VTechWorks Repository :: Browsing by Author "Zoecklein, Bruce W."

Browsing by Author "Zoecklein, Bruce W."

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Characterization of Cold Soak on Vitis vinifera L. cv. Cabernet Sauvignon Grape and Wine Volatiles Using an Electronic Nose System
Gardner, Denise M. (Virginia Tech, 2009-04-30)
The use of the electronic nose in the wine industry is an emerging technology. Although electronic nose systems have been used in other industries as tools to monitor fruit maturity or quality control, the use of these systems for wine analysis has been debated. Many electronic nose sensor types exist, but have often been accused of primarily discriminating varying ethanol concentrations of wines as opposed to aroma and flavor volatiles. This study evaluated the use of a commercial conducting polymer electronic nose to evaluate wines while minimizing ethanol interference. The first study presented evaluated the discrimination ability of an electronic nose with use of an ethanol baseline prior to wine evaluation. This experiment also determined the optimal wine temperature for electronic nose analysis. A second study reviewed the ability of the electronic nose to discriminate Cabernet Sauvignon grape and wine volatiles based on a pre-fermentation cold soak treatment. The electronic nose was used to monitor volatile changes throughout a five day cold soak, and to discriminate differences in control versus cold soak wines. These results were compared with juice and wine analytical data, GC-MS evaluation of individual volatiles, and sensory analysis of the finished wines. It was found that discrimination of wines improved from 33% to 60% when using an ethanol baseline. Influence of the baseline was indicated by a drop in sensor response prior to wine evaluation. A 30°C sample temperature was chosen for wine analysis based on sensor response and adequate discrimination in canonical distributions. The electronic nose was found to discriminate grape volatiles in cold soak musts as shown in canonical distributions at a 95% significance level. PCA distributions of electronic nose data, chemistry data, and GC-MS data showed varying degrees of discrimination based on analysis. Electronic nose data often showed 100% of variation of samples accounted by PC1. Despite differences in treatment by ENose and analytical data, sensory results did not find a difference in control and cold soak wines.
Commercial grape varieties for Virginia
Wolf, Tony Kenneth, 1956-; Dami, Imed E.; Zoecklein, Bruce W.; Warren, M. Kay (Virginia Cooperative Extension, 1999)
Commercial Grape Varieties for Virginia
Wolf, Tony Kenneth, 1956-; Dami, Imed E.; Zoecklein, Bruce W.; Warren, M. Kay (Virginia Cooperative Extension, 2005-09-01)
This publication makes recommendations for grape varieties that have demonstrated commercial suitability under the diverse growing conditions in Virginia.
Comparison of analytical methods for prediction of prefermentation nutritional status of grape juice
Gump, B. H.; Zoecklein, Bruce W.; Fugelsang, K. C.; Whiton, R. S. (American Society for Enology and Viticulture, 2002)
Five methods for evaluating nitrogen status were compared using 70 Cabernet Sauvignon juice samples: nitrogen by o-phthaldialdehyde (NOPA), arginine NOPA, enzymatic ammonia, Formol, and high-performance liquid chromatography (HPLC). Parallel recovery studies using model solutions of various amino acids and ammonia, presented singly and in combination, were also conducted. The results from two fruit-processing methods were compared using immature and mature berries. NOPA measurements were significantly higher in mature, pressed whole berry-derived samples, compared with homogenized juice. Adjustment of formaldehyde pH prior to analysis was found to be critical to consistency of the Formol method. Average amino acid recoveries for the Formol titration ranged from 82 to 99%. Average recovery for proline was 16.9 +/- 0.4%. Ammonium nitrogen was also recovered (84 +/- 3%) in the Formol procedure. Formol results trended significantly with NOPA. The correlation coefficient between Formol and NOPA plus NH4+ was 0.87, with Formol values being higher. The average deviation between the Formol and HPLC plus NH4+ and between the NOPA plus NH4+ and HPLC plus NH4+ was 7.3%.
Determination of ethyl carbamate in wine by solid-phase microextraction and gas chromatography/mass spectrometry
Whiton, R. S.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2002)
A method for the rapid determination of ethyl carbamate in wine by headspace solid-phase microextraction with detection by gas chromatography/mass spectrometry has been developed. The analysis parameters of fiber coating, extraction time, and sample temperature have been optimized. The optimized method of headspace sampling with a Carbowax/divinylbenzene fiber for 30 minutes has been found to be reproducible and linear from 10 to 80 mug/L, with a limit of detection of 9.6 mug/L. The method is simple, requires little operator effort, and can be automated.
Discriminating the Effects of Vineyard Management Practices on Grape and Wine Volatiles from Cabernet Franc and Merlot Grape Varieties Using Electronic Nose Systems
Devarajan, Yamuna Swetha (Virginia Tech, 2009-09-07)
Vineyard management practices are known to affect fruit composition and resultant wines, in part, by altering fruit volatiles. Methods currently used to evaluate the impact of vineyard practices on grape/wine composition include measuring physico-chemistry indices and performing wine sensory analyses. These activities are both time-consuming and destructive. Two electronic nose (ENose) systems: a hand-held conducting polymer-based and a portable surface acoustic wave-based systems were investigated as grape monitoring tools. Vineyard treatments included the effect of canopy side (East vs. West and North vs. South), cluster thinning (unthinned, 1 cluster/shoot, and 1 & 2 cluster/shoot) and ethanol spray (5% v/v) on Cabernet franc, Merlot and both varieties respectively. ENose data were obtained in the field (over two growing seasons for canopy side and in 2008 for cluster thinning and ethanol spray) and laboratory (2007 for canopy side), across different sampling dates and compared with nine-grape/eight-wine chemistry assays, GC/MS (cluster thinning) and wine aroma sensory evaluations (triangular difference testing). ENose results demonstrated 100% significant differences between all Cabernet franc and Merlot treatments. Grape/wine chemistry indices, for both Cabernet franc and Merlot, did not differ among treatments (except ethanol treatment) across sampling dates or growing seasons and vineyard management practices. Wine aroma sensory evaluations demonstrated only limited differences (3 out of 8 comparisons: East vs. West, 1 cluster/shoot vs. 1 & 2 clusters/shoot and 1 cluster/shoot and 1 & 2 clusters/shoot). The high level of discrimination by ENose systems may provide opportunities to enhance the understanding of vineyard management activities.
Discriminating the Effects of Vineyard Management Practices on Grape and Wine Volatiles from Cabernet Franc and Merlot Grape Varieties Using Electronic Nose Systems
Devarajan, Yamuna Swetha (Virginia Tech, 2009-08-07)
Vineyard management practices are known to affect fruit composition and resultant wines, in part, by altering fruit volatiles. Methods currently used to evaluate the impact of vineyard practices on grape/wine composition include measuring physico-chemistry indices and performing wine sensory analyses. These activities are both time-consuming and destructive. Two electronic nose (ENose) systems: a hand-held conducting polymer-based and a portable surface acoustic wave-based systems were investigated as grape monitoring tools. Vineyard treatments included the effect of canopy side (East vs. West and North vs. South), cluster thinning (unthinned, 1 cluster/shoot, and 1 & 2 cluster/shoot) and ethanol spray (5% v/v) on Cabernet franc, Merlot and both varieties respectively. ENose data were obtained in the field (over two growing seasons for canopy side and in 2008 for cluster thinning and ethanol spray) and laboratory (2007 for canopy side), across different sampling dates and compared with nine-grape/eight-wine chemistry assays, GC/MS (cluster thinning) and wine aroma sensory evaluations (triangular difference testing). ENose results demonstrated 100% significant differences between all Cabernet franc and Merlot treatments. Grape/wine chemistry indices, for both Cabernet franc and Merlot, did not differ among treatments (except ethanol treatment) across sampling dates or growing seasons and vineyard management practices. Wine aroma sensory evaluations demonstrated only limited differences (3 out of 8 comparisons: East vs. West, 1 cluster/shoot vs. 1 & 2 clusters/shoot and 1 cluster/shoot and 1 & 2 clusters/shoot). The high level of discrimination by ENose systems may provide opportunities to enhance the understanding of vineyard management activities.
Effect of canopy manipulation and fermentation on grape aroma components
Zoecklein, Bruce W. (Virginia Tech, 1995)
Several experiments were conducted to determine optimum methods for extraction, isolation and analysis of selected aroma components and the influence of grapevine canopy manipulation and fermentation on those components. A polymeric styrene resin (XAD-2) was evaluated for its ability to absorb and desorb five monoterpene alcohols, three monoterpene hydrocarbons, four monterpene oxides, two aromatic alcohols and a glucopyranoside from White Riesling juice at two different pH values. The percent recovery and the coefficients of variation for each compound was compared with a continuous Freon 11 extraction system. The percent recovery averaged 90% or greater for both systems with the coefficient of variation being smaller with the resin extraction. In two separate studies canopy manipulation was evaluated for the effect on aroma components using the XAD-2 resin isolation procedure. The influence of shoot topping to 10 or 20 nodes or ethephon application on grape aroma components was measured for three seasons. Canopy modification by both topping levels and ethephon treatment increased sunlight penetration into the canopy fruiting zone. Free volatile terpenes (FVT) were increased by ethephon in two of three seasons while shoot topping increased FVT and potentially free volatile terpenes (PVT) in one of three seasons. In the second separate three-year study, two to four leaves were removed from the fruiting zone of grapes grown on two training systems. Selective leaf removal increased sunlight penetration into the grape canopy but generally did not influence FVT. However, PVT was frequently higher in the leaf-pulled fruit including four of six commercial harvest dates. The total quantity of the bound geraniol, nerol, linalool, and a terpineol was higher in fruit from the leaf-pulled vines at harvest. Four strains of Saccharomyces cerevisiae were evaluated for their influences on free and conjugated aroma components of White Riesling grapes, immediately following and 45 days post-fermentation with lees or Sur lie. Fermentation generally reduced free terpenes except for «- terpineol, hotrienol, citronellol, and linalool oxides. Fermentation also increased free benzyl and 2-phenylethanol. In newly fermented and aged wines the concentrations of free volatiles were always below the sensory threshold for each compound. The potentially volatile terpenes (PVT) were Similar among treatments following fermentation, the exception being the Fermiblanc (FB) yeast strain. Additional hydrolysis of bound compounds occurred in each wine following lees storage, the exception being the wine fermented with the Fermiblanc (FB) strain.
Effect of canopy manipulation on rot incidence and rot metabolites of White Riesling (Vitis vinifera L.) grapes
Zoecklein, Bruce W. (Virginia Tech, 1993)
Several experiments were conducted to determine the influence of modifying the grapevine microclimate on the incidence of fruit rot and selected rot metabolites of Virginia grown White Riesling (Vitis vinifera L.) grapes. Due to the relatively high incidence of rot observed in these studies, an evaluation of the effects of rot on the sensory evaluation of juice and on selected aroma components was also undertaken. The effect of shoot topping to 10 or 20 nodes or the application of ethephon on the incidence of grape rot was measured for three seasons. Canopy modification by both topping and ethephon treatment increased sunlight penetration into the fruiting zone. Fruit rot incidence and the concentrations of rot-associated metabolites were significantly and mutually correlated. Fruit rots and rot metabolites were greatest with control and ethephon-treated vines and were least with vines whose shoots were topped to 10 nodes. In a separate three-year study, two to four leaves were removed from the fruiting zone of grapes grown on two training systems. Selective leaf removal generally increased sunlight penetration into the grapevine canopy. The incidence of Botrytis and sour rot as well as the concentrations of rot organism metabolites in harvested fruit were reduced by leaf removal. The effect of grape sour rot on general fruit chemistry, free volatile terpenes, potentially free volatile terpenes, selected polyols and rot metabolites was undertaken. Grape sour rot increased °Brix, glucose to fructose ratio, titratable acidity, tartaric acid, glycerol and gluconic acid. Grape sour rot reduced the concentrations of geraniol, nerol and linalool, while increasing oxidation products, aromatic alcohols and long chained alcohols. Grape juice sensory analysis appeared to be influenced by the severe fruit rot which occurred in both the control and to a lesser extent in canopy manipulated vines in both studies. The importance of fruit rot was demonstrated by both the production of odors, metabolites, and the destruction of native grape aroma constituents. Reductions in the incidence of fruit rot by selective leaf removal and shoot topping were demonstrated and were probably due to several microclimate factors that collectively increased evaporative potential and spray penetration into the fruit zone. The results illustrate that remedial canopy management practices that improve fruit zone porosity can mitigate the severe disease pressure that exists when rot-prone cultivars are grown in humid grape growing regions. The inability to reduce fruit rots further than noted in these studies may be due to the complex nature of fruit rots observed here, compared to those (principally Botrytis rot) examined in the majority of other canopy management studies.
The Effect of Complete Vineyard Floor Ground Covers and Root Pruning on Cabernet Sauvignon
Giese, William Gill Jr. (Virginia Tech, 2014-06-18)
Complete vineyard floor cover cropping and root pruning (RP) were evaluated for their ability to regulate excessive vegetative growth and improve berry and wine composition of ‘Cabernet Sauvignon’ (Vitis vinifera L.). Treatments were: tall fescue (Festuca arundinacea Shreb.) ‘KY-31’ and ‘Elite II’, hard fescue (Festuca ovina L.) ‘Aurora Gold’, perennial ryegrass (Lolium perenne L.), orchardgrass (Dactylis glomerata L.), and an under-trellis herbicide strip combined with KY-31fescue interrows. Compared to herbicide strip/non-root pruned (NRP), Elite II fescue reduced vine pruning weight (kg/vine) 28%, individual cane weight (g) 20%, and canopy leaf layer number 25%. KY-31 fescue/RP lowered vine pruning weights 29% compared to an 8% reduction in pruning weights of vines grown in herbicide strip/NRP plots from 2005 to 2010. KY-31 fescue produced the greatest biomass and stand density. With the exception of a yield reduction in vines grown with KY-31 fescue in 2006, cover crops minimally decreased grape yield. Yearly climatic variation had a greater effect on berry weight and composition (pH, TSS, TA) than did treatments. Limited treatment differences detected in chemical compounds by gas chromatography–mass spectrometry (GC-MS) analysis in wines made from treatment vines in 2010 were correlated to descriptive sensory terms. Cover crop water use, as evapotranspiration, determined by mini-lysimeter (ML), ranged from 3.28 mm/d for KY-31 fescue to 1.52 mm/d for herbicide-treated plots. In 2008, root biomass of vines grown on KY-31 fescue/RP was increased at the 60 to 80 and 80 to 100 cm soil depths compared to root biomass of KY-31 fescue/NRP vines at those depths. Cover crops minimally impacted vine water potential (ΨPD, Ψmd, Ψstem) and grapevine nitrogen levels relative to the herbicide strip, indicating that the grasses were not overly competitive with grapevines. Root pruning and complete vineyard floor cover crops favorably reduced grapevine vegetative growth, although treatment effects diminished over time, possibly in response to redistribution of grapevines’ roots and climatic variation at the site.
Effect of fermentation, postfermentation, and postbottling heat treatment on Cabernet Sauvignon glycoconjugates
Mansfield, A. K.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2003)
In Cabernet Sauvignon must, total and phenol-free glycosides (expressed as glycosyl-glucose) rose during fermentation while skin concentrations dropped. Wines were heated postfermentation, prior to dejuicing (rising 2 to 3degreesC per day from 23 to 42degreesC, and held for one day at 42degreesC), or after bottling (at 42degreesC for 21 days) to determine the effect on total glycosides, glycosidic fractions, and anthocyanin complexing. Pre-dejuicing thermal vinification resulted in higher total (12%) and phenol-free (18%) glycosides. Large polymeric pigments rose 208% and small polymeric pigments rose 41%. Skins had lower total glycosides (-16%), and no significant difference in phenol-free glycosides. Postbottling heat treatment resulted in lower total (-15%) and phenol-free (-16%) glycosides, and increased hue (25%). Large polymeric pigments increased 62% compared to control wines.
Effect of Foliar Nitrogen and Sulfur Applications on Aroma Profile of Vitis vinifera L. cv. Petit Manseng using Modified Quantitative Descriptive Analysis, SPME GC-MS and Electronic Nose Technology
Kelly, Molly Kathleen (Virginia Tech, 2013-06-12)
Petit Manseng grapes harvested in 2011 and 2012 were fertilized with soil nitrogen at 0, and 30 kgN/ha, foliar nitrogen at 15kg/ha and foliar nitrogen plus sulfur at 15kg/ha and 5kg respectively. Point quadrat analysis demonstrated foliar nitrogen alone and nitrogen plus sulfur treatments increased percent gaps and lower leaf layer numbers. Berry juice samples differed in ammonia, arginine and yeast assimilable nitrogen concentration. Total glycosides were 25 percent higher in the foliar nitrogen treatment versus the control treatment. Electronic nose measurements on field clusters and laboratory berry analyses was different among treatments in volatile content. Harvest samples underwent acid or enzyme hydrolysis of precursor fractions. Solid phase microextraction (SPME) and gas chromatography-mass spectrometry (GC/MS) analysis identified 27 free aroma and flavor compounds and 52 bound compounds. Lactones and carboxylic acids were the major components of the free fractions while bound fractions had increased concentrations of alcohols, esters and terpenes compared to the free fraction. With nitrogen fertilization, acid and enzyme hydrolysis had reduced concentrations of some higher alcohols and carboxylic acids. Acid hydrolysis released more terpenes with nitrogen treatments versus enzymatic hydrolysis. Ester content was increased in both acid and enzyme hydrolysis fractions in vines receiving nitrogen treatments. For descriptive analysis, eight trained panelists described aroma, flavor, texture/mouthfeel and aftertaste attributes. Analysis of Variance (ANOVA) demonstrated that wines were a significant source of variation with 23 of the 24 attributes used. Wine principal component analysis (PCA) of aroma attributes explained 23.5% of the variation from PC1, while flavor-by-mouth and texture/mouthfeel attributes explained 26.3% of the variation due to PC1. The aim of this study was to develop descriptive terms for Petit Manseng and determine the influence of fruit nitrogen levels on the aroma and flavor profile of this cultivar.
Effect of Training Systems on Viognier (Vitis vinifera L.) Grape and Wine Glycosides and Volatile Compounds
Millard, Lindsay Theresa (Virginia Tech, 2005-03-02)
Viognier (Vitis vinifera L.) grapes were grown in Northern Virginia for three seasons using three different training systems in a randomized complete block design consisting of Vertical Shoot Positioned (VSP), Smart Dyson (SD), and Geneva Double Curtain (GDC), and evaluated for the effects on grape and wine glycosides and volatile compounds. Fruit was harvested at the same Brix each season, and differences in berry weights were not observed. VSP-trained vines had the lowest crop load and lowest light levels in the fruit zone. Seventeen volatile compounds were analyzed using headspace solid-phase microextraction, GC-MS. Fruit showed differences in linalool, Ã¡-terpineol, Ã¢-damascenone, and n-hexanol concentrations among the training systems. Wines showed differences in both grape-derived and fermentation-derived volatiles. SD had the highest concentration for most of the free volatiles quantified in both the juice and wine. VSP had lower phenol-free wine glycosides all three seasons and lower phenol-free juice glycosides one season. Triangle difference sensory testing demonstrated differences between GDC and SD in wine aroma and flavor, and differences between VSP and SD in flavor, for two of three seasons.
Effect of vertical shoot-positioned, smart-dyson, and Geneva double-curtain training systems on Viognier grape and wine composition
Zoecklein, Bruce W.; Wolf, T. K.; Pelanne, L.; Miller, M. K.; Birkenmaier, S. S. (American Society for Enology and Viticulture, 2008-03)
Viognier grapes grown in northern Virginia and resultant wines were evaluated as a function of training system. Treatments included vertical shoot-positioned (VSP), Smart-Dyson (SD), and Geneva double curtain (GDC), with vines of all treatments spaced 2.4 m apart in 3.0 m wide rows. In addition to increased cluster numbers and crop yield, GDC training generally increased fruit zone sunlight interception and fruit exposure, while it decreased cane pruning weights per meter of cordon, compared with SD and VSP. Crop adjustments were made between bloom and veraison in six seasons, to result in average yields of 10.5 kg/vine (GDC), 9.9 kg/vine (SD), and 6.0 kg/vine (VSP), with the lower SD canopy bearing 30 to 40% less crop than the corresponding upper SD canopy. Crop loads (yield/cane pruning weight) were generally between 4 and 12; GDC crop load approached 20 in three seasons, while SD approached 14 in one. Leaf area per crop ratio was determined one season and exceeded 1.8 m(2)/kg of fruit for all systems. Fruit was harvested at similar Brix values, with differences in berry weight, pH, titratable acidity, and malic and tartaric acids among treatments generally not significant. Volatile compounds were analyzed using headspace solid-phase microextraction GC-MS. Fruit showed consistent differences in linalool, alpha-terpineol, beta-damascenone, and n-hexanol concentrations among training systems. SD had the highest concentration of most free volatiles quantified in both juice and wines, while GDC wines frequently had the highest concentration of phenol-free glycosides. Triangle difference sensory testing demonstrated differences between GDC and SD in wine aroma and flavor and between VSP and SD in flavor. GDC wines generally had higher fruity and floral aromas compared with the other systems.
Effect of vineyard management of Cabernet Sauvignon (Vitis vinifera L.) grape glycosides
Yoder, Carleton C. (Virginia Tech, 1996)
Quantification of grape glycosides has been suggested as an objective index of grape quality. Two studies were undertaken to observe the influence of vineyard management on grape glycosides. In the first study, three crop levels from mature Cabernet Sauvignon (Vitis vinifera L.) vines grown in eastern Virginia were evaluated for their influence on grape glycosides, expressed as red-free glycosyl glucose (GG). Crop levels averaged 3.2, 5.1, and 6.4 kg/vine resulting in leaf area to fruit weight ratios (cm²/g) of 34.4, 27.0 and 19.2, respectively. Red-free GG was greatest in juice from fruit of the low treatment at four of seven sampling dates, including harvest. Phenolic glycosides were found to comprise as much as half of the total GG value. In a second study, shoot thinning, mechanical and hand fruit zone leaf removal of mature Cabernet Sauvignon grapevines were evaluated for their influence on red-free GG. Two shoot densities were examined, each with no leaf removal (No LR), mechanical leaf removal (M LR) or mechanical plus hand leaf removal (M+H LR) imposed five weeks post-bloom. Red-free GG was increased by leaf removal of shoot thinned vines and was greatest with mechanical plus hand leaf removal.
The Effect of Wine Matrix Ingredients on 3-Alkyl-2-methoxypyrazines Measurements by Headspace Solid-Phase Microextraction (HS-SPME)
Hartmann, Peter J. (Virginia Tech, 2002-12-02)
The effect of wine matrix ingredients and conditions on the headspace (HS) sampling of 3-alkyl-2-methoxypyrazines was investigated with solid-phase microextraction (SPME) and capillary gas chromatography, using a nitrogen phosphorus detector. Changes in the recovery of 3-ethyl-, isopropyl-, sec-butyl-, and isobutyl-2-methoxypyrazines from the static headspace of synthetic wine matrices spiked with 5mg/L of each analyte were investigated and reported as a function of SPME fiber type, extraction time, and temperature. The influence of pH, ethanol, phenolics, and ground oak was studied. DVB/Carboxen?/PDMS SPME fibers at an extraction temperature of 50°C for 30 minutes with 30% (w/v) added sodium chloride resulted in the highest analyte recoveries. Although, PDMS (100 micron) SPME fibers at an extraction temperature of 35°C for 30 minutes with 30% (w/v) added sodium chloride resulted in the lower analyte recoveries, the fiber remained functional after 50 to 75 analyses after other coatings deteriorated. Changing the sample ethanol concentration from 0 to 20% (v/v) resulted in an exponential decrease in the recovered analytes. Below pH 2, there was extensive loss of the analytes in the headspace. No measurable impact on alkylmethoxypyrazine headspace concentrations was observed with exposures to selected phenolics and to ground oak.
Effects of Capture and Return on Chardonnay (Vitis vinifera L.) Fermentation Volatiles
Hodson, Emily (Virginia Tech, 2004-09-15)
Effectiveness of a capture and return system for the partial retention of fermentation volatiles, as a means of improving white wine quality, was evaluated. Twenty-three aroma-active volatiles including ethyl esters, acetate esters, fusel alcohols, and fatty acids, were quantified using head-space solid phase microextraction with GC/MS. Volatile analysis of fermentations maintained at 15ºC demonstrated a trend of increased concentrations of ethanol, esters and ethyl esters of fatty acids and decreased concentrations of fusel alcohol acetates, fatty acids and higher alcohols in treatment wines. When fermentation temperature was maintained at 15ºC there was increased concentration and retention of fusel alcohols, fatty acids and higher alcohols compared to 15ºC. Sensory analysis of wines fermented at 15°C, using triangle difference testing, indicated variable differences in aroma among treatments.
The effects of different processing parameters (cold soak and percent alcohol (v/v) at dejuicing) on the concentrations of grape glycosides and glycoside fractions and glycosidase activities in selected yeast and lactic acid bacteria
McMahon, Heather (Virginia Tech, 1998-12-03)
Grape-derived aroma and flavor precursors exist partially as non-volatile, sugar-bound glycosides. Hydrolysis of these compounds may modify sensory attributes and potentially enhance wine quality. Cold soak (prefermentation skin contact) at two temperatures and alcohol content (%, v/v) at dejuicing were monitored to determine effects on Cabernet Sauvignon glycoside concentration. Total, phenolic-free, and red-free glycoside concentrations were estimated by the quantification of glycosyl-glucose. Cold soak (5 days at 10° C) increased total glycosides by 77%, red-free glycosides by 80%, and phenolic-free glycosides by 96%. Ambient soak (3 days at 20° C) enhanced color extraction, and increased total glycosides by 177%, red-free glycosides by 144%, and phenolic-free glycosides by 106%. Wines produced by early pressing (10% sugar) had 25% more total and red-free glycosides than late press (0.25% sugar). After post-fermentation malolactic fermentation, total glycosides were 14% lower and phenolic-free glycosides were 35% lower. In a second study, the activities of a-L-arabinofuranosidase, b-glucosidase, and a-L-rhamnoyranosidase were determined in model systems for thirty-two strains of yeasts belonging to the following genera: Aureobasidium, Candida, Cryptococcus, Hanseniaspora, Hansenula, Kloeckera, Metschnikowia, Pichia, Saccharomyces, Torulaspora, and Brettanomyces (10 strains); and seven bacteria (Leuconostoc oenos strains). Only one Saccharomyces strain exhibited -glucosidase activity, but several non-Saccharomyces yeast species had substantial production. Aureobasidium pullulans hydrolyzed a-L-arabinofuranoside, b-glucoside, and a-L-rhamnoyranoside. Eight Brettanomyces strains had -glucosidase activity. Location of enzyme activity was determined for those species with enzymatic activity. The majority of -glucosidase was located in the whole cell fraction (66%), followed by the permeabilized fraction (35%), and extracellular production (2%). Aureobasidium pullulans was also capable of hydrolyzing grape glycosides.
The effects of post-fermentation and post-bottling heat treatment on Cabernet Sauvignon (V. vinifera L.) glycosides and quantification of glycosidase activities in selected strains of Brettanomyces bruxellensis and Oenococcus oeni
Mansfield, Anna Katharine (Virginia Tech, 2001-06-19)
Thermal processing has been used as a means of modifying the sensory aspects of wine. Cabernet Sauvignon wines were heated prior to dejuicing (3C per day from 25C to 42C) or after bottling (42C for 21 days) to determine the effects on total glycosides and glycosidic fractions. Total and phenol-free glycosidic concentrations in the wine and skins were quantified by analysis of glycosyl-glucose. Pre-dejuicing thermal vinification resulted in higher total glycosides (12%), phenol-free glycosides (18%), total hydroxycinnamates (16%), large polymeric pigments (LPP) (208%) small polymeric pigments (SPP) (41%), and lower monomeric pigments (42%) in wines. Skins had lower total glycosides (-16%), and no significant difference in phenol-free glycosides. Post-bottling heat treatment resulted in lower total (-15%) and phenol-free (-16%) glycosides, increased hue (25%), a 62% increase in LPP and a 29% decrease in monmeric pigments. A second study investigated the potential of enological spoilage microorganisms to affect wine aroma, flavor, and color. The activities of b-glucosidase were determined in model systems for fourteen strains of Brettanomyces bruxellensis yeast and nine strains of lactic acid bacteria (Oenococcus oeni). All Brettanomyces strains and seven Oenococcus strains exhibited enzymatic activity. B. bruxellensis b-glucosidase activity was primarily intracellular; O. oeni showed some extracellular activity. Yeasts and bacteria showing activity greater than 1000 nmole mL-1 g -1 for Brettanomyces, or 100 nmole mL-1 g -1 for Oenococcus, were evaluated for their effect on Viognier grape glycosides. Neither was active on native grape glycosides.
Effects of prohexadione-calcium on grape yield components and fruit and wine composition
Lo Giudice, Danielle; Wolf, Tony K.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2004)
Prohexadione-calcium (prohexadione-Ca) was applied to field-grown Cabernet franc, Cabernet Sauvignon, Chardonnay, and Seyval to evaluate rates and timing effects on fruit yield components and on fruit and wine composition. Berries per cluster, berry weight, cluster weight, and clusters per shoot in the subsequent season were all decreased by multiple, prebloom plus postbloom, applications to Cabernet Sauvignon and Cabernet franc. Similar reductions in current season components of yield were observed with Seyval. Application (250 mg/L) to single clusters of Cabernet Sauvignon and Chardonnay at bloom, or in the one-to-two-week prebloom period decreased fruit set, whereas applications one to two weeks postbloom reduced berry weight, with no impact on fruit set. Berry weight reduction correlated to increased color intensity (420 nm + 520 nm), total anthocyanins, total phenols, and phenol-free glycosyl-glucose (PFGG) in Cabernet Sauvignon. In a separate experiment, prohexadione-Ca increased Cabernet franc must color intensity, total anthocyanins, and total phenols, despite having, minimal effects on berry weight or crop yield. Aroma and flavor triangle difference tests did not distinguish treatment differences with young Cabernet franc wines. This study of prohexadione-Ca effects on grape reproductive development illustrated that berry set and berry weight were responsive to application timing, with the one-to-two-week period after bloom most sensitive to reductions in berry weight. The concurrent effects on fruit composition were generally positive, while the full impact on wine quality remains equivocal, but worthy of further evaluation.