compared the viticultural performance and wine sensory attributes of Shiraz grafted on eight rootstocks with a range in vine vigour and grown under drip-irrigation with moderately saline water. Methods and Results The rootstocks were 140 Ruggeri, 1103 Paulsen, 110 Richter, Ramsey, 101-14, M5489, M5512 and M6262. Ramsey and 140 Ruggeri had the highest leaf area index and M6262 the lowest. Ramsey had highest yield, followed by 140 Ruggeri > M5489 = 110 Richter > M5512 > 1103 Paulsen = 101-14 > M6262. Rootstock M6262 had highest wine chloride concentration of 482 and 384 mg/L in 2012 and 2013, respectively, but salty taste and a thickness mouthfeel (viscosity) were significant only in 2012. Wines from the other seven rootstocks had a chloride and sodium concentration under 175 and 40 mg/L, respectively. Colour density was highest in wine from 101-14 in 2012 and from 101-14, 1103 Paulsen and M5489 in 2013. A salt tolerance index (STI) for the eight rootstocks was calculated based on yield, leaf area index, grape juice chloride and sodium concentration and wine colour density. Conclusions Rootstock M6262 had lowest STI in both years. M5489 had highest STI in 2013 followed by 110 Richter = M5512 = 101-14 = 140 Ruggeri. The recognition threshold for salty taste may lie between a chloride concentration in wine of between 384 and 482 mg/L. Significance of the Study The STI, based on five wine grape performance parameters, provides a promising measure of rootstock salt tolerance compared with the traditional parameters of yield and/or capacity for salt exclusion.

Late pruning impacts on chemical and sensory attributes of Shiraz wine

Background and Aims Warming has two major effects on the wine industry: compressing harvest duration, thus stressing the current capacity of wineries to process more fruit in a shorter time, and compromising fruit composition and wine style. Late pruning can effectively delay vine development and contribute to decompressing harvest, but its impact on wine is unknown. Our aim was to measure the effects of late pruning on wine chemical and sensory attributes. Methods and Results We compared wines made from Shiraz vines pruned in winter (Control), and in two late pruning stages, when Controls reached budburst and 2–3 leaves in two vintages. Late pruning consistently increased wine anthocyanin, tannin, pigmented tannin and colour density and altered the wine's sensory profiles over two vintages. In 2014, colour intensity, fruit aroma, fruit flavours and body were more intense in wine made from late pruning treatments. In 2015, wine made from late pruning treatments showed more intense savoury flavours with a dryer palate and a smoother texture tannin (roughing sub-quality). The colour improvement was associated with cooler temperature 1 week after veraison in the late-pruned vines. Conclusions Late pruning consistently improved wine chemical composition and altered sensory profiles of Shiraz under Barossa Valley conditions. Significance of the Study Late pruning is a cost-effective tool to decompress harvest, with neutral effects on yield and positive effects on wine chemical attributes with enhancement of fruit and colour intensity perception in an extended vintage (2014), and smoother tannin texture with dryer perception in a short and compressed vintage (2015).

Pinot noir Wine Processing and Quality Improved by Skin Fragmentation

Summary Goals: During vintage 2013, the option of using fragmented grape skins for Accentuated Cut Edges (ACE) maceration to improve the phenolic profile of Pinot noir was evaluated at commercial wineries. Subsequently, a small-scale vinification trial was conducted in 2014 to determine whether the enhanced extraction of grape skin components during the first few days of ACE treatment was sufficient to allow grape solids to be pressed from the fermenting wine early, without compromising wine quality. In the following year, commercial trials were conducted to appraise processing efficiency and quality parameters for ACE and Pressed Early Accentuated Cut Edge (PEACE) treated wines. Key Findings: Commercial evaluation of the ACE maceration technique showed improvement in wine color density and stable pigment compared to conventionally made wine. Small-scale and commercial vinification demonstrated substantial benefits when ACE-treated wines were pressed early to make PEACE wines. Discriminative analyses showed clear sensory differences between conventional, ACE, and PEACE-treated wines: the tasting panel preferred ACE and PEACE for color, fruit characters, and structure. Participants at an international tasting workshop favored the PEACE and ACE wines over conventionally made wine by a ratio of six to one. Impact and Significance: Commercial evaluation of ACE maceration and its refinement, PEACE maceration, confirmed that these two new techniques are viable and important winemaking options for the commercial sector, with the potential to reduce processing time and space and labor requirements in the winery. Sensory properties of wines made using ACE and PEACE techniques were found to be favorable, with phenolic quality parameters maintained or improved relative to conventional treatments.

Effect of water deficits and season on berry development and composition of Cabernet Sauvignon (Vitis viniferaL.) grown in a hot climate

Background and Aims The effect of season and deficit irrigation treatments was monitored on berry development and composition, yield and wine composition of Vitis vinifera L. cv. Cabernet Sauvignon grown in a hot climate during 2003–2005. Methods and Results The treatments were regulated deficit irrigation (RDI) and prolonged deficit irrigation (PD), compared with a standard industry irrigation (Control) treatment. Compared to the Control, RDI berries were smaller from a reduction in mesocarp (flesh) rather than in exocarp (skin) or seed mass but insufficient to significantly impact on yield. The PD treatment reduced berry size driven by mesocarp reduction resulting in a lower yield. Season 2005 had a significantly larger yield, mainly as a result of increased berry fresh mass, exocarp and seed mass compared to that of either 2003 or 2004. Grape juice TSS and pH were not significantly affected by water deficit, but each varied between seasons. The malic acid concentration of grape juice was reduced by the RDI and PD treatments, resulting in enhancement of the tartaric : malic acid ratio. Grape anthocyanin at harvest was unaffected by irrigation treatment but significantly impacted by season. Wine colour density, anthocyanin, ionised anthocyanin and phenolic substances were increased by RDI and PD and impacted by season. Conclusions Wine attributes were improved further by PD relative to RDI. Seasonal effects were shown to have an impact greater than the within-season water deficit treatments on most aspects of berry development and composition. Significance of the Study The study has demonstrated the utility of the PD treatment as an irrigation tool, where water availability is significantly limited and/or where improved spectral properties are required for wines.

Response of Grape and Wine Phenolic Composition in Vitis vinifera L. cv. Merlot to Variation in Grapevine Water Status

Grape and wine phenolic composition was monitored over two consecutive seasons in Vitis vinifera cv. Merlot following application of irrigation treatments that produced seasonal average stem water potentials ranging between -0.7 MPa and -1.4 MPa. Fresh weight of berries was significantly reduced in response to water deficit, primarily due to decreases in pericarp weight. Increases in the concentration of grape anthocyanins and flavonols in response to water deficit were found when expressed per unit grape berry fresh weight. Skin-derived tannin concentration in grape berries was not affected by the irrigation treatments. The concentration of grapederived phenolics was monitored during five days of fermentation in a small-lot winemaking experiment. During fermentation, the concentration of anthocyanins and flavonols in wine were highest in the non-irrigated and lowfrequency- irrigated treatments, which was reflected in changes in the wine colour of ferments. Finished wines from non-irrigated and low frequency irrigated grapevines showed increases in bisulphite-resistant pigments when compared with those irrigated at a high frequency, but differences in phenolic composition were minor. Increases in bisulphite-resistant pigments were associated with increases in vitisin A and polymeric pigment in the first and second seasons of the study respectively. Ageing of wines for an 18-month period increased bisulphite-resistant pigments, and treatment differences in wine colour density were enhanced, such that increases in both parameters were associated with the non-irrigated and low-frequency-irrigated treatments.

Change of selected antioxidant parameters of red wines during maturation

The effects of red wine maturation on the contents of selected parameters of bioactive compounds in wine were determined. Samples of Alibernet, Cabernet Sauvignon, and Torysa wines were studied by spectrophotometric analysis after 3, 7, 11, 19, and 28 months of aging and the selected parameter content was statistically evaluated. Statistically highly significant changes in total polyphenol content, total anthocyanin content, antioxidant activity, and wine colour density were found depending on the aging according to the used statistical analyses. The obtained results can be used for the optimisation of the wine aging process and they allow producers to time the optimal date of wine release onto the market, depending on the desired content parameters.

Prediction of Phenolic Composition of Shiraz Wines Using Attenuated Total Reflectance Mid-Infrared (ATR-MIR) Spectroscopy

Phenolic compounds play a critical role in determining red wine color, taste, flavor, and mouthfeel sensory attributes. Additionally, they contribute to wine aging and provide wine stability. This study evaluated the use of an attenuated total reflection (ATR) mid-infrared (MIR) spectroscopy to measure phenolic compounds in Shiraz wine samples of different quality levels obtained from 24 Australian wine geographical indications. Partial least squares (PLS) regression using the second derivative of the whole MIR spectrum produced the coefficient of determination (R2) in calibration and standard error in cross-validation (SECV) for different attributes. In particular, SO2-resistant pigments had R2 = 0.58 (SECV=0.58 au), total anthocyanins had R2 = 0.61 (SECV=32 mg/L), wine color density had R2 = 0.51 (SECV=0.56 au), and total phenolics had R2 = 0.60 (SECV=5.7 au). These results demonstrated the potential use of ATR-MIR spectroscopy with PLS regression as a rapid method to measure important parameters related to red wine phenolic composition and wine quality.

Antioxidant activity, phenolic content and colour of the Slovak cabernet sauvignon wines

Antioxidants are specific substances that oxidize themselves and in this way they protect other sensitive bioactive food components against destruction. At the same time, they restrict the activity of free radicals and change them to less active forms. Grapes and wine are a significant source of antioxidants in human nutrition. One of the most important group occuring in grapes and wines are polyphenols. Many of phenolic compounds have been reported to have multiple biological activities, including cardioprotective, anti-inflammatory, anti-carcinogenic, antiviral and antibacterial properties attributed mainly to their antioxidant and antiradical activity. Therefore, it is important to know the content of polyphenols and their antioxidant effects in foods and beverages. Twenty-eight Cabernet Sauvignon wine samples, originated from different Slovak vineyard regions, were analyzed using spectrophotometry for the content of total polyphenols, content of total anthocyanins, antioxidant activity and wine colour density. Determined values of antioxidant activity in observed wines were within the interval 69.0 - 84.2% inhibition of DPPH (average value was 78.8% inhibition of DPPH) and total polyphenol content ranged from 1,218 to 3,444 mg gallic acid per liter (average content was 2,424 mg gallic acid.L-1). Determined total anthocyanin contents were from 68.6 to 430.7 mg.L-1 (average content was 220.6 mg.L-1) and values of wine colour density ranged from 0.756 to 2.782 (average value was 1.399). The statistical evaluation of the obtained results did not confirm any linear correlations between total polyphenol content, resp. total anthocyanin content and antioxidant activity. The correlations between total polyphenol content and total anthocyanin content, resp. the content of total anthocyanins and wine colour density were strong. The results confirmed very strong correlations between wine colour density and total polyphenol content, resp. antioxidant activity.

Effect of acetaldehyde addition on the phenolic substances and volatile compounds of red Tempranillo wines

Background and Aims The introduction of controlled amounts of oxygen into red wines influences the composition of the phenolic substances and volatiles, and therefore the sensory properties of the wines. The main aim of this study was to evaluate the impact of a simulation of the micro-oxygenation technique through acetaldehyde addition, on colour, and on the composition of phenolic substances and volatiles of Tempranillo wines after 12 months of bottle storage. Methods and Results The analytical and sensory data were subjected to ANOVA, principal component analysis and orthogonal projection in latent structures discriminant analysis. Addition of acetaldehyde led to an increase in the anthocyanin fraction in coloured form, thus increasing wine colour, together with a change in the composition of the volatiles. Acetaldehyde addition appeared to strongly impact wine ester composition, along with fatty acids and volatile phenols; furthermore, acetaldehyde addition positively influenced the concentration of volatiles. Conclusions Acetaldehyde addition to red wine caused an increase in the polymeric fraction of the phenolic substances with its corresponding effect on wine colour density and astringency index. Moreover, the volatiles fraction has been better protected during ageing in wines to which acetaldehyde has been added. The acetaldehyde treatment therefore led to a clear difference in the chemical composition of the wines. Significance of the Study An increase in acetaldehyde in red wines can lead to profound changes in the composition of phenolic substances and volatiles of the wines and may serve as an alternative to oxygen addition in red wines where oxidation is studied.

Skin Particle Size Affects the Phenolic Attributes of Pinot noir Wine: Proof of Concept

Modifying phenolic composition can improve the quality of Pinot noir wines and overcome common challenges associated with deficiencies in color, tannin, and aging potential. During fermentation, extraction of desirable components from the skin takes place primarily through the inner skin surface of the berry and from broken skin edges. Ostensibly, the extraction of phenolic compounds located in the skin may be enhanced by reducing the skin particle size. Theoretical analysis indicated that moderate fragmentation substantially decreased the surface area to perimeter ratio of grape skins. Three experiments showed that cutting grape skins into smaller fragments facilitated egress of color and tannin from the skin into the wine matrix. In each case, the treatment in which grapes were cut was compared with a crushed berry control made using conventional methods. Homogenization of berry tissues increased tannin concentration by 6-fold, stable pigment concentration by 45%, wine color density by 25%, and blue-purple coloration by 20% in wines at six months bottle age. Undifferentiated cutting of grapes increased tannin by 6.5-fold, stable pigment concentration by 70%, wine color density by 60%, and blue-purple coloration by 10%. A cutting technique that reduced grape skins to 6% of their original size without damaging the seeds produced wines that had 3-fold higher tannin concentration, 95% higher stable pigment concentration, 50% greater wine color density, and 20% increase in blue-purple coloration. The effects of reducing skin particle size on phenolic extraction were found to be much greater than those achieved using pectolytic enzymes. This innovative skin fragmentation technique has the potential to increase skin-derived red wine phenolics and is a viable alternative to maceration techniques currently used during winemaking.

COLOUR, PHENOLIC CONTENT AND ANTIOXIDANT ACTIVITY OF THE SLOVAK ALIBERNET RED WINE SAMPLES

Sixteen Alibernet wine samples, originated from three most important Slovak vineyard regions, were evaluated spectrophotometrically for the content of total polyphenols, content of total anthocyanins, antioxidant activity and wine colour density. The determined total polyphenol contents in observed wines ranged from 2141 to 4274 mg gallic acid per liter (average content was 3057 mg gallic acid/L) and total anthocyanin contents ranged from 73.4 to 791.2 mg/L (average content was 403.4 mg/L). Determined values of antioxidant activity were within the interval 54.8 – 86.8% (average value was 74.5%) and the values of wine colour density varied between 0.944 and 4.592 (average value was 2.317). The statistical evaluation of the obtained results confirmed only weak linear correlation between total polyphenol content and total anthocyanin content, however strong linear correlations between total anthocyanin content and antioxidant activity, resp. wine colour density were observed. Our results also confirmed very highly significant linear relationship between wine colour density and total polyphenol content, resp. antioxidant activity and between antioxidant activity and total phenolic content.

Effect of grape bunch sunlight exposure and UV radiation on phenolics and volatile composition of Vitis vinifera L. cv. Pinot noir wine

The effect of canopy leaf removal and ultraviolet (UV) on Pinot noir grape and wine composition was investigated in this study. Limited basal leaf removal in the fruit zone was conducted, compared to shaded bunches. The UV exposure was controlled using polycarbonate screens to block UV radiation, and acrylic screens to pass the UV. The results showed that bunch sunlight and UV exposure significantly increased the Brix and pH in the grape juice, and increased substantially wine colour density, anthocyanins, total pigment, total phenolics and tannin content. Bunch sunlight and UV exposure affected terpene alcohols, C13-norisprenoids and other volatile composition of the wine differently. Sunlight exposure and UV resulted in increase of nerol, geraniol and citronellol but not linalool. Sunlight exposure slightly increased the concentration of β-ionone, but the increase was not statistically significant for UV treatment. Neither sunlight nor UV treatment showed any impact on the concentration of β-damascenone.

Development of wine colour and non-bleachable pigments during the fermentation and ageing of (Vitis vinifera L. cv.) Cabernet Sauvignon wines differing in anthocyanin and tannin concentration

Non-bleachable (SO2-resistant) pigment formation in wine is related to the concentration of grape-derived anthocyanin and tannin, but their relative impact on the formation and composition of SO2-resistant pigments is poorly understood. Colour development during fermentation and ageing was analysed in two wines produced from grape batches with different anthocyanin and tannin concentrations. Higher anthocyanin and tannin concentrations extracted during fermentation were associated with increased wine colour density, total SO2-resistant pigments and SO2-resistant polymeric pigment. During ageing, wine colour density decreased, but differences between the respective wine treatments were retained. Wine tannin concentration was unchanged with age, anthocyanin decreased, and SO2-resistant pigments increased. Fractionation of wines indicated that SO2-resistant pigments in both polymeric and non-polymeric forms increased with ageing. Increases in tannin pigmentation over time were associated with decreased tannin molecular mass, reflecting the conversion of tannin to lower molecular mass pigmented polymers. The formation of polymeric pigment during ageing was related to the initial wine tannin concentration. However, non-polymeric forms of SO2-resistant pigments increased to a greater extent in wines with higher initial anthocyanin and tannin concentrations. The data suggests that both polymeric and low molecular mass anthocyanin derivatives are important for stable wine colour development.

Application of Insoluble Fibers in the Fining of Wine Phenolics

The application of animal-derived proteins as wine fining agents has been subject to increased regulation in recent years. As an alternative to protein-based fining agents, insoluble plant-derived fibers have the capacity to adsorb red wine tannins. Changes in red wine tannin were analyzed following application of fibers derived from apple and grape and protein-based fining agents. Other changes in wine composition, namely, color, monomeric phenolics, metals, and turbidity, were also determined. Wine tannin was maximally reduced by application of an apple pomace fiber and a grape pomace fiber (G4), removing 42 and 38%, respectively. Potassium caseinate maximally removed 19% of wine tannin, although applied at a lower dose. Fibers reduced anthocyanins, total phenolics, and wine color density, but changes in wine hue were minor. Proteins and apple fiber selectively removed high molecular mass phenolics, whereas grape fibers removed those of both high and low molecular mass. The results show that insoluble fibers may be considered as alternative fining agents for red wines.

Appraisal of wine color and phenols from a non-invasive grape berry fluorescence method

<p style="text-align: justify;"><strong>Aims</strong>: To investigate the relationships between the anthocyanin content of <em>Vitis vinifera</em> L. cvs. Tempranillo and Graciano grapes, determined in the vineyard and in the winery by a non-invasive fluorescence sensor, and the final wine color and phenolic traits.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Grape anthocyanin and phenol measurements were conducted with a hand-held, non-destructive fluorescence-based proximal sensor, in the vineyard (on clusters hanging on the vine) and at the winery (on harvested clusters in boxes) in two seasons. The anthocyanin fluorescence indices, ANTH_RG and FERARI, were found to significantly correlate with the wine color density (R<sup>2</sup> ranged from 0.51 to 0.82) and total phenol index (R<sup>2</sup> ranged from 0.44 to 0.87), regardless that the measurements were made in the vineyard or in the winery. Similarly, the CIELAB parameters defining lightness (L*), hue angle (h*) and coordinate b* (yellow-blue component of the wine tonality) also showed significant relationships (R<sup>2</sup> ranged from 0.55 to 0.74) with ANTH_RG and FERARI indices in very young wines.</p><p style="text-align: justify;"><strong>Conclusion</strong>: This preliminary study showed that satisfactory estimation of the final wine color and phenolic characteristics can be obtained from fast, non-destructive measurements in grapes, using a fluorescence-based sensor, either in the vineyard or in the winery.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: This is the first work showing the capabilities of the chlorophyll fluorescence of grapes to estimate the final wine color and phenolic traits. This information could help the wine industry make more informed decisions regarding selective harvest and winemaking in a fast and cost-effective way.</p>

MECHANICAL CROP THINNING AND EARLY DEFOLIATION AS NOVEL TOOLS FOR YIELD MANAGEMENT IN VSP GRAPEVINES

Cost-effective yield management is becoming fundamental in modern viticulture in order to meet the existing yield regulations in many parts of the world and to improve grape quality. The evaluation of mechanically performed early defoliation and crop thinning, aiming at yield management, and their effects on the vegetative growth, yield components, grape and wine composition, against a non-defoliated, not-thinned control, and manual treatments are presented. Manual and mechanical early defoliation and crop thinning were conducted at pre-bloom and veraison, respectively, on ‘Tempranillo’ (Vitis vinifera L.) VSP grapevines in season 2009. A detailed description of the mechanical settings and adjustments, based on preliminary results from previous seasons, for the correct performance of both techniques is provided. Whilst total leaf area remained unaltered, yield was drastically reduced by both practices (38-40%), hence the leaf-to-fruit ratio also enhanced with respect to control vines. Cluster weight, berry number, as well as cluster compactness and Botrytis incidence were also reduced in yield regulated vines, but berry weight tended to increase in mechanically thinned vines and remained unaffected in the early defoliated plants. Berry soluble solids, anthocyanins and total phenols, as well as wine alcohol, color density and total phenol index were generally higher in mechanically early defoliated vines. Effective yield control and fruit quality improvement in VSP grapevines may be accomplished mechanically.

Regulated Deficit Irrigation Effect on Yield and Wine Color of Cabernet Sauvignon in Central California

Regulated deficit irrigation (RDI) is a management strategy that on grape can improve shoot/fruit ratio, water efficiency, and wine quality but has the potential to reduce yield. As part of a study on the influence of RDI on leafhopper density, we evaluated the effects on grape yield, berry size, berry soluble solids, and wine color. The studies were conducted at commercial vineyards in the San Joaquin Valley and in the Paso Robles region, CA, with Cabernet Sauvignon as the cultivar. Water deficits were imposed at either 50% (moderate deficit) or 25% (severe deficit) of standard irrigation (the control) for a period of 3 or 6 weeks and initiated at berry set, leafhopper egg hatch, or veraison. Deficit irrigation decreased berry weight by 16.1% at the San Joaquin Valley site (Aliso) and 11.7% at one of the Paso Robles sites (Frankel) but did not differ at the other site (Steinbeck). Yield was decreased by the deficits by 18.1% at Aliso, 26.7% at Frankel 2001 (but not 2002), and 24% at Steinbeck. Wine color density was increased by 21.8% at Aliso, 34.4% at Frankel 2001 (but not 2002), and did not differ at Steinbeck. Soluble solids did not differ among treatments at any site. There was no difference in berry weight, yield, or color between the moderate and severe deficits. It appears that in central California, RDI such as these are likely to reduce yield but are only one factor among many variables affecting quality such as wine color.